If the old lenses are manual type, how does thius affect camera auto focus, metering etc. Can i actually use manual lenses on a Digital Camera. It really depends on what brand of lenses and camera that you are using. For example, Nikon has never changed their lens mount and old manual lenses can go on any SLR camera that they make. They won't affect the camera, but you can't use the auto focus feature, you have to switch it over to manual focus, as they lack the "motor" to focus them. As far as metering, the camera should still function completley normally for that. I use my old a/f lens on my new digital SLR
the focal length will change by 1.4 on average
as for manual lens? I can only relate my own experiences.
I used to own a Canon EOS50 with a couple of Canon zoom lenses.
When I bought a Canon digital SLR I found that though the lenses of the old camera would fit they would not automatically adjust the focusing and aperture.
I ended up having to buy lenses suitable for my new camera.
It may be a marketing ploy by Canon to make you replace your lenses and this may not be typical of other brands.
Your best bet would be to take your lenses to a camera dealer and try them out on the camera that you would like to purchase. It depends on the brand, most nikon models can accept their manual lenses but you may have to perform stop down metering.
Pentax can accept any k-mount lens, the level of communication will depend on whether its a k, ka or kaf.
Canon will accept any EF lens but wont accept lenses from the F1, AE-1 T90 etc (FDBL & FD mount) With the Nikon D200, D2Xs,D2Hs can use the spot and center weight meter with a Modified AI, AI, AIs, and E series Manual focus lens. NO Best compatibility is the Pentax K10D/K100D/K110D cameras
Any AF lens has full functionality
Any manual focus "A" series also has full funtionality (except autofocus)
Any "M" or "K" series manual focus lens will still meter via step sown metering and can use Aperture priority settings
Any "S" aka screw mount lenses can meter via step downmetering but you neet a $22 adapter to mount the lenses.
Nikon has second best compatibility
D40/D40x/D50/D80 can mount old MF lenses but will not meter. D200/D2xs can accept and meter from AI and AI-s series, older Non-AI's will not meter.
Canon/Sony will not accept older manual focus lenses
Olympus can accept the old OM lenses with a $100 adapter | 