Quote:
Originally Posted by TareqPhoto
I want to buy a refractor for DSO imaging, and i want cheap small one, i have the choice between 60s aperture scopes or 70s aperture scopes, if 60s then simply i can add 0.8x reducer later and i will be fine, but with 70s aperture then i have to do one of two things, A: To buy a reducer such as 0.65x or 0.7x a must, B: Buy APS-C mono camera which is very pricey for now, but it can be a plan later anyway, So with two choices i have to be careful what should i buy, your opinion.
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I would choose neither. From the apertures you've nominated (60 or 70mm) and your desire to do DeepSky imaging using as you have said reducers, it's apparent that you are looking for something like a 300mm focal length (based on a 70mm aperture at
say f/6 with a 0.7x reducer =70x6x0.7=294mm), which you could then use with your QHY163 4/3" sensor which as a guide would give you a roughly equivalent field of view to a 600mm focal length on Full frame and if/when you decide to upgrade to an APSc sensor you would get a wider field of view: roughly equivalent to a 450mm focal length on Full frame. If those fields of view are too tight for you, you could scale down the lens to a focal length of ~200mm. There are many fine lenses you could choose from in the 200-300mm range, then it's simply a matter of adapting them to your camera/s, unless there are filter wheels involved as that brings more complexity, not that it can't be overcome.
So why go to all that trouble (scopes/reducers/flatteners/spacing etc...) if you want two ~300mm optics for <$500 each? I would simply look to some high quality full-frame camera lenses, something like 300mm f/4 or perhaps faster for more $. You also then don't have the problem/cost associated with needing buy and experiment with spacing etc for a reducer or flattener as these are typically part of the optics in camera lenses which are designed to image on to a flat plane.
Best
JA
BTW I seem to recall you already have(had?) a 300mm f/2.8 which you could possibly then use.