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Dumb Newbie Question!

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#1 Guest_**DONOTDELETE**_*

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Posted 03 April 2004 - 09:40 AM

Do Maks suffer from chromatic abberration? If not, is there anything else to be aware of when considering a Mak?

#2 jmoore

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Posted 03 April 2004 - 12:27 PM

No chromatic aberration in Maks.

As for what else to be aware of with Maks....

Positives:
1. long f/ratio makes good for high power viewing, and allows you to get good views with less premium eyepieces. Thus, Maks are considered good planetary/lunar scopes.
2. portable because of compact design
3. doesn't require frequent collimation

Negatives:
1. long cool-down time
2. long f/ratio means that widest FOV possible is relatively narrow compared to other scope/design with similar aperture. With an Orion Starmax 127, for example, the widest you can go is about 1 deg FOV. So...it's not the BEST design for panning around the skies, especially if you haven't learned to starhop very well yet.

Note...the pros and cons for any scope/design are relative. For example, long cool-down is not a problem if you have the foresight to put the scope outside while you're eating dinner. Simiarly, the 1-deg FOV limitation exists for any scope with 1500mm focal length or longer, including 8"+ SCTs, and 14"+ Dobs. Yet, big Dobs are considered DSO specialists. So, don't yet anyone tell you that a Mak isn't good for DSOs just because it doesn't have a wide FOV.

#3 Guest_**DONOTDELETE**_*

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Posted 03 April 2004 - 07:51 PM

...the only dumb question is the one you do not ask...

Mak-Cass or Mak-Newt? :)

I have a Mak-Newt (MN56) but it has a short FL and a relatively wide FOV (that's why I bought it).

I agree with Jmoore, the pros and cons are relative. I've seen the effects of not letting my mak-newt not cool down enough so I plan ahead and set it out early.

IMHO, a mak-newt or -cass is a good optical design. I've read many favorable reviews of various mak scopes.

-Dave

#4 wilash

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Posted 03 April 2004 - 08:38 PM

Maks are not 100% free of Chromatic abberation, but they control it so well they are considered "color free." Most color you see is caused by atmospheric refraction that affects all telescopes. The Maksutov design is excellent at minimizing all kinds of abberations including spherical abberation and coma.

There are two Mak designs - Maksutov Cassegrain and Maksutov Newtonian.

The Cassegrain design is the most common and has the eyepiece located at the back. They use focal ratios from f/10 to f/20 with f/15 being the most common. There are Mak Cassegrains which have f/6 and f/3 focal ratios, but are for imaging only. This design has more back focus and can be better suited to prime-focus FILM astrophotography than the Newtonian brother. However, many of the cheaper models will not illuminate the entire 35mm frame.

Maksutov Newtonians have the eyepiece located on the side at the front of the telelscope. The Newtonian design is usually f/6 and so can be used as a wide-field scope as well as giving high-power views. The central obstruction is also less than the Cassegrain design and so the scope has better contrast. Many people feel the image quality of the Mak Newtonian rivals that of an APO refractor.

The field of view in a telescope is primarily related to the scopes focal length, the longer the focal length, the narrower the field of view. To get the focal length of a scope, multiply the focal ratio by the aperture - a 127mm f/10 Mak has a focal length of 1270mm, a 160mm f/10 Mak has a focal length of 1600mm. Of course changing the eyepiece to change the magnification also changes the field of view, but the scopes focal length limits the range. For example of you have a 32mm and 8mm eyepieces and a 127mm f/10 Mak the magnification range is 40X and 159X. If the scope is a 127mm f/15 Mak, the range is 60X to 237X with those same eyepieces.

The focal ratio also limits the maximum exit pupil which is related to image brightness. To calculate the exit pupil, divide the eyepiece focal length by the telescope's focal ratio. A 40mm eyepiece used in an f/10 Mak has an exit pupil of 4mm. In an f/15 scope, the exit pupil is 2.7mm. An f/6 Mak Newtonian can have an exit pupil of 6.7mm with the same eyepiece. Also if the exit pupil is too small, it prevents your eye from forming an image. Using the F/10, F/15, and F/6 scopes, a 5mm eyepiece will create an exit pupil of 0.5mm, 0.3mm, and 0.8mm.

Then comes the problem of what you want to see - planets, Moon, double stars, nebula, galaxies. Each target has different requirements. Planets, Moon and double stars need magnification. The moon is very bright so can handle higher magnifications and the dimming of the image that comes with that. Whereas planets and double stars need high magnification but also brighter images. Large DSOs are easier to see at lower powers, partly because of the size, but also because of the brighter images from using longer focal length eyepieces.

Maks are great scopes. A Mak Newtonian is a great all round instrument. The Mak Cassegrain is also very good, but can be limited by its long focal ratio and focal length.

BTW, I have a 127mm f/10 Maksutov Cassegrain and love it.

#5 Guest_**DONOTDELETE**_*

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Posted 04 April 2004 - 01:38 AM

Thanks for those replies - superb information that even I can understand!


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