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Dali
03-02-2013, 07:10 PM
I would stay away especially from "old" lenses. I am not sure that the mirror coating lasts for decades... not to mention alignment issues and possible astigmatism due to mirror stress.

ME Super
03-02-2013, 07:46 PM
I have a Promaster 500mm cat lens that I bought new back in the mid-90s. It has come in handy a couple times for shots for which a 28-200 isn't long enough. My main issue with these is that they are tricky for ME to focus, because I don't see as well as I used to, and the DOF of a 500mm lens at f/8 is quite thin. When properly focused, they can do a decent job. When it's the difference between getting the shot or not getting the shot, this lens is adequate for the job.

AgX
03-02-2013, 07:50 PM
I would stay away especially from "old" lenses. I am not sure that the mirror coating lasts for decades... not to mention alignment issues and possible astigmatism due to mirror stress.

What is the difference between mirror stress and lens stress?

cowanw
03-02-2013, 11:15 PM
Mirror stress is reversed side to side.:)

Dali
03-03-2013, 10:13 AM
A mirror is thicker than a lens and is more prone to thermal expension/contraction. Being mounted thght in its cell, a mirror will show deformation it is can expend freely.

AgX
03-03-2013, 12:15 PM
A mirror is not neccessarily thikker than a lens, and to my understanding the mass of the element would be decisive.
(By the way: in a catadioptric lens a mirror and a lens can be formed by one single element.)

pentaxpete
05-05-2013, 03:01 PM
can I add something ? Many years ago now I got a RUSSIAN MTO 500 f8 mirror lens to use for Sport photos, mainly Cricket, for my local newspaper ( which went BROKE in 1980) and it was all B&W film work - I got some good results, many published photos -- it fitted my Screw-thread PENTAXes , ZENITHS, PRAKTICAS, and with a 'P' adaptor my CANON FTBn .
A ZENITH 'E' showing the wooden box it came with also one of the filters -- it cost me 69-00 from 'Brocks Cameras' ( now gone BROKE!)
http://farm5.staticflickr.com/4040/4328357708_bc95b3c04e_o.jpg (http://www.flickr.com/photos/25850987@N03/4328357708/)
Mirror Lens (http://www.flickr.com/photos/25850987@N03/4328357708/) by pentaxpete (http://www.flickr.com/people/25850987@N03/), on Flickr
'Walking on Water' taken with it , PRAKTICA MTL3, expired 'Activa' ( KONICA) 200 film rated 100 ASA
http://farm8.staticflickr.com/7012/6472166427_d72be49e3d_z.jpg (http://www.flickr.com/photos/25850987@N03/6472166427/)
Walking on Water ! (http://www.flickr.com/photos/25850987@N03/6472166427/) by pentaxpete (http://www.flickr.com/people/25850987@N03/), on Flickr
'Doughnut' Rings -- rear car light out of focus, PRAKTICA LB, expired Fuji Press 800 film
http://farm8.staticflickr.com/7010/6563314653_cd535f25b9_z.jpg (http://www.flickr.com/photos/25850987@N03/6563314653/)
Test 02: Russian MTO 500mm (http://www.flickr.com/photos/25850987@N03/6563314653/) by pentaxpete (http://www.flickr.com/people/25850987@N03/), on Flickr