Filters on wide FOV lenses

[Ed Richards]

Been doing some tests on vignetting with filters on my 47mm XL (FOV 120 degrees) and 80mm SS (FOV 105 degrees). This should also apply to my 110mm XL, but on 4x5 it is pretty unusual to get to the edge of its image circle.)

I use the center filter and the Lee adapter for this on the 47. This works fine, but it is a bit of a pain. I tried using an 86mm filter on the center filter, and had significant vignetting. Back to the Lee. Since polarizers are not a good idea on ultra wides, I only need to use one contrast filter on the 47.

I had been using a 67-72 step up ring on the 80, but noticed vignetting in several pictures with significant rise. (You should not put filters directly on the XL lenses, there is no enough clearance with the front class.) I put the lens on the Sinar so I could get more rise than the Ebony, and did some testing. First, I think this lens has a larger image circle at F16 than the manufacturer lists. I raised it to where I was sure I was out of image circle, but found I was still not vignetting without a filter. Using the 72, I got significant vignetting. Less with a 77mm filter, and none with the recommended 67mm Extra Wide, which has a filter diameter of 82mm. (Bought one of these to try, took 6 weeks to get, and when I ordered a second one, I found they are discontinued except in MRC coating, and not yet available in that.) The 67mm EW should be the same as using a Heliopan 67-82 step up ring (they make the only brass rings and the others tend to bind) and a B+W or Heliopan filter.

I then tried the Lee adapter ring for wide lenses, and it alone added a very little vignetting. This might have been due to the Lee polarizer ring I have on the holder. No additional with a filter. Adding the polarizer lead to very significant vignetting.

I do not have a square polarizer to try to with the Lee holder, but it should be less of a problem than the round one. There should also be less problem with light getting in between the polarizer and the filter. But I do not use a polarizer much, so I may just decide to stick with one I have to save money. The square would be a problem with grad filters, but I never seem to use those either.

I then tried a 67-86 step up ring and B+W filter on the 80. Got some vignetting. The only adapter ring in that size I could find was a crappy Century ring, which was thick and so badly made that it would not screw all the way into the lens and the filter would not screw all the way into it. In 86mm, the B+W filter is also very thick, so between the two problems I can see how would be worse than the 82. Adding an 86-105 ring and the Lee polarizer only made things worse.

Bottom line - You need extra wide filters to get the least vignetting with the 80 and similiar lenses. The Lee system is close enough to be acceptable. You have to use a Lee type system to use filters on the 47 if you use the center filter.

[Leigh]

B+W makes slim filters specifically for this application.

- Leigh

[Ed Richards]

Have now tried the B+W wide filter (82mm front) with a thin polarizer. Lots of vignetting.

But I am beginning to wonder about the lens coverage. The 80mm XL should have excess coverage of 34mm rise on portrait orientation. I pushed my Sinar with the bag bellows up higher than this, and yet I still did not see any vignetting without a filter at f22. Is the estimated lens circle for this lens very conservative?

[Leigh]

Ed,

The specified image circle (IC) gives you the lens coverage with no degradation.

Degradation can take many forms besides vignetting.

I would accept the manufacturer's specs if you want nominal lens performance.
If you can accept degraded performance, then certainly use your own tests and decide what's right for you.

Regarding filters...
Filters for wide-angle lenses are meant to be used singly, not stacked. This is true of the slim filters particularly.
Many WA lenses have provisions for rear-mounted filters, which are smaller, cheaper, and less prone to vignetting.

The Apo-Symmar-L section of the latest Schneider catalog in my file contains the following statement:

"The Apo-Symmar L, like other Schneider lenses, has an additional filter thread
on the mount of the rear lens (see the table on page 25)."

Unfortunately my copy has no page 25.

- Leigh

[aporodagon]

If you can get hold of a Hasselblad Polarizing filter labelled 93 mm (a wide angle design with 86 mm threads used for the 40 mm and 250 mm lenses) it will attach directly to the 80xl centre filter. It also has the advantage of being able to be rotated from behind.

[Bob Salomon]

"Many WA lenses have provisions for rear-mounted filters, which are smaller, cheaper, and less prone to vignetting."
But will degrade the image unless the lens was designed for rear filters.

[Leigh]

But will degrade the image unless the lens was designed for rear filters.

Bob,

Please read my post #4 above where I quote the Schneider datasheet.that says their lenses
"have a filter thread on the mount of the rear lens".

A lens with a filter thread on the rear is "designed for rear filters".

If it has no rear thread, it's not designed for rear filters,
but the argument is moot since there's no way you could mount one in the first place.

- Leigh

[Bob Salomon]

Leigh,

A place to mount filters on the rear is one thing. That is the thread that usually holds the rear trim or even the glass in.
A lens designed to take rear filters usually has filters made by the lens manufacturer specifically for that purpose. Not just a thread for any screw-in filter.

But to each their own in any case. Just remember, once the light rays have passed through that lens the lens has done what it was designed to do. Now adding something to the glass is also going to do things to those light rays, lack of parallalism in the filter, dust, scratches, smudges, fingerprints will all negatively impact the quality of the image.

Also, that information about the rear threads in their lens brochure states page 25 but the drawing is on page 23 and the sizes are on page 24 even though the L pages states page 25. Page 25 is the displacements info.

[Leigh]

Hi Bob,

Not necessarily true.

None of my sixteen Nikon, Rodenstock, and Fujinon lenses has rear filter threads,
not even the 65mm Nikkor which would be the most likely candidate for a rear filter.

- Leigh

[Nathan Potter]

Bob, I have been under the impression that when filter threads are available on the rear outside element on LF lenses then those lenses are sold with the correct filter blank. The lens has been designed for a specific glass thickness and index so that on axis and off axis rays converge at the focal point equally. Any other filter one buys needs the same thickness and index to achieve maximum resolution - except a near infinitely thin supplementary filter like a thin plastic. Maybe I'm misinformed?

Nate Potter, Austin TX.