DHu said:
Should I just go ahead and get the 75/2.5 Heliar?
I didn't realize there are limitations to the Bessa R2 body on using a faster lens. Would you mind explaining why it won't work? I was going to either wait for a new CV 75mm/90mm or look for a used Leica. Thanks for the pointers.
All of the recent Bessa bodies use a 37mm rangefinder base line. The viewfinder magnifies the 2 images that are being brought to coincide by the rangefinder as the lens is focused. On the Bessa R/R2/R2A, the magnification is 68% of life size. The R3a magnifies the images to 100%, or full life size.
The combination of the length of the base line & the degree of magnification determine the precision that can be achieved in focusing any lens. Because of the shallow depth of field that results from a longer lens, greater precision is required to achieve accurate focus. Because wider apertures also result in shallow depth of field, the combination of the two (long focal length + wide aperture) compounds the problem even further, requiring even more precision in the focusing mechanism.
Cosina clearly felt that lenses of 75/2.5 & 90/3.5 could safely be focused on the pre-R3A Bessa cameras with reasonable accuracy. Since they haven't offered any lenses faster than these at these focal lengths, they don't seem to be as confident of the camera's focusing accuracy beyond these limits. However, with the introduction of the R3A, it would appear that new possibilities are now available. Cosina has offered no hints of anything in the works so far, but it would seem to be a natural development to accompany the increased capability of the R3A.
If you have the Bessa R2, then you'd probably be best advised to go for the 75/2.5 Heliar as the safe choice. A used Leica or other used M-mount lens in the 75-90 mm focal length - such as Konica, Rollei, etc. - remain an option. They would just require greater care in focusing at apertures wider than those that Cosina offers, especially when used at the lens's minimum focus distance. But at all other apertures, they can be used just as easily & confidently as Cosina's own Voigtlander lenses.
If you want further technical explanation of the whys & wherefores of the limits of frangefinder focusing, you can refer to either of these links:
www.cameraquest.com/leica.htm
www.imx.nl/photosite/leica/technics/rfaccuracy.html