It has been known that an objective lens system of an apochromatic telescope has a combination of a single positive lens element and a single negative lens element, which are made from lens materials having different dispersion powers. Since the objective lens system of an astronomical telescope has a long focal length, correction of axial chromatic aberration is especially important; in recent years there have been many examples of fluorite or special low-dispersion glass being used to reduce the secondary spectrum of the axial chromatic aberrations.

A telescope focuser allows you to explore the skies and see well beyond the capacity of the human eye. The telescope has certainly come a long way from when Galileo first viewed the craters of the moon in 1609. Now, its possible for anyone to buy a telescope, limited only by their budget. However, there are some things to consider when making such a purchase. Read this eHow to learn more.Buy your telescope from a telescope store or online store. A department store telescope will not have the same quality as one sold by a store that focuses on the instrument.

Join an astronomy club and look through the telescopes that the other members or the club provide. Ask a lot of questions, and learn which intane telescopes perform the best, and which ones the other members prefer. You may find such clubs listed at your local planetarium or museum, or even a department store.Decide the size of the telescope you wish to buy. Generally speaking, smaller telescopes are smaller and are easier to carry as well as less expensive. However, the smaller telescopes do not always come with added features like a computer in which you can punch in coordinates.

 

source:myblog intane

An achromatic Lens sight, commonly called a scope, is an optical device used to give additional accuracy using a point of aim for firearms, airguns and crossbows. Other sighting systems are iron sights, reflex sights, and laser sights.The first experiments directed to give shooters optical aiming aids go back to the early 17th century. For centuries different optical aiming aids and primitive predecessors of telescopic sights were created that had practical or performance limitations. The first Apochromatic refractor telescope based telescopic sight was built in 1880 by August Fiedler (Stronsdorf, Austria), forestry commissioner of Prince Reuss. Telescopic sights with extra long eye relief are available for handgun and scout rifle use. A historic example of a telescopic sight with a long eye relief is the German ZF41 which was used during World War II on Karabiner 98k rifles.

Telescopic sights are classified in terms of the optical magnification and the objective lens diameter, e.g. 10×50. This would denote 10 times magnification with a 50 mm objective lens. In general terms, larger objective lens diameters, due to their ability to gather larger amounts of light, provide a larger exit pupil and hence provide a brighter image at the eyepiece. On fixed magnification sights the magnification power and objective diameter should be chosen on the basis of the intended use.

There are also apochromatic telescope sights with variable magnification. The magnification can be varied by manually operating a zoom mechanism. Variable sights offer more flexibility regarding shooting at varying ranges, targets and light conditions and offer a relative wide field of view at lower magnification settings. The syntax for variable sights is the following: minimal magnification – maximum magnification × objective lens, for example, 3–9×40.

Confusingly, some older telescopic sights, mainly of German or other European manufacture, have a different classification where the second part of the designation refers to 'light gathering power.' In these cases, a 4×81 (4× magnification) sight would be presumed to have a brighter sight picture than a 2.5×70 (2.5× magnification), but the objective lens diameter would not bear any direct relation to picture brightness, as brightness is affected also by the magnification factor. Typically objective Achromatic lenses on early sights are smaller than modern sights, in these examples the 4×81 would have an objective approximately 32mm diameter and the 2.5×70 might be approximately 25mm.

source:funrctoys.blogalbums

FIG. 1 is a schematic view of a covered water dispensing probe and mechanism for uncovering the probe on insertion of an inverted filling machines into the dispenser;
FIG. 2 is a second embodiment of a covered water dispensing probe and uncovering mechanism;
FIG. 3 is an uncovered but sealed water dispensing probe;
FIG. 4 is an open water dispensing probe; and
FIG. 5 is a schematic illustration of a closed water bottle and closed water dispensing probe which are automatically opened when joined.

Referring to FIG. 1, the neck of an inverted water bottle 10 is shown being lowered into a bottle guide 11 which is located in the top of the water dispenser. The water bottle usually contains approximately five gallons of water and is made of plastic or glass. An elongated plastic cap 13 covers the open mouth of the water bottle and also has a ridge or bead 15 along the side of the cap which forms a seal with the interior of bottle guide 11. Cap 13 is conventional on water bottles and is usually torn off before the water bottle is inverted and placed into the water dispenser. The opening of the water bottle, however, exposes the fresh water inside the bottle to ambient contaminants, even if only for a short time. It is preferred to leave the bottle closed at all times and to open the bottle in the water dispenser. U.S. Pat. No. 4,699,188 discloses a cap for a bottled water equipment which has an inwardly turned, recessed portion, extending backwardly into the neck of the bottle, which is closed by a displaceable cap. The device disclosed in this application will function with the aforementioned cap and will also function with a conventional plastic cap.

When the water bottle is inserted, the cap of the water bottle strikes the actuating rod 47 pushing camming surface 59 downwardly against cam surface 61 on cap 63 causing the cover to open. The continued downward motion of the water bottle forces platform 53 and supported tube 69 downwardly until the bottle comes to rest against annular stop 45. Before the bottle reaches stop 45, the sharpened end 19 of probe 17 will cut a flap 81 in cap 13 on the water bottle. In FIG. 1, flap 81 is shown cut before the water bottle reaches probe 17, for clarity. The bottle would normally be closed until probe 17 pierces the cap cutting flap 81. Since probe 19 is sharpened, the edge of the probe is relieved or angled inwardly which causes the probe to cut a hole in cap 13 slightly smaller than the outer diameter of probe 17. This smaller hole in the cap tightly grips the outer surface of probe 17 precluding any air or water leakage.

With the filling machines in place, dispensing valve 29 can be actuated to draw water from the bottle. The water will push open check valve 35 and flow outwardly through spigot 33. Any air needed to relieve the partial vacuum in the bottom of water bottle 10 will flow inwardly through tube 41 and check valve 43 and bubble upwardly through the water to the inverted bottom of the bottle. It can be seen that the system is completely sealed with the exception of the filtered air source. The filter used with the air source can be a single or compound filter designed to protect the water from the specific contaminants in the air surrounding the water dispenser. If biological materials are present, a microfilter can be used. If organic solvents are present, an activated charcoal filter can be used and if dust is present, a coarse paper or filberglass filter can be used. For mixed contaminants, the filter can be assembled with layers of different filter materials to protect the water.

As the water bottle enters bottle guide 11, it forces actuating rod 97 downwardly which, as previously described, causes cover 113 to open. The water bottle continues downwardly until probe 91 displaces the cap from the interior of the water bottle and the bottle comes to rest on the shoulders of bottle guide 11. A guide rod 123 is provided for controlling the motion of tubular member 103 as it is pushed downwardly. A coil spring 125 is positioned about probe 91 and urges the cover assembly upwardly. A flange 127 is attached to the side of tubular member 103 and has an aperture 129 therein for guiding flange 127 upon rod 123. A pin 131 projects through the end of rod 123 and prevents the cover assembly from being pushed beyond the end of probe 91.

