Center Filter Behind SA 72mm XL

[Todd Young]

Can anyone think of a good reason as to why a ND Grad filter could not be placed behind a Schneider 5.6/72mm SA XL?...The Schneider filter made for this lens; all but makes it impossible to use any other filtration, it;s cost notwithstanding.....Being fairly handy and having a machine shop; I have been considering the careful mounting of a 72-77mm step-up ring to this lens' rear element and using a 77mm Heliopan neutral density center gradient filter for the Fuji GX-617 90mm lens, which I already have.....Or: perhaps modifying a B+W 77mm UV filter; to fit onto the rear element, no only for the UV elimination benifit but also to avail myself of the ability to thread other filters to the rear.....Most of my shooting seems to include lots of sky and water scenes and I really need to be able to use my circular polarizer...(B+W KSM 95EW)....Thus: my quandary.....Any Idea's?

[Garry Teeple]

I would think that using a filter larger than the lens would place more of the dark center farther out to the edge of the lens where you don't want it. But like everything esle, try it and see.

[Michael S. Briggs]

If you use a thick filter behind a lens, you should focus with a filter in place. This is necesary because the filter material, having a different index of refraction than air, changes the optical distance from the lens to the film. The light loss caused by the filter might make focusing with it in place difficult.

A center filter has a particular radial density profile that is based upon the distance of the filter from the enterance (or in your plan, the exit) pupil. Since the manufacturers sometimes offer one center filter for several lenses, the density profile can't be too critical, nevertheless, using a different center filter at a different location may or may not give good results. The best way to find out is to try it. Before doing the work of machining an adapter, you could try a test photo with a center filter taped into place.

The other ways of using additional filters with the center filter are to spend the $$ for a 112 mm diameter filter to use in front of the center filter, or to use thin filters such as Lee polyester or gelatin behind the lens.

With LF cameras, since they don't have beam splitters for metering, there is no need for a polarizer that makes circular rather than linear polarized light, though the more expensive circlar polarizer will work.

[Eric Woodbury]

I use this lens with gel filters on the front. I have cut a circle in a square piece of foam core so that it just slides over the front outer diameter. I then have little paper corners taped to the foam core so that it will retain a 4" gel in a frame. Works great and cannot be seen in the image. Gels are so thin, focus shift is neglible.

This answer has nothing to do with the graduated center filter, but does make for a good filter holder for the front.

[Mark Davies]

Hi Todd, I have the 72saxl and an Ebony 45SU. I find just with the lens in, without any extra filters behind it there is minimal movement left. Putting a filter on the rear of the 72 will reduce even further any movement you may have.

But a good thought, I will be interested to hear your results.

Regards,

Mark