If you are talking the legacy CZ lens...
I have 5D mark 1 before (now upgraded to mk2). I have been playing a few cz lens as well, so maybe can offer you some help.
Recent acquired by
Jing Photography, on Flickr
I have got CZ planar 1.4/50, distagon 2.8/28, distagon 1.4/35, planar 2/100
First of all, you need an adapter ring.
Not all adapter ring the same. Some are very difficult to get off lens with sharp edge - particular those high polished stainlessness steel ones.
Some adapter ring comes with in focus confirmation chip.
This is handy - to know in focus on dim view finder takes good practices, I will come to this next. But there are other solution.
And certain adapter doesn't work - as far as I know, a chipped version doesn't go with planar 1.4/80.
Compatible issue, all above lens except d2.8/28 works fine with 5D. d2.8/28 can hit the mirror, you need to filter the element down.
Manual focusing, you need to wide open the lens, focusing and set back to correct focusing to take the shoot.
Use chipped version can take away this pain, but not all chipped adapter work, it is a hit and miss IMO since there are so many unbranded ones on the bay.
Alternatively, you can swap the focus screen to split image type. I opt for this approach. It works for me.
Light metering will not work since the camera do not know what f-stop the lens is on.
Which one?
IMO, 1.4/35 is the best ever lens for street and social documentary. You can always set to 5.6 and guess the distance to do hip shoot.
then 2/100 is a very good portrait lens for models can sit still.