Similar check valves and dispensing conduits can be attached to probe 91, as well as a filtered air source 41, to provide an enclosed and sealed water system. The cover of FIG. 2 is similar to the cover of FIG. 1 in that it protects the end of the probe from access to ambient contaminants when a filling machines is not in position.

In FIG. 3, a dispensing system is shown in which the end of the probe is not protected from ambient contaminants while the interior of the probe and the water conduit delivery system is sealed. A bottle guide 11 is again provided for centering an inverted water supply bottle 10 as it is inserted into the water dispenser. A plastic cap 13 closes the end or mouth of the water bottle. Cap 13 has a raised bead 15 for forming a seal against the interior of bottle guide 11. In this figure, as in FIG. 1, the cap of the water bottle is shown as cut while the bottle is separated from the probe. This has been done to facilitate the explanation of the invention. It is obvious that the cutting takes place after the cap is contacted and penetrated by the probe.

When a bottle using cap 181 of FIG. 5 is to be drained, a sealing member (not shown) can be pulled off the end of the collar exposing valve member 187. The bottle can then be inverted and lowered into bottle guide 11 which centers the neck of bottle 10 above tubular member 201. As the bottle descends, valve member 187 in cap 181 and valve member 217 in tubular member 201 are pushed backwardly, opening the fluid passage from the interior of water bottle 10 around the valve members and into tubular member 201 where the water can be distributed in the water dispensing system, as shown in FIGS. 4 and 1. Filtered air is again supplied from a source 41 into the side of tubular member 201. A flap check valve 43 is again used to close the source of filtered air. When water bottle 10 is emptied, it can be raised upwardly out of bottle guide 11 which causes valve member 187 in cap 191 to close the bottled water equipment , protecting the inside from contamination while valve member 217 closes the water dispensing system.

From the above description, it can be seen that a sealed water dispensing system is provided which no longer uses the conventional reservoir for containing water. The water is delivered directly from the water supply bottle to a water dispensing conduit or plumbing inside the water dispenser with the air needed to displace the partial vacuum in the bottom of the water supply bottle being supplied from a filtered source. By using the system of the present invention, the water is substantially protected from all airborne contaminants.

 

source:townhall|bottled water equipment

Whether you use at school, at work or a hobby, it is a microscope is an important investment. It is important to find an apochromatic telescope that offer outstanding performance, simple to operate and for many years. Everything is a waste of time and money. As such, you want to learn how to shop for a microscope.

 

 

 

 

 

1.Find for Apochromatic refractor metal or metal alloy. These microscopes are usually very strong and durable.

2.Select more neon lights. Fluorescent lighting is not as hot as an incandescent light. The heat of the bulbs can sometimes kill small organisms on a slide.

3.Pick an eyepiece with a wide range of size of at least 18 mm. The large opening in a wide field eyepiece causes less than one through a small opening eyestrain.

4.Opt a binocular eyepiece. These eyes can be your samples with both eyes (instead of a monocular eyepiece, which is only a hole for one eye view). With both eyes is a better approach minimizes eyestrain.

5th Select an achromatic lens . This type of lens is designed for color correction, so you can see all the colors of the spectrum by it. Achromatic objective is not allowed to see certain colors when they are through.

6.Choose Microscope German industry standard (DIN) of the lens. This is the most common form of the lens microscope that is easily lost from most microscope dealers or broken interchangeable.

7.Get focus of a microscope in order. Not all of microscope is this feature available. Fine tuning approach allows the details of a sample that would otherwise remain concealed.

8.Shop microscopy approach to Metal Gear. Gears of other materials that break easily and wears quickly.

 

source:intane|microscope

A diffractive-refractive achromatic lens according to the present invention includes: a refractive lens system that includes a positive lens made from crown-glass having relatively small dispersion; a negative lens made from flint-glass having relatively large dispersion; and a diffractive grating for correcting the longitudinal chromatic aberration of the refractive lens system.

Secondary spectrum of the longitudinal chromatic aberration cannot be corrected only by the refractive achromatic lens system made from the crown glass and the flint glass, while it is possible to choose a combination of glasses such that the refractive lens system exhibits longitudinal chromatic aberration that is substantially proportional to wavelength, i.e., the back focus of the refractive lens system decreases as the wavelength becomes shorter. For example, the combination is obtained by decreasing power or dispersion of a negative lens of a conventional achromatic doublet.

On the other hand, it is known that a value corresponding to Abbe number for a diffractive lens is equal to--3.453. The negative sign of the value reflects the opposite sense of the dispersion when compared with that of glasses, and its low magnitude is an indication of the large dispersion. That is, the positive diffractive lens has a longitudinal chromatic aberration such that back focus increases as wavelength becomes shorter. It is also known that the chromatic aberration of the diffractive grating is substantially proportional to wavelength.

Therefore, a use of a diffractive grating having small positive power in association with the refractive lens system having the chromatic aberration proportional to wavelength enables to reduce secondary spectrum of longitudinal chromatic aberration.Telescopes are divided into two basic categories: reflectors and refractors. Both gather and focus light to magnify images. The reflector apochromatic telescope is designed with a concave primary mirror at the bottom of the tube that reflects light onto a flat secondary mirror and brings the image into focus in the eyepiece. The refractor telescope uses a convex lens that refracts parallel rays of light into a single focal point, magnifying the image in that is viewed in the eyepiece.

There are nine embodiments described hereinafter. The refractive lens system includes a non- achromatic doublet in first, second and third embodiments. In fourth through ninth embodiments, the refractive lens system consists of a combination of a refractive achromatic lens and an additional lens. In any cases, the diffractive grating is preferably formed on one surface of the lenses to reduce both manufacturing cost and size.In 1608, Jassen, Lipershey and Metius invented the first refractor telescope. In 1611, the use of a convex lens as an eyepiece was invented by Johannes Kepler. In 1733, Chester Hall invented the achromatic lens by creating a lens made of two pieces of glass that were assembled together. The first reflector telescope appeared in the early 1600s. In 1668, Sir Isaac Newton designed the reflector telescope focuser with the use of two mirrors inside a hollow tube to gather and focus light into the eyepiece.

In the fourth through ninth embodiments, the refractive lens system includes a refractive achromatic lens and an additional refractive lens. The refractive achromatic lens is corrected in chromatic aberration at two different wavelengths, while secondary spectrum cannot be corrected. Thus, the back focus of the refractive achromatic lens increases as wavelength becomes shorter in a range shorter than F-line. On the other hand, the additional refractive lens is designed so that the refractive lens system, which is a combination of the refractive achromatic lens and the additional refractive lens, generates longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of the refractive lens system decreases as the wavelength becomes shorter. The proportional chromatic aberration of the refractive lens system can be corrected by the diffractive grating.

