On the problem of astronomical telescope receiving SLR photography

In fact, in terms of focal length, it is still 900mm, and the lens angle of the contract focal length is the same. But because your lens aperture is only 80mm, the phase field will be very small, and such a small imaging circle has a dark angle on the SLR camera or can only produce a round image.

How many times is it enlarged? Hehe, the lens only said the focal length, not the magnification. The magnification of a telescope depends on the eyepiece. There are high power eyepieces and low power eyepieces, depending on your choice.