I've been making occasional visits to a nearby bog, both for the exercise and for photography. I wanted a lens with a bit more reach but preferably not too much bulk and not too expensive. With some doubts I decided to take a chance on an inexpensive 500 mm mirror lens. This morning I took it back to the bog to take some sample pictures, some of which I show below. The captions show my recollection of how far away but they are simply guesses, not measurements and not even the better estimates that with some forethought I could have read off of the lens.

The lens has a fixed aperture of f8 and that gives no control over depth of field (and bokea). The narrow depth of field should be apparent in all of the images below. Focus is pretty critical and is manual only.

With a fixed aperture my usual habit of shooting in aperture priority seemed to make no sense so I shot in shutter priority, but I left ISO as automatic so that the camera had a chance to make adjustments for low light; but the lighting was strong enough so that did not come into play. I'm not sure what would have happened if I'd use aperture priority, however. Perhaps that would be a better choice.

As if one experiment were not enough, I decided to try something else today at the same time. In the past I've used a monopod at the bog, thinking a tripod would slow me down too much. Animals just don't stay still long enough to set up a tripod. But I have a tripod that has one removable leg so you can build a monopod out of it. I've never used it for that, but it occurred to me that I could also take advantage of that to construct a bipod with more stability than would be possible with a monopod. It is also more bulky to carry around but I think the extra stability is worth it.

Wow! Thanks for the info and the link to your "labor of love." I learned much. And I greatly appreciated the effort and time investment you have given to capturing some of the history as well as valuable information. I will use it to look at the serial numbers of my Nikon lenses. Thank you, again.
This range of contributors and the information is part of what I treasure from participating on UHH.
I was in the photo industry - worked retail in independent camera stores and chain stores during HS/college, graduate from RIT (Rochester, NY), Southeast Region Purchasing Mgr. with Eastman Kodak stores (renamed Treck Photographic), the Product Manager with Charles Beseler (making darkroom hardware and importing chemistry from Germany for 'Color by Beseler' products), the Omega Division COO of Berkey Photo at 26, Rollei USA Marketing Mgr., Osawa, Hindaphoto, and a few more. Left in 1985 for the computer hardware/software solutions business after the experience of computerizing several of my photo manufacturing/distribution companies. (Info just for perspective)

And the very best of the catadioptric mirror lenses are usable with the high MP cameras of today - if the lens is still in proper alignment, has no 'balsam separation' between the optical lenses, no fungus growing and spreading across any of the lenses or between the elements and the mirror coating is still intact. Next, if the mirror lens has 'passed' the first test, does the focusing feel smooth and usable? Last (or first), does it have a mount that will fit onto your camera?

Recommend that you buy through a venue like ebay or something similar that allows you to receive the lens and test it on your equipment or return it if it is not satisfactory.

This should save you at least one 'bad' purchase on the way to finding a good to great lens for a bargain price! Happy Hunting.

Usable, but pics will be soft by comparison to other lenses. They are just getting left behind by technology...along with a LOT of other lenses.
Even the venerable Nikon 105 micro 2.8 cannot resolve past 36 MP. I don't think anyone would argue a catadioptric lens is sharper than the 105.
There is an entire list of Nikon lenses that cannot keep up with todays camera bodies. I talk about Nikon only because it's the only line I could find where testing was done. 27 lenses were tested...not old lenses either...10 failed (including the 105 micro).
If you have a 24mp camera...you're fine...for now.
But the tech of cameras and their respective lenses keeps moving at a very fast clip.
I have some fine Minolta glass that does great on my Sony A77M2...but I'm not even going to bother attaching them to my Sony A7RIV ... waste of time and effort.
So folks will either have to buy the newer lenses...which are incredibly sharp (they have to be)...or stay in the lower MP bracketed camera bodies...forever.