Samyang 800mm f/8 mirror lens real life tests
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Recently I purchased this lens, could not resist. According to the results of nearly two weeks of working with it, I think, this lens has more flaws than merits. However, there are situations where it is irreplaceable and fared well. (I used it with Canon 5D mark II)

Positive aspects:
Bokeh, 800mm + f/8, lightweight, small, cheap, focus ring mooves very smoothly with no backlash, so focusing is possible (though perhaps it depends on the particular sample).
Negative technical aspects:
There are no that sharpness to which I was accustomed with Canon’s L lenses. I should artfully sharp images. And it’s not so much a bad image sharpness as the presence of a scattering around with more or less sharp details. Probably coma or some other aberration.
Shooting at shutter speeds longer than about 1/1000 on the tripod can only be done with mirror locking ON, otherwise – vertical shift. But shooting from hands could be done well with 1/200.
The main disadvantage of this lens when shooting people – the inability to communicate with the model on the working distances . Mobile phone does not work, because it is a long time to dial and it is very distracting. The solution may be in awalkie-talkie with a good speakers.
The complexity of the focusing I would put to second place in the shortcomings when photographing people.
Here I have already given frame showing good sharpness that you can achieve with this lens in the “home” environment.
Now field tests: All frames were made from a tripod with a long focusing using Live view mode and locking mirror option ON:
( Thanks Masha for her patience )
Do not pay attention to the focal length and aperture in the EXIF, I don’t have reprogrammed this adapter yet
on this picture I manually focused at night and, most interesting, well-focused:
and these are those excellent bokeh for which all this was started:
2sec, ISO100, Using a tripod, focused in Live view on horses on top, shooting from the museum near the guns. Click to see the 100% crop:
1/250sec, ISO400, using a tripod, focused in Live view. Click to see the 100% crop:
(vertical chromatic aberration – is because of the intense smoke which was here at this time)
Here is the the entire construction: