darr
Well-known member
I understand Doug, and I agree with the math and the reasoning behind it.By most traditional definitions, the entirety of the image frame needs to be covered by the lens image circle. Therefore (as noted by others above), the IC for 6x6 frames is, like any other format, the diagonal of the frame. Anywhere from 54x54 to 56x56 are reasonable ways of representing that frame (depends on which film back, which generation, and where along the not-a-completely-hard-line edge of the frame you consider the image to start.
That means only a lens with very roughly 80mm image circle or larger will fully cover 6x6.
Of course not every lens maker uses the same definition for their image circle size. Rodenstock, for example, tends to be very conservative and the illuminate (and in many cases, still reasonably sharp) area of the image projected is often larger than the number in their marketing material. In contrast Schneider tended to be very "optimistic" and in many cases the area that was sharp was smaller than the number in their marketing materials. Finally, "cover" is relative. There is nothing written on tablets from the sky that says you cannot use a lens that doesn't fully illuminate the rectangle (in this case a square rectangle) of your frame. Arguably the Holga lens didn't really cover the Holga format but that didn't stop people from creatively expressing themselves using that lens/camera combo.
So, basically, you have to put the lens on and see if you like the results. But if the image circle is notably smaller than 80mm, expect that the corners will be dark, black, or soft.
Sometimes though, a pro photographer needs to find a practical solution that will save money, time and get the job done. As an example, back in the film days many portrait photographers wanted the corners of their portraits burned in. Not only was this an elegant touch, but it helped to make your work rise above a non pro. Manufacturers were happy to assist, marketing various types of vignette systems to hang off lenses to create burned-in corners. Why do this someone may ask? Because the only way a pro could make money was to be behind the camera and not in the darkroom burning-in corners. We were taping our negatives to aperture cards and sending them off to a pro lab that made inexpensive machine prints, so your corners had to be burned-in on the negative.
I will bet there was a few crazy photographers that went looking for a solution that did not involve hanging more junk off an already heavy camera setup.
Nerdy artists tend to become photographers, just say'in.
Kind regards,
Darr