In these embodiments, since the refractive achromatic lens can be selected from conventional achromatic lenses , an attachment that includes the positive refractive lens and the diffractive grating is only required as an additional component. The refractor telescope is ideal for viewing distant celestial objects. Although the image is inverted when viewed through the eyepiece, this is of little consequence for celestial viewing. It is the preferred scope for deep sky viewing of remote objects like galaxies and star clusters. It is also a good scope to use for astrophotography.
The reflector telescope is ideal for viewing the moon or planets and other closer objects.

In the seventh, eighth and ninth embodiments, the additional lens and the diffractive grating is arranged at a convergent side of the refractive achromatic lens, and the additional refractive lens includes a lens having a convex surface directed to the refractive achromatic lens.

With this construction, since paraxial marginal rays from the refractive achromatic lens are strongly converged by the strong convex surface of the additional refractive lens, it generates chromatic aberration such that the back focus decreases as the wavelength becomes shorter. The other surface of the additional refractive lens does not generate large chromatic aberration, because incident height of the paraxial marginal rays converged by the strong positive surface at the other surface become small. Since the required longitudinal chromatic aberration for the additional refractive lens is generated by the strong convex surface, the additional refractive lens may have positive or negative refractive power.

Advantages of the apochromatic telescope are that it requires little care and is easy to use, has good image clarity with good color, has a sealed tube that prevents imaging degradation due to air currents and provides protection for the optics inside the tube, and the lens is aligned and mounted permanently.
Advantages of the reflector are that it is compact, portable and produces clear, bright images. The refractor telescope is more expensive than a reflector, is larger and bulkier than a reflector, suffers some color distortion and is limited to smaller apertures within a reasonable price range.
The reflector telescope requires adjustment to the optics to maintain the best quality, mirrors may require re-coating periodically to maintain quality, it is complicated to clean and maintain, and it's not suitable for viewing terrestrial objects.

Many erroneously believe that purchasing a telescope with a high magnification will provide a better image and allow them to view distant objects clearly. Because the amount of light gathered determines to a large part how well you will see an image, the size of the aperture is actually more important than the magnification of the lens. The aperture of a telescope is the size of the opening at the end of the tube that allows light to enter the scope.

A diffractive-refractive achromatic lens includes a refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of the refractive lens system decreases as the wavelength becomes shorter and a diffractive grating for correcting the longitudinal chromatic aberration of the refractive lens system. The refractive lens having such a chromatic aberration includes a positive lens having relatively small dispersion and a negative lens having relatively large dispersion. Further, the following condition (1) should be satisfied: 0.005<f/fD <0.2

Whether you're using it for school, work or a hobby, a microscope is a significant investment. It is important to find a microscope that will deliver exceptional performance, be easy to use and last for many years. Anything less is a waste of your time and money. As such, you'll want to learn just how to shop for a microscope.Look for microscopes made of metal or a metal alloy. These microscopes are usually quite sturdy and last the longest.Choose fluorescent lighting over incandescent. Fluorescent lighting is not nearly as hot as light from an incandescent bulb. The heat from incandescent lighting can sometimes kill small organisms on a slide.Pick an eyepiece with a wide field opening of at least 18 mm. The large opening in a large field eyepiece will cause less eyestrain than looking through a tiny opening.

a refractive lens system that comprises a refractive achromatic lenses that is corrected in chromatic aberration at two wavelengths and an additional refractive lens, said refractive achromatic lens being provided with a positive lens having relatively small dispersion and a negative lens having relatively large dispersion, said refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that a back focus of said refractive lens system decreases as the wavelength becomes shorter; and a positive diffractive grating that corrects said longitudinal chromatic aberration of said refractive lens system,wherein the following condition is satisfied: 0.005<f/fD <0.2The diffractive-refractive achromatic lens according to claim 3, wherein said additional lens is arranged at a convergent side of said refractive achromatic lens, and wherein said additional refractive lens comprises a lens having a convex surface directed to said refractive achromatic lens.

Opt for a binocular eyepiece. These eyepieces allow you to look at your specimens with both eyes (rather than a monocular eyepiece, which only has an opening for one eye). Using both eyes gives you better focus and minimizes eyestrain.Select an achromatic lens. This type of lens is designed for color correctness, meaning it will allow you to see all colors of the spectrum through it. A lens that is not achromatic may not let you see certain colors when you look through it.Choose a microscope with a Deutsche Industrie Norm (DIN) lens. This is the most common type of telescope focuser , making it easily replaceable by most microscope dealers if it should get lost or broken.

A diffractive-refractive achromatic lens that has a positive resultant power, said lens comprising:
a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths;an additional refractive lens that is arranged at a convergent side of said refractive achromatic lens, said additional refractive lens including a lens having a strong convex surface directed to said refractive achromatic lens to generate longitudinal chromatic aberration such that the back focus of the refractive lens system, which includes said refractive achromatic lens and said additional refractive lens, decreases as the wavelength becomes shorter; anda positive diffractive grating that is formed on one surface of said additional refractive lens to correct said longitudinal chromatic aberration of said refractive lens system,

Get a microscope with fine focus. Not every microscope comes with this feature. Fine focus allows you to hone in on details of a specimen that may otherwise remain unseen.Shop for a microscope with metal focus gears. Gears made from any other material will break easily and wear out quickly.A diffractive-refractive achromatic attachment that is attachable to a refractive achromatic lens being corrected in chromatic aberration at two different wave lengths, said attachment comprising:an additional refractive lens that generates longitudinal chromatic aberration such that the back focus of the refractive lens system, which includes said refractive achromatic lens and said additional refractive lens decreases as the wavelength becomes shorter; and a positive diffractive grating that corrects said longitudinal chromatic aberration of said refractive lens system.

The present invention relates to an achromatic lens to be used as a collimator lens, or an objective lens for a telescope. Particularly, the present invention relates to a diffractive-refractive achromatic lens that includes a refractive lens system provided with a diffractive grating.

Conventionally, an achromatic lens has been well known and used as a collimator lens or an objective lens. An example of the achromatic lens employs two thin lenses: one being a lens having large positive power that is made from crown glass having relatively low dispersion; and the other being a lens having small negative power that is made from flint glass having relatively high dispersion. The resultant power is therefore positive, while the dispersion is neutralized.

Since optical glass has dispersion such that refractive index thereof increases with decreasing wavelength of light, a positive refractive lens has longitudinal chromatic aberration where a back focus of the lens decreases as wavelength becomes shorter. The achromatic doublet corrects the chromatic aberration of the positive lens by using a negative lens that has opposite chromatic aberration. If the normal optical glasses are used for constituting the conventional type of the Apochromatic refractor , it is impossible to correct the secondary spectrum sufficiently. Because refractive index of glass increases as wavelength becomes shorter as described, while increasing degree of the flint glass is larger than that of the crown glass in short wavelength range. Then the chromatic aberration of the doublet is overcorrected (backfocus becomes too long) in the range shorter than F-line.

