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!)

Mirror Lens by pentaxpete, on Flickr
'Walking on Water' taken with it , PRAKTICA MTL3, expired 'Activa' ( KONICA) 200 film rated 100 ASA

Walking on Water ! by pentaxpete, on Flickr
'Doughnut' Rings -- rear car light out of focus, PRAKTICA LB, expired Fuji Press 800 film

Test 02: Russian MTO 500mm by pentaxpete, on Flickr