058 is a solid investment Andy. Mine is working fine for years now. What price they're asking for?

Its old stock so £180 Rudra.

I'm not keen on mirror lenses at all but I do have one that I think is worth considering instead of the Nikon 1000mm f11...The Russian MTO 1000A 1100mm f10.5...It offers a 100mm FL advantage yet its a wisker faster than the Nikon and its bound to be a lot cheaper too.

As a result, a lens with a focal length of 1000mm has a physical size of about 30 cm in length. This complicates the process.

You only have to move the focus ring a fraction of a degree to change the focus by many feet!

Although the thread is nearly ten years old, I think it only fair to point out this is actually the case for all lenses at the more distant end of the focus scale. Adjusting focus from distant stars to the moon (more miles than you can comprehend) hardly needs any focus adjustment at all :) In my experience the degree of focus movement with a mirror lens is not that different to a refractor of similar focal length. The design of the thread on the focusing helicoid being chosen to make it match the focal length. There is a range of focus sensitivities, some lenses giving more focus movement than others AF lenses tend to have less movement for a given change in focus, as precision in manual focusing is not so much of an issue.

Ohhhh Gush and this is an old thread with some earlier questions directed at me, when I never saw. So awfully sorry for that.

Yes "Petrochemist" and focusing with these (CAT lenses), in general is not difficult with a big cavate: "How much of perfect focus can we see on the view finder of our digital camera? as any degree of out of focus, will show up in final image".

Then the next biggie is not infinity focus, if it is achievable. The main problem is that it can not be achieved, especially with certain brands (s.a. Canon) and on DSLR. This is due to "Flange distance" and mirrorless did really served us fine here.

Well I won't go over the details but if anyone has a question, please say so and I'll try to help, if I can. BTW if anyone interested to buy this type of lens, I can pass you some secrets and some good suggestions.

Yes mirrorless has helped a huge amount. My Celestron telescope cant focus to infinity with a DSLR in prime focus mode. With a mirrorless its easy :) I've never tried my DSLR on my Helios 1000mm scope just went straight to mirrorless. Despite the need for re-colimating the scope it works reasonably well with the tube tucked under my arm! I picked it up very cheap due to a dented tube, which has off-course got things out of alignment, so the two sides of the image focus at slightly different distances.