There is Schmidt-Cas and matsukov-cas types.
They are very similar designs with similar performance. The main difference is the type of corrector lens plate up front. The cas used an
almost flat plate. The matsukov uses a heavily curved corrector that traditionally has been considered difficult to shape well. But with computer controlled grinding now days I don't think its much of a problem.
I considered both those mentioned scopes before making my recommendation. They are both good scopes. I've heard good things about both. But there are a couple of reasons I leaned towards the AR-5:
- Although both the above mentioned scopes are "sealed" systems, they also both have secondaries that will need periodic adjustment. The refreactor requires none.
- Since both the above scopes have secondary mirrors, the area blocked by the secondary has to be subtracted from the total light gathering aperture of the main tube. So a 5" reflector with a secondary doesn't gather as much light as a 5" clear aperture refractor. Plain and simple.
- When ever you have a central obstruction (like a scondary), it causes light to be scattered as it enters the tube. This is called diffraction. It will cause you to get a slightly less crisp image and will slightly washout and reduce the contrast of the image. A refractor has no central obstruction. You can focus star into much more pinpoint like sharp dots. You get a much higher contrast image.
- Both those scopes had equal or longer F/ratios as the AR-5 with no more aperture so they'd do no better or worse on deep sky stuff versus the refractor.
On the other hand, both those other scopes are "folded" light path so they fit into a shorter tube which is easier to mount stablely.
Still, my personal rule of thumb would be: anything approaching equal aperture and equal electronics I'd always choose the refractor.
However, you generally can't get a refractor over 6" without paying a king's ransom. However reflectors over 6" aperture are common. Shear aperture can overcome alot of design defficiencies.
I'd take a 5" refractor over a 6" schmidt-newt any day. Now a 5" refractor vs a 8" schmidt-newt is a much harder decision. Would I take a 10" newtonian reflector over a 5" refractor? Hmmm probably (with some caveats). But now you're talking much more than the $600 you told me I had to work with.
Watch it! Its a slippery slope that leads to a 12" monster!
I'd need to think about it some more to give a clearer opinion. However the first thing to look at is the mounting. That is where most dealers try to recover the cost. When they put that 10" on the same tripod they use for 6" and 8" then its prolly way to heavy for the mount. You'll have bad problems with vibration and general wobblyness.
You're getting close to the dollar amount where I'd start recommending a well made 8" Schmidt-Cas rather than a 10" newt or schmidt-newt. It'll be less maintainence and will prolly have a more stable mounting because of its shorter tube.
You're starting to see why I recommended joining a club and get a chance to try out a lot of different designs and sizes before making a decision. There are a lot of variables to balance.
Wab