In order to suppress the secondary spectrum of the longitudinal chromatic aberration with the conventional type of the achromatic lens, fluorite or anomalous dispersion glass should be used. However, these materials are too expensive.

The invention relates to a telescope, comprising an eyepiece, an objective and an axially displaceable focusing optics arranged between the eyepiece and the objective.From U.S. Pat. No. 4,296,793, a telescope is known which relates to both monocular and binocular apochromatic telescopes . The telescope known from this document had the object of providing a telescope with a variable magnification with improved optical properties. This object was attained by providing an axially displaceable lens arranged behind the objective in the direction from the objective to the eyepiece, instead of changing the magnification by means of the eyepiece. The objective group L  11   is a focusing group and is thus also mounted for displacement in the axial direction.

Acquire a pair of lenses - a large convex lens and a small concave one. (Convex lenses are thicker in the center than at the edge; concave ones are thinner in the center.)Find two cardboard tubes that will allow one to slide inside the other.Figure out how far apart the lenses should be by looking through the smaller lens while holding the larger one out in front of you. When you can focus on an object in the distance, measure how far it is between the two lenses.

Either a motor or a manual drive can be provided for adjusting the magnification. The motor drives are respectively provided with a friction clutch in order to avoid overloading the mechanism. The magnification adjustment is provided with a releasable coupling so that manual adjustment of the magnification is possible for setting the same magnifications of the two telescope focuser systems of the binoculars. An adjusting method is concerned here. A prism arrangement for restoring image orientation is provided behind the axially displaceable lens L  12  for adjusting the magnification. A compensation group is arranged behind the prism arrangement, and is displaced in the axial direction together with the lens for changing the magnification. A diaphragm and an eyepiece are arranged after the compensation group.

 

 

 

 

 

Double that measurement. The length of the two tubes should be about this long.Fasten the larger lens on one end of the wider tube. Hot glue is good for this.Mount the smaller lens at the opening of the smaller tube. This is the eyepiece.Build a gasket from cardboard or Styrofoam if the tube opening is larger than the lens.Make sure the lenses line up with each other. The centers should be in the centers of the tubes and the Achromatic Lenses should be parallel with each other.

The object of the invention is attained by a telescope with an optical axis established by the optical elements of a telescope, including an eyepiece, an objective, and a first focusing optics, which is mounted displaceably along the optical axis for focusing, wherein the telescope has a second focusing optics, which is mounted displaceably along the optical axis for focusing. By the measure that a telescope is to be provided with a first and a second focusing optics, the focusing range of the telescope could be increased. A first focusing range is established by the first focusing optics, and a second focusing range is established by the second focusing optics; by the mutually adjacent existence of these two focusing ranges, the magnification of one of these two focusing ranges results. The first and the second focusing optics are mounted displaceably along the optical axis. Focusing can be effected by displacement of the first and/or the second focusing optics along the optical axis.

It is provided in an advantageous embodiment that the objective Achromatic Lens group is adjustable to preferred positions by means of detents. The user can thereby rapidly change by a predetermined amount between predetermined focus planes by displacing the position of the objective lens group by a predetermined amount. Furthermore, a region in which continuous displacement of the objective lens group is possible can be provided between the preferred positions. Stops are allocated to the displacement of focusing by means of the objective lens group, and signal a displacement by a predetermined amount to the user.

A lens series for Apochromatic refractors having a plurality of lenses positionable at each of more than two positions spaced along an optical axis and a reference plane at one of the positions which comprises, the plurality of lenses being positionable at the reference plane including a zero power lens having the same index of refraction, having the same thickness, having the same radius on one surface and the same distance to other lenses on the optical axis.This invention relates to refractor optical systems and, more particularly, to a spherical and a cylinderical lens series for a refractor having regular additive errors to permit non-additive combinations for correction of additive error.

Apochromatic telescopes are more expensive than reflecting telescopes, but they require less maintenance and are extremely portable.Resolve to invest a fair bit of money in this telescope. You can easily spend $1,000 per inch of aperture on an apochromatic refractor - without the tripod.Accept that the lower-cost models have limited light-gathering power and suffer from chromatic aberration. Chromatic aberration is color fringing around the object you are viewing.As refractors developed and became more refined, the disc containing the "weak" lenses were mechanically coupled to the disc containing the "strong" lenses. This permitted the practitioner to operate a single control to vary the spherical power presented to the eye and similarly a single control to vary the cylinder power presented to the eye. The constrictions placed upon lens design were even more severe in such instruments because the mechanical linkage used to couple the cylinder lens discs prevents the practitioner from personally selecting individual lens combinations.

Know that apochromatic telescopes use three or four lenses to eliminate chromatic aberration. This is the main reason they are so expensive.Refractors are well known ophthalmic instruments used for determining the proper lens value necessary to correct the defective vision of a patient. The refractor typically includes a right hand battery and a left hand battery, each for enabling the practitioner to place various corrective lenses in alignment with a respective patient's eye. Each of the batteries is alike and each includes a series of spherical lenses and series of cylindrical lenses. The spherical lens assembly and the cylindrical lens assembly each conventionally include a pair of discs. One of each pair of discs contains lenses having a "weak" power in incremental increases of power and the other disc of each pair contains lenses having "strong" power. The lenses of the "strong" power disc are of sequentially increasing power with the increments of increasing power usually at least being equal to the highest power of the corresponding "weak" lens plus the "weak" lens increment.

The practitioner may rotate one of the lenses in each disc into alignment with the patient's eye. In early refractors, like trial lens sets, the practitioner could select the particular combination of lenses which he wished to place before the patient's eyes. Each lens was manufactured to have a specific power whether the lens was used by itself or in combination with one or more other lenses. For example, to provide a cylinder power of plus 6.50 diopters, the practitioner would select the +6.0 diopter sphere lens and the +0.5 diopter cylinder lens. In lens series of such prior art devices, the designer attempted to minimize the error in any particular combination since each lens, for example, the +0.25 diopter cylinder lens, was used any time the practitioner needed to add 0.25 diopter of cylinder. In the average trial lens sets, there are over three thousand lens combinations in which the 0.25 diopter cylinder lens may be used. Since the only way to correct for additive error was to refer to a reference chart which covered all the permutations of lens combinations, the lens designer attempted to minimize the error resulting from combining lenses in each possible combination of the series.

Enjoy the advantage of an apochromatic refractor , which is never having to say the word "collimate." This type of telescope comes pre-assembled from the factory with all of its optics aligned.Enjoy that this type of telescope requires little care and maintenance.Plot your subject with the use of star charts.Position your telescope for viewing.Aim the telescope at the sky and find your subject.Position your eye over the eyepiece and focus.

