[JimmyDranox]

There are some eyepieces used for projection, which have a T2 or M43/0,75 on the camera side like Baader Hyperion. But afocal photography is very rare used, despite is different magnifications, mostly because it can bring a lot of other problems, heavy vignetting, and low light.

The fact that the image is upside-down, is the smallest. Real good astro images are made after a lot of PP, not in only one program. Often, this means hours of work on computer to get one picture from a big number of raw images stacked together.

[pete-tarmigan]

I can't say exactly about this piece, but from my experience, adapters for spotting scopes have a different barrel than 1,25'' or 2'' which are standard for telescopes. What I can see from specifications, is that this adapter is in fact a projection lens. And with 12.5 fix aperture (focal/diameter ratio), and magnification included, I wouldn't recommend it for use with anything other than Pentax spotting scopes.

With the adapter set up I have described before, you will have the native F/D ratio of the telescope, which can be much faster for some of them. And you can modify it with the help of a Barlow lens.

What kind of mirror scope did you have?

If you're referring to me, I don't have a mirror scope (I have the PF-80EDA). I was bringing up the PF-CA35 in case it might be usable by the original poster.

The PF-CA35 has the same diameter barrel as the eyepieces for the Pentax PF-65ED, PF-80ED and PF-100ED scopes, i.e., the XW and XF series eyepieces, which have a barrel diameter of 1.25 inches.