Mak Cass Scopes in the Day Time

At RGVECB, largely by coincidence we have 3 of these Maksutov Cassegrains (cats). They are a C90, a Lomo Astele 95 and a Lomo 133.5mm. We have the 133.5 mm mounted on a very heavy equatorial mount and have not used it much for terrestrial observation which is the subtopic here, terrestrial observation. We have used the C90 once for some semi-serious birding, at a big sit. At that time it was brand new. The only eyepieces we had then were a Celestron 32 mm generic plossl, 15, 20, 25 and 40 mm GSO plossls and 12.5 and 18 mm Celstron Xcels. The Xcels are way too big for the little C90, aesthethically, and one spends more time trying to figure out where to look in them than looking out of them. The astro boys can tell you all about blackout.

We have continued to fool around with all these eyepieces in all three scopes, and now we have more eyepieces to compare them with, for terrestrial viewing. What other eyepieces do we have now? Easy that: 30 mm Ultima, 25 mm Lomo plossl, 25 mm UO ortho, 20 mm Tele Vue plossl, 16 mm UO Konig, 12.5 UO ortho, 7 mm UO ortho and a 7-22 mm Apogee zoom. All thes eyepieces except the zoom were bought used at Astromart or on EBay. We also have an Atik 0.5 focal reducer which provides some interesting views in association with some of these eyepieces.

First the negatives on cats. All these negatives have been well-documented by other users, so if you know all this, skip ahead.

1) narrow field of view
2) annoying secondary mirror image that varies from slightly troubling to aggravating depending on the light and eyepiece, you nearly always have a shadow in the very center of the field of view
3) fairly heavy for a spotting scope and not as outdoorsy as dedicated spotting scopes
4) images are backwards or backwards and upside down unless one resorts to an erect image prism or a star diagonal and with the latter the image is still backwards
5) can't focus below 30x which makes it tough to find stuff
6) can't compare in brightness contrast to an ED refractor like a Pentax or the German ones

Solution and partial solutions

1) Atik focal reducer widens the field appreciably and reduces magnification. The 16 mm Konig is the only wide field eyepiece we have and it confers a wider field for terestial views. Others we suspect would work to do this too.

2) Th UO orthos and Konig, for some reason deal with this fairly well to the point that you can forget about it. Some of the other eyepieces are OK too under some light conditions. The GSOs, possibly becasue of their overdone green coatings don't handle this well and generally all the plossls do worse than the othos. This makes us wonder if we should get a UO Kellner or two.

3) After luggin that Lomo GEM mount around the little ones on altaz mounts seem feather light. I'd take the C90 anywhere I'd take an 80mm Leica or Swarovski cause I could buy 10 C90s for one of them. The little Lomo is more problematic because it does not pretend to waterproofing and is not armored. However, I suspect it might survive use as an artillery shell.

4) The C90 has a flip mirro which allows use of a prism diagonal with noticeable reduction of image quality, brightness and contrast. We got a deluxe prism from Stellarvue for the Lomo. It is nicely designed and seems to be optically better than C90 prism. Images are better too than in the C90 cause the Lomo is a little bigger scope with slightly better optics. In the Lomo, using a Tele Vue diagonal, and a 12.5 ortho, 96x is no sweat on terrestrial. This indicates why I am interested in these cats as spotters. And even the Lomo is really cheap compared to a decent refractor.

5) The Atik focal reducer (fr) really does work. For example, the 30 mm Ultima with the focal reducer inserted gives 20x and the image quality is pretty good even through a prism.

6) Which brings me to UO orthos and the Konig. These little guys, perfect matches sizewise for little cats are great for long distance spotting if you can find whatever you are trying to look at. The Konig FOV is better. Interesting. I'd like to compare the big ED spotters with the Lomo and UO orthos at 100 + x.

Another intersting eyepiece is the Apogee zoom. It's very handy and seems to be a simple design like an ortho. However at 7.3-22 it's not much count below about 15 (too dark)in the little cats, especially under low light conditions. I wanted to try it with the focal reducer, but of course the lousy zoom barrel, though threaded, is too big for the fr and also for Celestron filters. Go figure. I have contacted Apogee for an explanation. I suspect, however, that this zoom would work very well with the fr and give the cats a nice range of low power magnifications for scanning.

Soooooooo. If you want to do some spotting on a budget, get a Cat, some used UO Konigs or orthos, a focal reducer and maybe a zoom with standard size threads. You'll be set to run with the big dogs for about 400 dollars. Plus you can use yer scope at night for some nice planetary views.