I have a couple older white lenses that have the drop in door. As long as you have the filter tray in there isn't really any further use or need for it or them. That was a hold over from film days where you did need a UV to correct the blue spectrum. That is unnecessary with digital. and any further filter needs can be done in Photoshop and probably it is best to do it there. Make sure you're using raw, however.
EB
EOS 1DX and 1D Mk IV and less lenses then before!
