About filters

[macandal]

Can someone tell me why is it recommended that filters be used in the back of the lens and not the front? I know this is a matter of preference, but I've seen it in different places where it is recommended that they are used in the back and not the front. Thanks. (Sorry, don't know enough about filters. Trying to learn more.)

[vinny]

Haven't heard that. I put mine in front since that's where the filter threads are
Hard to adjust a grad or pola behind the lens too. In fact, impossible.

[Bob Salomon]

Because some people feel that the loss in image quality by putting a filter behind the lens is not as important to them as the cost of the larger sized filter that is usually needed in front of the lens.

The only time a filter should be placed in any position other then the front of the lens is when the filteritself is part of the optical formula of the lens.
For instance, the Rodenstock HR Digaron-S lenses require a special glass plate be screwed into the back of the lens when the lens is used with film. When it is used with Digital that glass plate has to be removed. Anonther example are long Canon and Nikon lenses that accept drop-in filters.

[Drew Wiley]

Once in awhile the front element of a lens is so big that someone doesn't have a filter big enough for it, or can't afford a set that size. But with most typical view
camera lenses, putting a filter behind the rear element is going to compromise something, especially sharpness. Just for fun I did a little experimenting once to
confirm this, and did it with high-quality multi-coated glass filters. The ill effect was pretty obvious.

[Jerry Bodine]

Once in awhile the front element of a lens is so big that someone doesn't have a filter big enough for it, or can't afford a set that size. But with most typical view
camera lenses, putting a filter behind the rear element is going to compromise something, especially sharpness. Just for fun I did a little experimenting once to
confirm this, and did it with high-quality multi-coated glass filters. The ill effect was pretty obvious.

IIRC, anytime a filter is placed behind the lens it should be a gel filter to minimize the quality loss. In fact the Sinar Copal shutter has a clip on the back side to hold the gel in place, as shown here.

[Leigh]

Can someone tell me why is it recommended that filters be used in the back of the lens and not the front?

I've only seen that recommended (or even possible) by the manufacturers in two situations:
1) The front element is so large that a front filter would be very expensive, so they support a cheaper/smaller rear filter.
2) The angle of view is so wide that even a large front filter would vignette the image.

Most lenses don't have threads for rear filters.

- Leigh

[macandal]

Most lenses don't have threads for rear filters.

- Leigh

This is true for my lenses. Only one of them has threads in the rear.

[Drew Wiley]

Jerry - I think that recommendation of gel filters goes back to the early Pleistocene somewhere, prior to either high quality plano-parallel coated glass filters or humans learning to make fire to cook food. Gel filters are just about the worst option for sharpness today in my opinion (with the exception of thin cheap polyester substitute gels, or old-style heat-sandwiched Tiffens, which were basically gels cemented between glass).

[Jerry Bodine]

Jerry - I think that recommendation of gel filters goes back to the early Pleistocene somewhere, prior to either high quality plano-parallel coated glass filters or humans learning to make fire to cook food. Gel filters are just about the worst option for sharpness today in my opinion (with the exception of thin cheap polyester substitute gels, or old-style heat-sandwiched Tiffens, which were basically gels cemented between glass).

Drew, I appreciate your humor, but why do you suppose the folks at Sinar don't seem to think there's a problem with either gels or their Color Control glass filters or a combination of the two being used behind the lens? Or maybe I should ask them?

[Bob Salomon]

Drew, I appreciate your humor, but why do you suppose the folks at Sinar don't seem to think there's a problem with either gels or their Color Control glass filters or a combination of the two being used behind the lens? Or maybe I should ask them?

Anything behind the lens will shift the focus by about 1/3rd the thickness of the thing behind the lens. A common use of this was Hasselblad's inclusion of a glass plate in their Polaroid film holder that shifted the focus when Polaroid was shot so the image plane of Polaroid matved their roll film backs.

In Sinar's case they were not placing a thick glass filter behind their shutter but only a very thin gel filter. The image shift from a thin gel is negligible compared to the shift from a glass filter behind the lens. Especially in those old days when even thin glass filters were non readily available.