SMC Pentax - M 50mm f2

[Jim Schemel]

My brother has a very nice copy of the above mentioned lens.Just wondering if it is a solid performer and if it can be used on a 5D with infinity focus? Do they need to be converted or can you buy an adpater?
-Jim

[aoleg]

While I cannot comment on the performance of this particular lens, the K-mount lenses are a hassle with the 5D. Yes, there are K-EOS adapters available, plenty of them on eBay. They allow for infinity focusing. However, they should only be used on crop bodies because Pentax lenses have aperture stop-down levers and corresponding protective flanges that will hit the mirror of your 5D. In order to use the lens with the 5D, you will need to remove the flange (by unscrewing the three small screws holding the black inner part; this one is easy to do) and sometimes (not always) by also removing (or filing down) the aperture stop-down lever.

Now, whether or not the rear glass of the lens will hot the mirror of the 5D even after those things are removed is another story. It probably will, but I haven't tried this lens.

All in all, it's better to use this lens on a crop body where it'll make for an excellent, super-fast portrait lens.

[Jim Schemel]

aoleg,
thanks for the quick reply.Are you able to tell me how your Pentax 50mm f2 performs?
-Jim

[aoleg]

I only used it on a crop camera, Canon 40D. I don't risk mounting it on a full-frame 5D, and I am reluctant to remove the aperture stop-down lever.

It's nice and sharp even wide open, with smooth rendering (but 6-bladed diaphragm). Images looks similar to Nikkor 50/18, with maybe a bit smoother rendering (that's subjective). Contrast is very decent. For the money, you cannot go wrong with this lens. It sells for around $35-45 depending on the condition.