Filters behind the lens...

[Lawrence Francis]

I seem to recall somewhere that using filters on the rear element of a large format lens produces some undesired result. Any one have any expeirence using filters mounted behind the lens? Whats the good/bad of this approach? Certainly filter cost would be reduced. Think about the cost of a front filter for Schneiders 210XL @ 135mm vrs a 72mm rear filter. Thanks for your help.

[Bruce Watson]

IIRC, a filter on the rear element of a lens will move your focus point by about 1/3 the thickness of the filter itself. I've lost some shots that way -- just slightly out of focus. All you have to do is redo your fine focus after the filter is in place. Also, if you put a filter behind the lens, it should be very clean. Other than that, it works as expected, for me anyway.

[John Cook]

In all the years I worked in commercial studios it was S.O.P. to put Wratten gels on the back of the view camera lens for color correction. Everybody did it that way. And only that way.

In my Hollywood days assisting in films, the cinematographers used to cut up square gels into small round disks and tape them to the back of their Arriflex cine lenses.

A smaller filter was required. It was less prone to dirt and flare. Better all around.

[neil poulsen]

One can adjust for the focus shift by focusing with the filter in place.

For wide-angle lenses, it can introduce a slight abberation. The more oblique the light path (from axis), the more filter through which the light must travel to reach the negative. So, the focus shift varies on the negative, depending upon how far it is away from the negative's center. This is true for any lens, but more pronounced for wide-angles.

With all this, I used gel filters and worried about it only when I was under a 90mm lens. But, I don't really know at what point it becomes a problem.

There can be an advantage. Filters mounted behind the lens can reduce flare, when compared with being mounted in front of the lens.

[lee\c]

I agree with Mr Cook. I have never seen any bad effect when putting a gel filter behind the lens. I suppose in theory the bad stuff could happen but that said, I can't see any problems with placing the filter behind the lens.

leec

[Paul Moshay]

In my studio I always use gels behind the lens and focus with them in place. Doing so keeps them clean and free from any flare even though I always use a large lens shade on the Toyos. The gels are so thin that focus shift would be unseen in any image. Paul

[David Vickery]

Gel filters are the best type to use on the back of the lens. They are almost optically pure, that is, they have almost no effect on the paths of the light rays going through the filter. This is why the previous posters report no ill effect with use on the back of the lens. This is also why companies like Kodak have made gel filters--they have almost no effect on the ray paths. They really only block color, or frequencies of the light going through them.

[j.e.simmons]

I use the thick, old, glass Kodak filters behind my barrel lenses. No problems if I focus with the filter in place