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Example with a 90mm Maksutov-Cassegrain type scope (1 Viewer)

While things are a little slow (everyone playing with Christmas toys), I thought I would post another example of a photo taken with one of the small, relatively inexpensive Maksutov-Cassegrain type reflecting spotting scope/telescope. I was playing with my old Meade ETX-90 scope yesterday and took this photo of a pigeon. This is at prime focus with no eyepiece on the scope or lens on the camera. The ETX-90 is a 1250mm fl, f/13.8 scope. This was taken with a Nikon D40 at 800 iso. The photo is resized only with no post processing at all. This is a pretty slow lens, but with good reach without using any extra glass. Not perfect by any means, but pretty good for a scope that can be had used on ebay often for less than $200 in good shape. People on a really tight budget can experiment with this scope and still get some decent photos.

Rick
 

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Just wondering, can you get Mak Cass scopes with a better ( wider ) max aperture than F13.8 ?

Also, what type of glass are they .. ED, FPL53 etc ? Just thinking about the problems of CA with poor quailty glass. I dont know a thing about Mak Cass scopes, so i might be asking the wrong thing
 
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Just wondering, can you get Mak Cass scopes with a better ( wider ) max aperture than F13.8 ?

Also, what type of glass are they .. ED, FPL53 etc ? Just thinking about the problems of CA with poor quailty glass. I dont know a thing about Mak Cass scopes, so i might be asking the wrong thing

One of the major advantages of these scopes is the fact that they use polished mirrors to form the image instead of glass. This means there is practically zero CA, even with the cheapest scopes. These are also known as "mirror lenses". The image to my eye is not as high quality (contrast and sharpness) as my Celestron 80ED refractor...but it's pretty darn close and at twice the focal length. They do make these scopes in larger and smaller diameter models and some are faster. I have a Celestron C90 on the way that I picked up on ebay. It's a 1000mm, f11. We will see how it stacks up against the highly regarded Meade ETX-90.

Rick
 
Thanks Rick

Would a Mak Newt be comparable to a Mak Cass ?

Mak Newts have a smaller secondary mirror as a rule, and therefore tend to be somewhat better in terms of contrast. The primary mirror is actually slower than in a Cassegrain at around F6 (compared to about F3) and this also makes the mirror easier to fabricate and being slower, optical abberations are reduced.
Drawback from a birding/photographic perspective is that the focus assembly is at the front, near the corrector plate. Unlike Cassegrains where the secondary is typically an aluminized spot on the back of the corrector plate, the Newtonians have a separate adjustable secondary mirror (the primary is also usually adjustable). Not good in a portable/field situation as collimation is something that will have to be done frequently.
Also you dont get small Mak Newts-the smallest I know of has an aperture of about 130mm, with a tube length of perhaps 800mm.
 
Collimation is always a problem when used in the field but I would say manageable. The main thing is how the better "Mirrored" scope match up to the 80ED Refractor? Though the bigger "mirrored" scope may be broader but can be short and light. Being zero CA would be wonderful but how would it handle flare or back lit situation. Bluedubius, fight them out when your C90 arrived and in different situation to evaluate their performances.
 
Mirror scopes produce donut bokeh which can be really bad depending on the scene. They are fun to experiment with but the bokeh would always put me off owning one myself.

Paul.
 
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Mirror scopes produce donut bokeh which can be really bad depending on the scene. They are fun to experiment with but the bokeh would always put me off owning one myself.

Paul.

Always trade-offs to consider. I'm mostly putting this up because we occasionally have individuals asking about getting into bird photography with a very limited budget. Even with the donuts, I would rather have some nice CA free, sharp images (remember that pigeon is completely unprocessed) from one of these scopes as what I used to get when I first started with a 60mm, non-ED scope at the same or even higher price than a used 90mm mak. As far as image IQ, I do prefer my Celestron 80ED...but it's twice as heavy and two or three times the length...have to use a 2X converter to get to the same focal length...etc, etc. Sometimes I wish I only owned one scope, but I'm like you...I like to tinker :).

Rick
 
Mirror scopes produce donut bokeh which can be really bad depending on the scene. They are fun to experiment with but the bokeh would always put me off owning one myself.

Paul.

I wouldn't mind spending a little time with PS to swallow those donuts. But the IQ just doesn't seems to get me aroused (correct me if I am wrong). My Tamron SP500 Mirror been sleeping the last 6 months. About time I find him a new home.
 
This is very interesting, even if you are on a budget finding these on oboy could be cheap and if you looked after it a decided after a short time you dont want to keep it it is quite possible to get back what you paid on oboy - many a time I have done this and a few times made a profit.
 
