Originally posted by robtcorl I dug out a
Sigma MF 400mm f5.6 that I bought about 5 years ago, mainly to use on the original Q with adapter.
I've actually just been putting together a review of that lens. I think it's better than indicated in the reviews but it does seem prone to fringing - see test crop below, PF against white shirt. I'm not too surprised the images with the Q don't look that great, 5x crop factor scrutiny just shows up any flaws. Very decently sharp however on apsc (test pics with an NX20, 20MPx mirrorless).
And of the tame robins, F5.6 top, f9 below, cropped and resized.
And a blackbird with my K5, f11.
I definitely get better results with my FD 400mm f4.5, or my tamron 300mm f2.8, +/- tc. But this lens has a good spec inc PKA mount and a convenience cachet, a compact enough 400mm to easily fit in the lens pockets of
my camera bag.