Old FD mirror lens - new digital life?

It Is All Done With Mirrors, Mirror Lenses, That Is
What about mirror lenses? I can get a really cheap telephoto that way!

In the film days, I never got any keepers out of this lens because of its poor contrast.  But with Photoshop, there's some hope of adjusting levels to compensate.  This lens also can be focussed past infinity, so I was able to remove the glass optics from the adapter and still have it focus at infinity.

A tripod was used for all shots.  In each of the tests, the displayed image is the best of at least 3 snapshots.  Mirror Lock-up (MLU) and EV bracketing was used for the Sigma 600mm f/8 mirror lens.  For the AF lenses, refocussing was forced for each exposure.  ISO800 was used to give reasonable shutter speed for the mirror.  JPEGs are Baseline ("Standard") Quality 10.

Sigma 600mm f/8 mirror 600mm ISO800 1/250 -1EV full-frame down-sized

Sigma 600mm f/8 mirror 600mm ISO800 1/250 -1EV auto-levels, full-frame down-sized

The unprocessed image on the left shows the poor contrast of the lens.   On the right, Photoshop auto-levels has fixed the levels, and it certainly gives better results than I ever got out of a Besseler 45MXT, stock 50mm enlarger lens, and high-contrast paper.

How does the Sigma 600mm f/8 mirror compare with resizing images from better quality 200mm lenses?

Sigma 600mm f/8 mirror 600mm ISO800 1/250 f/8 -1EV auto-levels, full-frame down-sized

Canon 55-200mm f/4.5-5.6 USM II 200mm ISO800 1/640 f/10.0 full-frame down-sized

Canon 70-200mm f/2.8L IS USM 200mm ISO800 1/1250 f/7.1 full-frame downsized

The above shows the field of view, given the difference in the focal lengths of the lenses.

Sigma 600mm f/8 mirror 600mm ISO800 1/250 f/8 -1EV auto-levels, full-frame down-sized

Canon 55-200mm f/4.5-5.6 USM II 200mm ISO800 1/640 f/10.0 cropped, down-sized

Canon 70-200mm f/2.8L IS USM 200mm ISO800 1/1250 f/7.1 cropped down-sized

The above shows images cropped to a similar view, given the difference in focal length for the lenses.

Sigma 600mm f/8 mirror 600mm ISO800 1/250 f/8 -1EV detail full-crop, auto-levels

Canon 55-200mm f/4.5-5.6 USM II 200mm ISO800 1/640 f/10.0 200mm detail crop, up-sized, auto-levels

Canon 70-200mm f/2.8L IS USM 200mm ISO800 1/1250 f/7.1 detail crop, up-sized, auto-levels

The above shows center detail crops.  I didn't set up well for edge detail crops - sorry.

I took other tests shots, and should have used f/8 for all of the above.  But the above images are probably sufficient to answer the question.  It appears to me that the images from the 200mm zoom lenses have higher quality than the image from the 600mm mirror, even after correcting for contrast by levels processing.  I might as well shoot at 200mm and crop.  Sad to say, I'm better off leaving the dust on the mirror.

Maybe the current Sigma mirror is better.  But I'm not a poor student any more, and the advantages are mostly with the standard dioptric refracting lenses.  You have many more choices of shutter speed, aperture, and ISO.  There's less need for tripod and mirror lock-up, especially with the IS lens.

I've tried Adorama Canon FD Lens to EOS Body Adapter with the FD 50mm f/3.5 macro and FD 85mm f/1.8 lenses.  These lenses are sharp enough that the images are good even with the adapters optics.  How much I'll actually use them before they are replaced with AF lenses remains to be seen.

I had one bright spot with the Sigma 600mm mirror in the past.  With a 5X eyepiece, I used it as a telescope to look at Jupiter.  When I saw the Galilean moons with my own eyes for the first time, I was utterly amazed, especially seeing how the moons lined up in the ecliptic!  It made me wonder a lot about Galileo, his discoveries, and experiences.