LOLOL, film cameras, DSLR's, Canon focusing screens

Manual lenses on DSLRs is not exactly a picnic. There's several reasons why

1...Most/ all? DSLR cameras have MUCH smaller viewfinders than did the old school 60's-70's SLR counterparts. In the case of my old Canon XT/350D less than 1/2 the size

2...In the case of Canon Rebel series, the vewfinder is not "fed" with a prism--it's a mirror, so you lose some light right there

3...The main mirror down in the shutterbox in a DSLR is PARTIALLY TRANSPARENT because of the metering / autofocus. So not all light gets up to the viewfinder to start with

4...In addition, I think we likely have a tendency to "make use of" the nice big resolution in modern cameras, where back in the day, we ended up with, and were "happy" with a much smaller print. So errors REALLY show up badly

5....You must set aperture by hand, it does not stop down automatically (except with some Pentax electrically driven apertures on old lenses) so trying to keep focus--on a moving subject--you are looking through the thing stopped down. That is, unless you have some high quality really fast glass

All these things add up against you. My "keeper rate" for anything except sunsets, etc with manual glass is quite dismal.