I would like to purchase a zeiss or leica 35 mm to be used with a canon 40D? Has anyone had this combo and be willing to give me suggestions?
When I read the the shooter must use stop down metering with a manual focus lens does that mean that I actually will lose f stops and cannot use the lens in as low of a light situation on the canon?
In reading about the 35mm lenses I most often see that the quality of Canon's L and a zeiss or leica are similar? Why is the canon a much heavier lens?,
Stop down metering simply means you need to close the aperture to the value that you want for light metering (and the actual shot). Of course you can shoot with a fully open aperture, so no, you don't lose any stops. The canon lens has an electric aperture and electronics to tell the camera what the full aperture of the lens is; metering is then done with fully open aperture and the camera calculates the needed exposure for any smaller aperture. The aperture doesn't close until you release the shutter. The Leica lens doesn't have the electronics and no electric aperture, so you need to stop down the aperture manually.
The Leica 35mm Summicron R (latest 3 cam version) would be an excellent lens for a 40D. It is sharper than any Zeiss in the centre, in my experience, and that includes the ZF 35, so there's your 40D frame. It is not as sharp in the corners on a 5D, but that doesn't matter at all on a 40D. It also has a built in hood, which is useful.
But are you an experienced manual focuser? It takes quite some time to get teh hang of, especially on a camera body with an average viewfinder like the 40D.
Only the Contax/Yashica (C/Y rather than Contax G) lenses can be used on a 40D. You should have no problems with any Contax/Yashica mount lens, but the Contax G mount lenses are not compatible. I'd go Leica regardless for a 40D.
If you want a manual focus lens, make sure to get the Ef-S focusing screen for your 40D. It makes manually focusing very easy.
I think you mean Biogon by Bogen, and no you can't use Biogons on a DSLR. Biogons are designed for rangefinders (or G-series cameras) and Distagons are for SLRs.
The EF-S screen also makes the metering work correctly. You have to set a special function to tell the camera which focusing screen is installed. With the standard screen, you will get exposure errors that vary with aperture. Many folks just live with this, but I found it a royal pain. The EF-S is much better.