A refractor singlet lens series, where all lenses presented at the reference plane (called the A lenses) have the same glass or plastic, the same thickness, one surface having the same radius and the same spacings to the next combined lens, will not change the additive error for a combination of three or more lenses when the A lens of the combination is changed. It is understood that, if the series of A lenses contains a zero power position, this position must have a zero power lens meeting the same requirements as any other A lens. Since the amount of significant additive error remains unchanged in spite of changes in the A lenses, the number of different corrections in all possible lens combinations which must be calculated or are required is reduced by a factor equal to the number of A lenses. Although the constant radius of the A lenses need not be infinity, a planar surface is preferred since the planar surface reduces the problems associated with constructing a zero power lens (window) to a minimum. The lenses at the reference plane may be made of either glass or plastic since the critical property is index of refraction in the composition of the lens material. As long as all lenses have the same index of refraction, they could even be a mixture of glass and plastic. Also, lenses other than those at the reference plane can be either glass or plastic.

The radius of the surface closest to the eye must be individually determined for each lens based upon the spacing of the lens from the eye and the power desired. While not constant, the radii for all lenses in a single dial will be related, since the spacing thickness and index of refraction for all lenses in that dial are identical. The lens series of the present invention when incorporated into a Apochromatic refractor manufacturer reduces the prior art additive cylinder errors in a refractor having 12 positions of the strong sphere dial by a factor of 12 and provides 100% predictability of the occurrence of significant additive errors since every position of the strong sphere dial has identical errors.

The drawing is an optical diagram illustrating the position of representative lenses in a refractor having a lens series of the present invention.

Name:SCT Crayford Focuser
Item No.: CF001
Description:

  Designed to last a lifetime and work with virtually any standard SCT/MC telescope focuser . Now you can enjoy zero image-shift during your most critical observations and imaging. Unbeatable in both quality and price.

  

Features

· 2" Focuser for Schmidt-Cassegrain / Maksutov-Cassegrain telescopes

· Crayford design: zero image-shift and focusing made easy!

· Very smooth, no lateral movement or tilting.

· The focuser tube is fully threaded and the threads are painted flat black to prevent unwanted reflections.

· Drawtube tension adjustable to match varying accessories .

· Included in the price is a 1:10 dual speed microfocuser, particularly appreciated during astrophotography.

· Black Anodized.

· Completely, precisely machined out of solid aluminum.

· 2" to 1.25" adapter with brass compression ring included.

· Internal anti-reflection threading on drawtube and 1.25" adapter to improve image contrast. 

 

Specifications

 

Focuser tube travel	25mm
Focuser tube length	115mm
Minimum distance from OTA to end of focuser tube (1-1/4" adapter)	95mm
Maximum distance from OTA to end of focuser tube (1-1/4" adapter)	120mm
Focus knob diameter	40mm
Weight	750g                 source:intane

The present invention relates to an achromatic lens system which is to be used in optical systems for telescopes, microscopes, cameras, video cameras, etc., and an image pickup lens system which comprises an achromatic lens system.
An optical system which is to be used in telescopes, microscopes, cameras, video cameras, etc. generally has a composition in which a large numbers of lenses are combined for enhancing optical performance of the optical system. A cemented achromatic lenses which is referred to as an achromat is frequently used in optical system for correcting chromatic aberration in particular. This achromat corrects chromatic aberration ordinarily for rays having two wavelengths such as the C-line and the F-line, but does not strictly correct chromatic aberration for rays having different wavelengths such as the g-line, thereby allowing chromatic aberration which is referred to as the so-called secondary spectrum to remain. This residual chromatic aberration often poses problems in objective lens systems for telescopes and microscopes as well as telephoto lens systems for cameras and so on in particular, and a lens system which is made achromatic for three wavelengths and is referred to as an apochromat is used for correcting the residual chromatic aberration.

Whether you're using it for school, work or a hobby, a microscope is a significant investment. It is important to find a microscope that will deliver exceptional performance, be easy to use and last for many years. Anything less is a waste of your time and money. As such, you'll want to learn just how to shop for a microscope.
Look for microscopes made of metal or a metal alloy. These microscopes are usually quite sturdy and last the longest.
Choose fluorescent lighting over incandescent. Fluorescent lighting is not nearly as hot as light from an incandescent bulb. The heat from incandescent lighting can sometimes kill small organisms on a slide.

A primary object of the present invention is to provide an achromatic lens system which elaborately corrects the secondary spectrum of chromatic aberration with a small number of optical elements.

The achromatic lens manufacturer according to the present invention comprises a radial type gradient index lens (radial type GRIN lens) whose refractive index varies in a direction perpendicular to an optical axis and a diffraction type optical element (diffraction type lens), and is characterized in that it satisfies the following condition (1): 0.1<θ e1gF <0.5 (1)

The achromatic lens system according to the present invention is characterized in that it satisfies the following condition (2): 67<V e1 <370 (2)
Pick an eyepiece with a wide field opening of at least 18 mm. The large opening in a large field eyepiece will cause less eyestrain than looking through a tiny opening.
Select an achromatic lens . This type of lens is designed for color correctness, meaning it will allow you to see all colors of the spectrum through it. A lens that is not achromatic may not let you see certain colors when you look through it.

Choose a microscope with a Deutsche Industrie Norm (DIN) lens. This is the most common type of microscope lens, making it easily replaceable by most microscope dealers if it should get lost or broken.Get a microscope with fine focus. Not every microscope comes with this feature. Fine focus allows you to hone in on details of a specimen that may otherwise remain unseen.
Shop for a microscope with metal focus gears. Gears made from any other material will break easily and wear out quickly.

The prism has long been one of the very basic optical components in many optical systems. It is a very fundamental optical component for many applications such as altering beam direction, zooming, correcting anamorphic aberration and correcting line of sight errors. The applications also include infrared detection, head-up display (HUD), helmet mounted display (HMD), laser radar, commercial cinematography, etc. Unfortunately, the generic dispersion characteristics of a prism limits its applications. That is, because of the variation in index of refraction and dispersion with wavelength, prisms are often not useful in applications involving a wide spectral range of optical radiation. These dispersion characteristics result in optical chromatic aberrations, that is, a departure of the image-forming system from the ideal behavior occurring when a beam passes through a system. In particular, prisms are prone to chromatic aberrations which results from the variation in the index of refraction with wavelength. Chromatic aberration will severely degrade the image quality of an optical system.

However, aberration of an optical component has both a positive and a negative contribution, and if these contributions are balanced, the total aberration of the system can be tolerably small. For example, Achromatic Lens and apochromatic prisms take advantage of this approach. Achromatic prisms, which correct for two wavelengths, consist of a pair of prisms with different dispersion coefficients and different prism angles. Apochromatic prisms, which correct for three wavelengths, usually employ two pairs of prisms with at least three different glass materials. While apochromatic prisms attempt to balance the positive and negative contributions to chromatic aberration they still have a number of drawbacks. For example, the residual chromatic aberration is generally larger than desired. Also, both achromatic and apochromatic prisms, because of the different prism components and materials, are generally bulky, complicated and expensive.

