I'm trying to justify buying a 2-3 thousand dollar telescope for astro photography when I already have a camera and lenses costing 2-3 times that much. I'm looking for opinions on which way you would go in my situation.
So far I have a Canon 5D3 and a variety of "L" lenses to choose from for astro photography. (I also have a CGEM) So let's say I decide to use my 400mm f/5.6 prime lens attached to a 2X tele-converter giving me effectively an 800mm lens for AP. All things being equal, I assume that the image size at the camera sensor would be identical if I used a hypothetical 800mm telescope and mounted the camera at its prime focus. Let's ignore aperture for the moment because I understand that the larger aperture available on this hypothetical 800mm scope would give me a brighter image and therefore shorter exposure potentially. Am I thinking right so far?
The Canon 5D3 has a 22.3 megapixels on a full frame 24X36 mm sensor. That gives generous size pixels for collecting more photons without having to introduce too much electronic noise by multiplying the contents of smaller pixels in cropped frame cameras. What would I gain by adding a high end telescope to my present setup? Hanging that heavy camera at the prime focus of this high end scope would render it useless for simultaneous observing. As an alternative, eyepiece projection would give me the option of greater magnification of course. As far as I know dedicated astro cameras are pretty much all prime focus devices, so there would be no greater magnification available there - although they would be lighter in weight and potentially allow switching color filters. Of course I could also used a cropped frame camera instead of the 5D3 and get simulated magnification that way. Alternatively I could use a lesser quality scope for observing while letting the Canon take the high resolution images. Then too, there is the option of using a modified camera instead of the standard 5D3 to boost infrared response. So many avenues to choose!