Camera: Canon 5D Mk2
Lens: Helios 50mm 77M-4
Video recording format: default H264
Lens setting: @f/2
Test subject: bokeh
It's hard to perfectly deliver untouched file due to compression features of YouTube, still i hope this will give you a general feeling of how this lens is. Is test is a bokeh test and is meant to show how lens performs with close focus setting - showing you properties of out-of-focus area of picture.
Is is one of many Helios branded lenses with focal range of a standard lens - 50mm (technically some models are 52mm, some are 58mm but you got the point). Cheapest and most popular 50mm Helios lens is 44M (an all of its models from 2-6, and while we are on a model descriptions, 77M-4 seems to be much more popular than 77M but they all are pretty similar so don't get hanged up on model numbers), 77M is a different animal. Being a tiny bit faster that 44M (f2 vs f1.8), somewhat rare and much more expensive. Now is there a point of buying one instead of 44M? Image quality wise probably not, my general feeling is that 77M is a bit sharper lens up to f2.8 and down from there i cant see much difference. Still, if you have extra money to spend it's a highly recommended lens for good reasons. I had an opportunity to get one and didn't pass on it. As a student and hopefully future pro, i simply like the best i can afford.
Why have this lens at all? Bokeh. This lens (and other Russian lenses too, like 44M and Mir 1B) produce a very specific bokeh with circular distortion (or swirly bokeh or some other term i am not aware of). When used right way it gives you a nice barrel effect that is very lookalike to old cinema lenses and somewhat reminds me of an anamorphic effect. I personally love it to bits. This video shows you how bokeh gets oval towards the frame edges.
Who is this lens for? Full-frame camera users are the most lucky ones (smaller sensors will simply miss the edge of a frame so that the whole bokeh swirl effect is less evident). APS-C sensor size is still ok, but smaller ones are not in luck and i don't recommend it to be used on those. It's a great lens for photo and video work, manual focus is always a hustle so nothing is changed here.
Computability is always a question with adapted lenses. On Canon 550d (t2i) and EOS 3000 i had no problems. On Canon 5D Mk2, when focused to infinity (or close to infinity) rear element of lens goes too deep into body and makes contact with mirror. Now with video that's not a problem, but taking photos is a bit difficult... as you understand, mirror hitting lens is not a welcome feature.
My final verdict is - Helios 77M-4 is a highly recommended lens, if it's features are something you looking for.
p.s. here is a photo sample that explains the whole bokeh thing too