 

 

 

 

 

 

Thus it would be desirable to provide achromatic prisms and apochromatic prisms with a simplified construction. It would also be desirable to provide achromatic and apochromatic prisms having improved performance with extremely small residual chromatic and anamorphic aberrations.

Resolve to invest a fair bit of money in this telescope. You can easily spend $1,000 per inch of aperture on an apochromatic refractor - without the tripod.
Accept that the lower-cost models have limited light-gathering power and suffer from chromatic aberration. Chromatic aberration is color fringing around the object you are viewing.
Know that apochromatic telescopes use three or four lenses to eliminate chromatic aberration. This is the main reason they are so expensive.

In accordance with the present invention an apochromatic dispersive optical element comprises a first prism having first and second faces that form a first prism and a second prism having third and fourth faces that form a second prism angle. The second face of the first prism and the first face of the second prism oppose and are parallel to each other. A grating is disposed on to either the first face of the first prism or the fourth face of the second prism, and has a predetermined grating period such that the primary and secondary angular spread for a given spectral band is approximately zero. As a result of the unique properties of both a prism and a grating, achromatic and apochromatic prisms having a minimal amount of residual chromatic and anamorphic aberrations can be constructed.

Enjoy the advantage of an apochromatic refractor , which is never having to say the word "collimate." This type of telescope comes pre-assembled from the factory with all of its optics aligned.
Enjoy that this type of telescope requires little care and maintenance.
Plot your subject with the use of star charts.
Position your telescope for viewing.
Aim the telescope at the sky and find your subject.

 

 

 

Astronomical objects are what telescopes were made for and the Moon is one of the most telescopically viewed objects in astronomy. On a clear night a person needs little to see the details of a full moon. Now take an amateur telescope and visit the moon. As you enjoy your new view consider that with this type of telescope all you really get is a nice moon viewer. If the astronomer in you is excited by views of the moon, realize that it's just a quick to the apochromatic telescope store for a Newtonian type scope that can take you deep into space, as deep as the alignment of the primary and secondary mirrors is good. Collimation of the primary and secondary mirrors of a Newtonian telescope is imperative or you may just have gotten a bigger, more expensive moon viewer without the knowledge of how to collimate (align) dual mirrored telescopes (Newtonian).

An automatic focusing telescope capable of automatic focusing. This automatic telescope focuser includes object lens means for forming an inverted image of an object, ocular lens means for observing the image formed by the object lens means, erect prism means having a plurailty of reflective surfaces and arranged between the object lens means and the image of the object to erect the inverted image, semitransparent surface means formed on one of the plurality of reflective surfaces of the erect prism means to branch the light ray from the object lens means into a transmitted light path and a reflected light path, auxilary prism means arranged on the transmitted light path from the semitransparent surface means and having an exit surface perpendicular to the transmitted light path, focal point detecting means for receiving the image of the object formed in one of the light paths branched from the semitransparent surface means to detect the focal point thereof, and drive means responsive to a signal from the focal point detecting means to move at least one of the object lens means and the ocular lens means to adjust the focal point.

Bring the telescope outdoors to adjust to the climate outside before collimating the primary and secondary mirror diagonal of your Newtonian telescope. Temperature is one of nature's ways of inhibiting the performance of an optical mirror inside any telescope. The mirrors must be brought to a temperature that matches the outside atmosphere before any adjusting can be made.

Point the telescope to one of the early night starts for the first alignment inspection. Looking through the eyepiece into the telescope and out at the star, bring the star into focus and then out of focus so that the light of the star grows and becomes out of focus. Grow the light of the larger, but not so large that the light becomes diffuse and no edges of the light circle can be seen. In this light of the unfocused star should be a dark circle and the circle should be in the center of the light. This dark spot is actually the reflection of the secondary mirror. A dark spot that is not centered is not aligned and means you need to collimate (align) a dual mirrored (Newtonian) telescope.

Adjust the secondary mirror at the base of the Newtonian telescope using the locking and adjusting screws located in the protector ring of the secondary mirror. Loosen the Phillips head screws to be able to adjust the position of the secondary mirror diagonals with the Allen head screws. Screw one Allen head screw in and one out to manipulate the position of the secondary mirror. After each adjustment you will have to tighten the Phillips head screws and inspect the location of the dark spot in the light of an out of focus star. When the spot is centered the mirror is collimated. Next move to the primary mirror to get the best results of a Newtonian telescope that has been adjusted and aligned during use.

Remove the protective rim at the end of the telescope tube to reveal three clips that hold the primary mirror in place. The object of aligning a primary mirror is so that the center of the mirror, where the most focus comes from, is pointed directly at the properly aligned secondary mirror. The object is to be able to look into the focuser with no eyepiece in it and be able to completely see the primary mirror and its three retaining clips using the secondary mirror located inside the telescope. Viewed through the focuser without an eyepiece, the primary mirror needs to be adjusted until it can be seen completely, including the three retaining clips.

Return all protective collars and covers to the telescope after collimating the mirrors. By now the night is dark and the telescope is ready to be pointed deep into space. Look for Saturn, Jupiter, or Jupiter's moons. Now that you know how to collimate (align) a dual mirror diagonal (Newtonian), you can go and see far away astronomical objects with clarity.

In an example of binoculars disclosed in FIG. 1 of this publication, the light ray from an objective lens is divided into a transmitted light ray and a reflected light ray by a semitransparent reflecting mirror composed of a plane-parallel plate so that the transmitted light ray is used as an observation light ray and the reflected light ray is used as a focal point detecting light ray. The transmitted light ray forms an erect image through an erect prism system so that this erect image is expanded and provided for observation by an ocular lens. On the other hand, the reflected light ray from the semitransparent reflecting mirror is directed toward an automatic focusing module so that in accordance with a detection signal of the automatic focusing module, the ocular lens is moved so as to bring the forward focal surface of the ocular lens into coincidence with the focal surface position of the objective lens, thereby effecting the focusing.

Also, in the example shown in FIG. 2 of the above-mentioned U.S. Pat. No. 4,293,187, the light ray from an objective lens is divided into a transmitted light ray and a reflected light ray at a semitransparent reflecting surface provided on an erect prism system so that the branched transmitted light ray is directed to an automatic focusing module.

With the above-mentioned conventional automatic telescope focuser , however, if the plane-parallel plate (the semitransparent reflecting mirror) is arranged midway in an imaging system for the purpose of branching the light ray to the automatic focusing module, the plane-parallel plate is arranged obliquely with respect to the optical axis thus giving rise to a serious problem that a considerable astigmatism is caused to the transmitted light ray thereby making it impossible to observe a sharp image. This problem is particularly manifested in such case where the focal length of the ocular lens is reduced in an attempt to increase the magnification.

On the other hand, where the light ray is divided by the semitransparent reflecting surface formed on the erect prism system without using the plane-parallel plate, the transmitted light ray is naturally refracted greatly. In the case of FIG. 2 in the previously mentioned U.S. Pat. No. 4,293,187, the reflected light ray from the semitransparent reflecting surface is used as a light ray for observation purpose thus causing no problem as astigmatism in the observation system, whereas in the automatic focusing system using the transmitted light ray a considerable astigmatism is caused and the automatic crayford focuser is deteriorated considerably.

 

 

Whether you're using it for school, work or a hobby, a microscope is a significant investment. It is important to find a microscope that will deliver exceptional performance, be easy to use and last for many years. Anything less is a waste of your time and money. As such, you'll want to learn just how to shop for a microscope.

A diffractive-refractive achromatic lens that has a positive resultant power includes a refractive lens system and a positive diffractive grating. The refractive lens system is provided with a positive lens having relatively small dispersion, a negative lens having relatively large dispersion and an additional refractive lens. The additional refractive lens is a positive lens. The refractive lens system exhibits longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of the refractive lens system decreases as the wavelength becomes shorter. The positive diffractive grating corrects the longitudinal chromatic aberration of the refractive lens system. The condition 0.005<f/fD<0.2 is satisfied where f is the focal length of the entire lens system, and fD is the focal length of said positive diffractive grating.

Pay attention to achromatic lens ,when you shop:
1.Look for microscopes made of metal or a metal alloy. These microscopes are usually quite sturdy and last the longest.
2.Choose fluorescent lighting over incandescent. Fluorescent lighting is not nearly as hot as light from an incandescent bulb. The heat from incandescent lighting can sometimes kill small organisms on a slide.
3.Pick an eyepiece with a wide field opening of at least 18 mm. The large opening in a large field eyepiece will cause less eyestrain than looking through a tiny opening.
4.Opt for a binocular eyepiece. These eyepieces allow you to look at your specimens with both eyes (rather than a monocular eyepiece, which only has an opening for one eye). Using both eyes gives you better focus and minimizes eyestrain.
5.Select an achromatic lens. This type of lens is designed for color correctness, meaning it will allow you to see all colors of the spectrum through it. A lens that is not achromatic may not let you see certain colors when you look through it.
6.Choose a microscope with a Deutsche Industrie Norm (DIN) lens. This is the most common type of microscope lens, making it easily replaceable by most microscope dealers if it should get lost or broken.
7.Get a microscope with fine focus. Not every microscope comes with this feature. Fine focus allows you to hone in on details of a specimen that may otherwise remain unseen.
8.Shop for a microscope with metal focus gears. Gears made from any other material will break easily and wear out quickly.

 

 

 

 

 

 

 

The present invention relates to an achromatic lens to be used as a collimator lens, or an objective lens for a apochromatic telescope . Particularly, the present invention relates to a diffractive/refractive achromatic lens that includes a refractive lens system provided with a diffractive grating.

Conventionally, an achromatic lens has been well known and used as a collimator lens or an objective lens. An example of the achromatic lens employs two thin lenses: one being a lens having large positive power that is made from crown glass having relatively low dispersion; and the other being a lens having small negative power that is made from flint glass having relatively high dispersion. The resultant power is therefore positive, while the dispersion is neutralized.

Since optical glass has dispersion such that refractive index thereof increases with decreasing wavelength of light, a positive refractive lens has longitudinal chromatic aberration where a back focus of the lens decreases as wavelength becomes shorter. The achromatic doublet corrects the chromatic aberration of the positive lens by using a negative lens that has opposite chromatic aberration.

The conventional Aspherical Doublets is designed for correcting the longitudinal chromatic aberration with respect to two different wavelengths, e.g., F-line (486 nm) and C-line (656 nm). That is, the light beams of F-line and C-line are focused on substantially the same focal point.

However, light beams having wavelengths except the C- and F-lines are not focused on the same focal point. Particularly, the back focus of the doublet becomes remarkably larger in a range shorter than F-line. This remaining chromatic aberration is called as secondary spectrum.

If the normal optical glasses are used for constituting the conventional type of the achromatic lens, it is impossible to correct the secondary spectrum sufficiently. Because refractive index of glass increases as wavelength becomes shorter as described, while increasing degree of the flint glass is larger than that of the crown glass in short wavelength range. Then the chromatic aberration of the doublet is overcorrected (backfocus becomes too long) in the range shorter than F-line.

In order to suppress the secondary spectrum of the longitudinal chromatic aberration with the conventional type of the achromatic lenses , fluorite or anomalous dispersion glass should be used. However, these materials are too expensive.

It is therefore an object of the present invention to provide an achromatic lens., which is capable of correcting the secondary spectrum of the longitudinal chromatic aberration without using expensive material such as the fluorite or anomalous dispersion glass.

For the above object, according to the present invention, there is provided a diffractive-refractive achromatic lens that includes a refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of the refractive lens system decreases as the wavelength becomes shorter, and a positive diffractive grating for correcting the longitudinal chromatic aberration of the refractive lens system.

The Mewlon Series of Dall-Kirkham Telescopes by Takahashi combines refractor-like performance in a larger folded optic reflector design. The standard EM-200 or optional NJP mounts provide a stable, accurate platform for the M-210. The integral polar alignment telescope and R.A. axis level make accurate polar alignment to within 2 arc minutes of the celestial pole quick and easy. The reticle is designed to be used in either Hemisphere until the year 2030. No other manufacturer uses such a highly accurate polar telescope. The Mewlon series of Dall-Kirkham Cassegrain telescopes from Takahashi offer the experienced observer a level of performance and portability not found in other Cassegrain apochromatic telescopes mass produced for amateurs. The classical Cassegrain telescope offers excellent performance, but they are extremely expensive to produce at large apertures. By concentrating on the Dall-Kirkham Cassegrains, the Mewlon telescope offers a professional level of performance within reach of most amateurs.

The Takahashi Mewlon employs an ellipsoidal figure on the primary mirror and a spherical figure on the secondary. By focusing on very tight tolerances for these surfaces, Takahashi is able to deliver a compact telescope with reasonable aperture and high resolution. Where fast F/ratios are not required, the F/12 Mewlons provide excellent contrast by utilizing a smaller secondary mirror than comparable Cassegrain designs. Secondary obstruction as a percentage of diameter is 29-31% on the Mewlons. Classical Cassegrain telescope focusers usually have secondary obstruction of 32% or greater. Commercial Schmidt-Cassegrains have secondary obstructions of approximately 38% for F/10 systems. Ritchey-Chretien Cassegrains have even more secondary obstruction making them less suitable for visual, high contrast applications.

Takahashi uses extensive knife-edge baffling to minimize stray reflections as well as a specially designed tube that also acts as a light baffle. The result is an instrument that rivals an excellent long-focus Newtonian or refractor for contrast and sharpness. Some opticians have criticized the Dall-Kirkham design as having unacceptable coma. With most eyepieces (including Panoptics and Naglers) the coma is negligible and well outside the field of view. Stars are much smaller and sharper than in commercial Schmidt-Cassegrains. Coma may be a problem for wide-field astro-imaging, but these instruments were not designed for such tasks. With Takahashi’s field flattener/reducer, these instruments offer superb off-axis images at F/9.

