Quote:
Originally Posted by janoskiss
The CA gets worse with aperture for a fixed f-number. I have not looked through one of these scopes but on paper it should have lots of CA. A naive paperless analysis tells me that you need to increase f-number in proportion to aperture. So eg a 75mm f/4 would have the same CA as a 150mm f/8, all else being equal.
You can tame CA with filters and in even more clever ways (but filters are the easiest and cheapest off-the-shelf solution). If you can easily afford the scope and you're curious to try it out then get it. You'll have fun with it and you'll learn stuff.  |
One of the other simple ways to tame CA on bright objects is to use an aperture stop. If the scope is stopped down to 120mm aperture then it becomes an f10 scope and if stopped down to 100mm it becomes an f12 scope. CA will be significantly reduced and the scope will still gather sufficient light from bright objects to give a well illuminated image. Combine this with a filter as mentioned and you will be quite surprised. Some cardboard, glue and some packaging tape is all you need to make some effective aperture stops to test the idea. have made a set myself and they work a treat.
Cheers
Steve.