Quote:
Originally Posted by JA
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.
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Hi JA,
Thank you very much for your reply, i was waiting, i so appreciate it.
I will give you points so it might help you understand better my issues and my plan and who knows, we might get somewhere or a choice or a conclusion based on those point, so here we go:
1. I used 300mm, a perfect lens, almost perfect FOV, but it is outdated and it has age problems, it needs service and i can't send it to any service, in my country all lenses services are super expensive for worthless payment, and i try hard to find someone to 3D print for me a lens cap for this 300 2.8 with the hood/dew shield so i can stop down the lens to something like F4 or F5, because i don't have a camera to change aperture to F4/F5 and i hate the spikes from lenses stopped down, never same as Newt/reflector spikes.
2. Focus is so critical with lenses, and the lens 300mm has problem with focusing ring, it is almost dead so i have to use force to focus, that will ruin my setup if i keep using force on the mount and entire setup, so i try to avoid doing this, also lenses have many elements or optics, this might affect sharpness for astrophotography, i feel scopes are straightforward and designed precisely for astro.
3. QHY163M isn't my only camera, it is my first ever cooled, i was thinking about selling it and go larger as APS-C mono, but the financial and situations showing me that this upgrade plan is far long time in future and i don't want to miss things right now, so i decided to keep it, i might buy APS-C mono separately without selling QHY163M.
4. I have 4 cooled cameras, 3 monos and 1 color, the color one is the only one in APS-C size, and i was planning to connect this to my new 90mm Triplet and adding 0.65x reducer or 0.6x, so i can go to that FOV i am looking for, in normal cases i can use the scope natively at 540mm or buying dedicated reducer for it and bring it to 432mm, but from some results i did last year by end of year [Nov-Dec] i can't get those FOV out of my head, and i did them only after i ordered 90mm few months earlier and i didn't cancel the order after that wait.
5. Main setup is dual imaging setup, 2 scopes and 2 cameras, so if i am thinking about pairing that APS-C OSC with 90mm and say 0.65x for example then that will leave one of my 4/3" cameras mainly my new one QHY294M Pro for a scope or lens in 270-290mm, and i found that Askar FRA400 with 0.7x giving 280mm is a perfect match for FOV, very slight difference, that Askar is quintuplet, so i can use without any flattener natively at 400mm or reduce it to 280mm, nice results i saw from this scope around, so if i get this then i am almost done there and it will be nice scope all around too, but someone told me to forge this scope idea which will complicate the plan and make me lost again.
6. From point 5 above, if i go with Askar FRA400 which will cost nearly $1100, then i will have little money/budget left, something around $400-600 maximum, i won't buy reducers by now, i will try to spend that budget i will get to get scopes first, making sure those scopes are the correct choices, then later i can add flattener or reducers with another budget later in future, so that i was asking about if i will choose that Askar FRA400 for example, then the left money i only have to buy smaller cheaper scope, such as 60s or 70s somewhere, i can't buy 90mm/80mm aperture scopes again and definitely not two FRA400, but i can just hold on my plan and go with only one scope to match my 90mm FOV reduced, but i don't want to keep 4 cameras like only 1 or 2 in use and the other 2-3 are collecting dust, and will not sell at this moment.
7. My mount is capable to hold two average weight/size setup or almost 3 small/average setup, 90mm with something like 60/70mm scope will not exceed or reach the payload capacity, those scopes are at 2-5KGs mostly as OTA alone, so i can say the three OTAs will max them out to nearly 10KG, then i am left with about 4-6kgs, cameras with and without filter wheel will match that, and with OSC camera i don't need a filter wheel, and i am planning to buy one more mount in future just in case, so i better get scopes now and worry about weight or another mount later, if my current mount can handle it then perfect, if not then i can wait and practice/use with two scopes and i swap one with another just to have both in use regularly, i done waiting stuff month after month or year after year, so i will buy anything or everything as soon as possible and i take my time using them one by one, my mount is allowing enough possibilities.
Sorry with long points, but i am trying to explain in depth as much as i can, if you have any further questions or points you want to ask me then i am willing to answer with all pleasure, i have to make clear good decisions as much as i can without sacrificing or selling my current equipment, i have very bad luck in selling stuff so i won't wait some miracle sales to buy again, and budget won't wait to be spent.
Best
Tareq