I am new to astrophotography. Until now I have only been using a Raspberry Pi camera and a self build equatorial mount. Now I would like to go a step further. I would like to keep my butget as small as possible and see how this hobby evolves. As a next step I woud like to buy a used DSLR from Canon. I think Canon is the right choice as I would like to use open software (on a Raspberry Pi) to controll the camera and my self build mount. In addition vintage lanses sound promising to me as they are relatively cheap and nearly all of them (except old canon lenses) are compatible using adapters.
I was adviced to keep my expenses as low as possible in this first (second?) step to have more more money later for real equipment. I heard that old canons are really noisy. I there a point in time where this changed or was it a gradual decrese? I am thinking about a 4 digit camera (like 1200D) or a 3 digit camera (like 700D) with about 18 MP. Is there a great difference beween cameras of the same line and the same pixel count? I have found assertions in some forums that some of these cameras have the same sensor. E. g. is a 700D (T5i) really better for my application than a 55D (T2i)?