Takahashi produces precision optical surfaces capable of delivering an airy disc of 20. Because the Mewlon mirror diagonal is larger than the effective aperture, its cell installation engineering helps to eliminate mirror stress which can cause astigmatism. The focuser mechanism has also been carefully designed to reduce shifting and maintain consistency. Both the Mewlon 250mm and 300mm models come standard a secondary mirror translating focuser that’s accomplished with the electronic hand controller. With a wide range of both visual and photographic accessories available to the Takahashi Mewlon series, there is no reason why you shouldn’t be able to achieve any astronomy project you have in mind using this fine telescope.

The 250mm and 300mm Takahashi Mewlon electronic focusing is accomplished by moving the secondary mirror. This eliminates the image-shift problem inherent to commercial Schmidt-Cassegrains with moving primary mirrors. Because of the loose tolerances required in moving large and heavy mirrors on a baffle tube, most SCT’s will not maintain perfect collimation. Image quality is then compromised in such optical systems. The large Mewlons also have removable covers for their primary mirror cells, this facilitates rapid mirror diagonal so that the observer can take advantage of favorable seeing conditions more quickly. These features make the large Mewlons ideal for high-resolution CCD imagery.

With the Mewlon series, it isn’t necessary to sacrifice optical performance for ease of use and portability. When it comes time to place your Takahashi Mewlon telescope on a mount, it’s as easy as simply connecting the dovetail plates. The high quality finderscope not only lends itself to the packages as an excellent instrument for alignment, but is also designed as a convenient “grab handle” to assist in mounting and transport. It’s rigid construction means help in handling the optical tube without fear of bending or breaking. On larger models, the Mewlon also includes a counterweight against the body to help balance the optical tube. Just these small considerations in Takahashi’s Mewlon design mean quality in engineering that sets it apart.

The 8.3″ Mewlon 210 weighs just 18lbs (8.2kg) with a 7×50 finder attached. The Mewlon 250 weighs only 28lbs (12.7kg) and is remarkably compact for a 10″ Cassegrain. Both of these instruments are highly portable and offer deep sky views that are exceptional. On the planets, many observers have reported seeing details they thought impossible with telescopes of this aperture. With the exception of a few diffraction spikes around bright stars, on might believe they were observing with a large apochromatic refractor . The advantage, though, is a greater amount of light grasp and resolution than a comparably priced refractor. Indeed, the Mewlons offer an exceptional value in their aperture class.

So if you desire a professional grade instrument in a compact, lightweight package or are tired of compromising light grasp for crisp detail and contrast, check out the Mewlon Cassegrains by Takahashi. You will be pleasantly surprised by their performance.

Features of Takahashi Mewlon 210 Dall-Kirkham Telescope OTA

    * Dall-Kirkham Telescope combines refractor-like performance in a larger folded optic reflector design.
    * The Takahashi Mewlon 210 at prime focus provides a focal length of 2415mm, focal ratio of f/11.5 and image circle of 18mm.
    * Primary mirror diagonal measures 220mm (f/2.9) with a secondary mirror amplification of 65mm (4X) and secondary obstruction of 0.32 (31%).
    * The Takahashi Mewlon 210 measures 700 mm long, 244 mm in diameter and weighs 17.6 lbs. (8kg).
    * It offers a limiting visual magnitude of 13.4 and a light grasp of 900x - providing an outstanding resolution factor of .55 arc seconds.
    * The Takahashi Mewlon 210 with optional reducer can achieve a focal length of 1961mm, focal ratio of f/9.3, image circle of 39mm and a 1.2 degree image field.

 

 

from:scopecity

A standard achromat (lens design)Apochromatic refractor will always show some color fringing on the edge of the moon and the cheaper the achromat refractor telescope, the more color fringing seen. Have seen some cheap refractor telescopes that produced so much color fringing that the moon looked like it had rings. To cure this shortcoming of the refractor design requires an apochromat refractor. A good APO refractor gets the job done, but it will cost you, dearly. Happy to report that my new 80mm APO telescope with its LOMO optics produced no color fringing.

In order to see faint celestial objects, or if you want to look closely at the moon and the other planets of our Solar System, you need a telescope. It important to know that while magnification can seem like a good thing, the important issue to consider when looking for a telescope is aperture - the diameter of the telescope focuser . The larger the aperture, the more light can be seen. Some rules of thumb:

    * Aperture dictates how much light can be seen
    * Focal length is the length of the refracted or reflected light path at focus
    * If you will take your telescope to remote locations, consider carefully your choice of aperture - weight considerations
    * Short focal lengths equal brighter images - not recommended for looking at planets (image too washed out)
    * Shorter focal lengths also equal larger field of view
    * Long focal lengths equal dimmer image and narrow field of view
    * NEVER USE A TELESCOPE TO LOOK AT THE SUN - without a proper solar filter.

A telescope’s eyepieces are often one of the most underrated parts of the optical system. Many folks get caught up with aperture fever or drool over high-end apochromatic refractors while neglecting the fact that the eyepiece is almost 1/2 the optical system!

Most telescopes include 1 or 2 eyepieces. Depending on the model and the manufacturer these might be junky, perfunctory eyepieces or decent lines like Plossls or Kellners. We’ll go over the various features of some of these “common named” lines as well as more modern designs.
These are more modern optical designs, without common names but rather brand names. These eyepieces are so numerous these days that we will describe them by their major features rather than by any names. New eyepiece designs are usually more expensive than the traditional designs as they involve more design and more glass elements.

So what telescope is best? There really isn't one, but there are some guidelines:

    * For an inexpensive achromatic lens , stay away from short focal lengths - anything greater than a focal length of f6.5 is good.
    * Apochromatic telescopes are very expensive, and just like high end audio equipment, have their faithful following. Read reviews and look for yourself! However, if you plan to use the telescope for astrophotography, an apochromatic telescope is necessary.
    * Meade and Celestron are the two main producers of the Schmidt-Cassegrain telescope. There is not a clear winner as to who is best, but Meade tends to include more electronic wizardry into their scopes - which is fine if you like that sort of thing. Truth is, competition between these two companies is good for the consumer as the need for better and cheaper telescopes are released often.
    * Go to a local Astronomy Club or "Star Party" - a gathering of like minded folks flocking to a dark location for a night of fun filled observing. There are sure to be a variety of telescopes, and most are willing to let you take a peek. Astronomy and Sky and Telescope magazines will have a list of national events.

The advice is to select a well-made telescope, of a design matched as well as possible to your primary observing interest and most frequent observing site. Make sure it’s a size that can be handled easily (by your standards and no one else’s) and used often, and you will enjoy a lifetime of awe and wonder under the stars!