Originally posted by emiliano I'm considering the option of buying a focusing screen as well (about that: is it easy to install?).
It's not difficult, but it is time-consuming, since you have to calibrate it to your camera with shims to achieve correct focus.
I couldn't find one that showed shim installation. If you don't have a good pair of focusing screen tweezers like the ones in the video, you can pop the latch with a dental pick and use the plastic-tipped tweezers that come with most focusing screens. Regular tweezers will scratch the screen, so make sure you use plastic ones.
I've done it many times & while it's relatively easy, you'll no doubt need to change the shims to get correct focusing. That involves installing the screen, taking a test shot with a fast lens wide open to check for back or front focusing, removing the screen, changing the shim, replacing the screen, taking another test shot, etc etc etc... until it's right.
Here's a thread you might find helpful.
Just be careful, work in a clean environment, and wear latex gloves while you're handling the screen & you should be ok.
Good luck,
Bob :-)