Why do we need center filters?

[Dan Fromm]

But the manufacturers aren't trying to achieve perfect correction anyway, just to mitigate the most severe effects, so there's wiggle room.

Ah, yes, Heliopan.

[Oren Grad]

Ah, yes, Heliopan.

From Schneider's current CF sheet:

"To avoid too long exposure times and with consideration of the exposure latitude of the film emulsions, the vignetting of the lenses has not been fully compensated."

[David A. Goldfarb]

From Schneider's current CF sheet:

"To avoid too long exposure times and with consideration of the exposure latitude of the film emulsions, the vignetting of the lenses has not been fully compensated."

And this is why I don't really believe in the idea that center filters should really be though of as dedicated to specific lenses, apart from questions of physical size. Some of these are just 1/4 stop or 1/2 stop apart at the center. I was once shooting with a friend who had a Schneider IIIb, and I tested it against a Schneider III that I use with a few different lenses, and even comparing the transparencies side-by-side, you would be very hard pressed to tell which was the "correct" filter for which lens, because they don't correct fully. Some people seem concerned about the hypothetical possibility of exposure banding due to mismatched curves, but I have yet to see anyone produce an actual example of this. It's more of an aesthetic choice that you could only decide upon based on experience.

So personally, I have two center filters--one is dedicated to the 65/8 Super-Angulon, and it doesn't fit any other wide lenses that I have (49mm thread), and the other is a Schneider III (1.25 stops), and I use it on wide lenses that take 67mm filters (47mm SAXL, 55mm Apo-Grandagon, 75mm Apo-Grandagon, 90mm SA). If I start using the 47mm more often, maybe I'll consider the recommended 2-stop IIIc for it or a 3-stop Heliopan, more likely the latter, but meanwhile, it's not as if I can't use what I have.

[Oren Grad]

And this is why I don't really believe in the idea that center filters should really be though of as dedicated to specific lenses, apart from questions of physical size. Some of these are just 1/4 stop or 1/2 stop apart at the center. I was once shooting with a friend who had a Schneider IIIb, and I tested it against a Schneider III that I use with a few different lenses, and even comparing the transparencies side-by-side, you would be very hard pressed to tell which was the "correct" filter for which lens, because they don't correct fully. Some people seem concerned about the hypothetical possibility of exposure banding due to mismatched curves, but I have yet to see anyone produce an actual example of this. It's more of an aesthetic choice that you could only decide upon based on experience.

So personally, I have two center filters--one is dedicated to the 65/8 Super-Angulon, and it doesn't fit any other wide lenses that I have (49mm thread), and the other is a Schneider III (1.25 stops), and I use it on wide lenses that take 67mm filters (47mm SAXL, 55mm Apo-Grandagon, 75mm Apo-Grandagon, 90mm SA). If I start using the 47mm more often, maybe I'll consider the recommended 2-stop IIIc for it or a 3-stop Heliopan, more likely the latter, but meanwhile, it's not as if I can't use what I have.

In the same vein, I contacted Schneider recently to ask about the difference between the IIId and the IV, which are both 82mm, for use with a 120 SA. The representative who responded answered very sensibly - he mentioned the difference in gradient and its role in achieving a better match to the falloff characteristics of specific lenses, but added that he understood that budget can be an important consideration, and that it's perfectly reasonable to try the cheaper one (in this case, IIId) to see if the effect is sufficient for one's purposes.