I note that I can choose from three focussing screens for my 40D. there are often times when i would like to rely on manual focussing but I miss the split image and crossed microprisms I used to use. Will changing the focussing screen that came with the camera make manual focussing any easier? I realise that I cannot get the screens i would really like.
The three Canon focusing screens as I recall when I had a 40d are the one that came with the camera, a second with etched lines and one for low light shooters that use fast lenses. None for the 40d offer a split-prism as you found out. I will say you have to be very careful when changing screens so as to avoid dust. I did fine on my former 40d and a current 5DMk2 as I prefer the etched screens. I thank Canon for not having to do that on the 7D. I remember the first time I changed a screen on a Canon A-1 (about 1979) and got dust on the backside of the screen. Ended up I bought a second screen.
Canon don't make a screen for the 40D specifically designed for manual focusing. There are some 3rd party screens available though which do have focusing aids. An alternative manual focusing aid is to use an eyepiece magnifier or Live View. Using Live view with 10x magnification will give you very good feedback on focus, but of course it's a slow process and you can't do it with your eye to the viewfinder.
Thanks for that advice. I have used liveview and liveview with the camera connected to my computer which is very successful. I did not realise that there were third party screens available though.