Effect of using filter on rear element?greenspun.com : LUSENET : Large format photography : One Thread
I have recently purchased a new Schneider 110mm XL lens. I am really nervous about leaving the glass exposed and am tempted to put filters on both the front and back. I plan to use high quality B+W filters. Firstly, will this degrade the image to a noticeable extent? I may want to stack another filter on the front, say a yellow or red. Will having three additional pieces of glass (albiet good ones) affect the image quality enough to worry me?
Secondly, does anyone know if the rear element has the same problem as the front element, in terms of the filter touching the glass? Also can anyone confirm that the rear element has a 52mm thread? - I am not confident to measure it myself.
Bob Salomon in another thread says that putting a filter on the back element causes focus shifts and image degradation if anything is on the filter. How big a problem is this? Would it be a problem with a high quality filter like B+W?
If anyone has tried this could they please let me know how it went?
Many thanks for your help!
-- Andrew Herrick (email@example.com), August 22, 2000
Whether you use the highest quality filter made (Heliopan) or another there will always be a focus shift = to 1/3rd the thickness of the filter plus a filter on the back is going to reduce performance more when it is on the rear since the lens has already processed the image. When on the front dust, dirt, fingerprints, smudges, etc. are far less likely to effect the image then ones on the back.
-- Bob Salomon (firstname.lastname@example.org), August 22, 2000.
Alas, I must cocur with the other posters. The rear filter will degrade the image. BUT I have seen many images made by an artist who always uses gelatin filters behind his images, and I can't see the degradation in 24x30s. Like you I just purchased a 110 XL. I find I can use Gels in a Kalt/Caulumet holder in front of the lens; I have also used glass behind; the glass of lens and filter do not touch in a rear mount position. So far I can't see any image degradation no matter where I mount the filters. I know it exists. And in some critical applications or if one is sloppy it could caause problems, but so far...
-- Bob Moulton (email@example.com), August 22, 2000.
Bob is correct, however, I'd like to add my 1/2 cents. Although I'm not a profession, I'm learning Architectural photography from one who does it for a living. He uses Color Correction and Light Balancing gel filters behind the lenses with excellent success. Even under a loupe, the transparencies show virtually no difference in quality. In keeping with Bob's statements;1) Focus with the filter in place. That should compensate for the focus shift. 2)Clean dirt, dust, fingerprints and smudges off of the filter as, hopefully, you have done with the rear lens element and maybe even the front. As Bob stated, contamination on the rear element will have greater degradation than that of the front. I would venture to guess that anyone desiring the ultimate in image quality isn't taking photographs with contamination on any of the elements including the filters. I realize the some location shooting may not have the best of conditions. Another benefit of having the filters behind the lens is that it is less likely get dust, dirt and fingerprints because it's inside the camera. Ultimately you will have to decide for yourself if the degradation is acceptable to you, so the best advice is to try it both ways and check the results. Regarding the lens (110 XL), extra, extra caution should be used mounting filters on the front, the lens actually sticks out quite a bit and the filter threads are shallow. A filter that also has shallow threads will touch glass-to-glass. I use a 67-82mm step-up ring for my polarizer, to avoid vignetting and glass-to-glass contact.(All other filters are behind the lens) And, yes the rear filter size is 52mm. Good luck, Gary.
-- Gary Jones (firstname.lastname@example.org), August 22, 2000.
Filters used on the rear are less likely to throw flare. (According to Schneider.) I like using gels on the rear, and focusing with the filter in place. I would discard a filter that was grimy, etc.
I have a reducing lensboard. I've mounted a 4" Xenophon filter holder (from Calumet) onto the back of this reducing lensboard in such a from way that it does not interfere with mounting the smaller lensboards. This simple device meets all my filter needs for color or black and white.
-- neil poulsen (email@example.com), August 23, 2000.
How bout just being careful?!? Three filters??? C'mom.
-- sheldon hambrick (firstname.lastname@example.org), August 23, 2000.
Three filters? NO. Waht are the other two, UV's to "Protect the lens? That is camera store baloney. Use a filter on the rear? By all means. If you want to use glass, focus through it. I have use gels taped to the rear of the lenses on my very large cameras for years. No degradation and no problems with focus shift. Jim
-- Jim Noel (email@example.com), August 29, 2000.