This is very interesting, even if you are on a budget finding these on oboy could be cheap and if you looked after it a decided after a short time you dont want to keep it it is quite possible to get back what you paid on oboy - many a time I have done this and a few times made a profit.

So how do you find them? Any good? Wish I can do the same here...
 
The main problem with reflecting scopes rather than refractors, from my experience, is that they hve less contrast, and more glare when used terrestially, compared to a refractor. This is because of two main reasons. 1/.... a small decrease in contrast and resolution is caused because reflecting scopes necessitate a central obstructing mirror of varying types which interferes with the light beam, whereas a refractor does not and 2/....The main problem when used terrestially is that they are notoriously difficult to baffle from the expanse of daylight, often using long cone shaped baffles rather than a simple circular opening, and it is a very fine balance between stopping unwanted light entering the system and yet maintaining contrast and cutting out glare. Problem is always there, but does not matter so much when used for astronomical purposes because there is a minimum of light to cause the glare in the first place.Tom
 
Hi Rick, I have the Meade ETX 90 as well and only tried holding point and shoot camera up to the eyepiece, never tried prime focus. Very nice picture. I have used the ETX 90 during the day and spotting bullet holes. I do have the Celestron 80ED and Orion 100ED refractors.
Not much to photograph here, crows and it is cold.
 
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I wouldn't mind spending a little time with PS to swallow those donuts. But the IQ just doesn't seems to get me aroused (correct me if I am wrong). My Tamron SP500 Mirror been sleeping the last 6 months. About time I find him a new home.


Camera specific mirror lenses and astronomical Cassegrain style mirror telescopes aren't in the same league optically. While I agree that mirror lenses tend to leave much to be desired with regards to resolution, almost every astronomical Maksutov Cassegrain built in the last 30 years is 1/3 wave lambda or better, which means far higher surface polish quality than even the best professional grade camera lenses.

Additionally, and I'm actually not sure of the exact measurements, but looking at an image of a lens such as the Tammy SP-500, it appears that the central obstruction is close to 40-45% of the objective diameter. That much obstruction is contrast and resolution robbing. Mak Cass scopes seldom go above 35%, and some as low as 25%. With smaller sizes like this resolution is less impacted. While contrast may remain lackluster, we thankfully have plenty of software options to help correct this.

Touching on the comment by Tom (tjd) regarding glare and internal reflection, there in some validity. However a simple dew shield will remove most of the oblique angle daylight, thus improving contrast significantly.

I think the image is good, and that Rick's idea of passing this along for interested low budget birders is a valid one. Paul is correct regarding the donut shaped bokeh, obviously a product of the secondary mirror in the light path. It does make for some occasionally unpleasant bg's, but doesn't take away from use as a life list lens, or simply for learning long lens technique. Best of all is that you can just throw a diagonal and eyepiece in the back for use as a spotting scope.

Obviously no lens does everything perfectly, and every astronomical scope used for birding has it's own unique limitations. But for size, weight, resolution, and ease of use, I'd say small (90-130mm) Mak Cass scopes are a great option for starting birders.

Good post Rick. Thanks.
 
Informative post Jason. One thing that puts me off is the aperture of the Mak Cass being very poor, ( f13 ? ) even if the IQ is ahead of DSLR mirror lenses. Wouldnt a Mak Cass be usable in only the best of light conditions / bright sun day etc ?
 
Informative post Jason. One thing that puts me off is the aperture of the Mak Cass being very poor, ( f13 ? ) even if the IQ is ahead of DSLR mirror lenses. Wouldnt a Mak Cass be usable in only the best of light conditions / bright sun day etc ?

I would agree with your assessment wholeheartedly, Musoman. As it stands, I shoot with a lens that requires ƒ8.0 to maximize IQ. At 8.0 I typically need to ramp my ISO to 800 in good light, and 1600 in mediocre light. ƒ13 is 1 1/3 stops slower, which obviously requires pushing ISO, or accepting slow shutter speeds. The ISO thing is OK for me, since I can PP most of the worse noise out. But slow shutter speeds are often a detrimental risk for bird photogs, as everyone here already knows. I think BIF would be out of the question for most mirrored lenses. Although certain situations make perfectly good subjects, such as perched raptors against a blue sky.

I hope he doesn't mind my reference, but one of our BF members had dome some really nice digiscope work with a 127mm Mak Cass. His Bald Eagle images always impressed me, especially considering they are done with a Compact camera hand held to the eyepiece. A couple of examples:

Bald Eagle juvenile
Bald Eagle adult
Burrowing Owl
 
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