Centre filters for UWA lens - rear element instead of front

[lenicolas]

Thank you for the correction. English isn’t my first language. ^.^

[Rod Klukas]

One other item. The lens is designed to direct the light to the image plane/film/digital back in a certain trajectory. Years ago some photographers would use gel filters on the back of the lens. These were so thin that a single filter would cause negligible image issues. But a glass filter perhaps 2-3 mm thick, and with flat, supposedly top and bottom surfaces will bend the light differently than the lens designer intended.
And as Bob solomon correctly noted the image is focused 1/3 the thickness of the filter differently. That is why you never focus and then add a filter to the front of a lens for a sharp image, by the way.
So although some of these lenses do have threads, I would be checking before I just slapped a Center filter on it. Also the Angle with which the lens projects the image to the film plane is different than the angle of acceptance of the front of a lens. So to be truly maintaining your image quality you would really need a center filter tuned to that particular lens. Expensive and so small customer count, as someone noted above.
I can say that lenses which have matched center filters should have them if at all possible. I have tested many of the combinations and the increase in quality is quite noticeable.
Hope this is informative.
Rod

[Alan Klein]

One other item. The lens is designed to direct the light to the image plane/film/digital back in a certain trajectory. Years ago some photographers would use gel filters on the back of the lens. These were so thin that a single filter would cause negligible image issues. But a glass filter perhaps 2-3 mm thick, and with flat, supposedly top and bottom surfaces will bend the light differently than the lens designer intended.
And as Bob solomon correctly noted the image is focused 1/3 the thickness of the filter differently. That is why you never focus and then add a filter to the front of a lens for a sharp image, by the way.
So although some of these lenses do have threads, I would be checking before I just slapped a Center filter on it. Also the Angle with which the lens projects the image to the film plane is different than the angle of acceptance of the front of a lens. So to be truly maintaining your image quality you would really need a center filter tuned to that particular lens. Expensive and so small customer count, as someone noted above.
I can say that lenses which have matched center filters should have them if at all possible. I have tested many of the combinations and the increase in quality is quite noticeable.
Hope this is informative.
Rod

I've never considered that. I'm new to 4x5 view cameras. I've added polarizers and contrast filters to the front but after focusing. So focus changes when I do this? Do center filters have to be added before final focus as well?

How do you see through the lens with filters. Doesn't it make too dark?

Finally, I'm using a Schneider center filter on a 90mm Nikkor lens that is suggested for this lens. Nikkor has no center filters for their lenses of their own. So what does that mean? How does that effect my procedures?
Thanks.

[minh0204]

I've never considered that. I'm new to 4x5 view cameras. I've added polarizers and contrast filters to the front but after focusing. So focus changes when I do this? Do center filters have to be added before final focus as well?

I think Rod made a typo, he meant one should not add a filter to the rear of the lens after focusing.

This is the same issue as putting a Fresnel lens between the ground glass and the lens, it will shift the focus.

[Drew Wiley]

Alan - Don't worry about that. I already did plenty of testing with the 90/4.5 + CF + contrast filters too. Just go ahead and focus first, then add the filters. But REAR mounting filters on a lens is a no no unless otherwise specified. There are some modern lenses which are less than ideally corrected, especially at the widest apertures, and can exhibit a bit of focus shift between different colors of very deep contrast filters, even high quality glass ones mounted on the front. So when in doubt, carefully test. It's more likely to be a problem with MF lenses.

[grat]

If you want a truly ridiculous question, why can't you take the equivalent of a "flat" image using lens "X" (ie, evenly lit diffuse exposure), which should show the falloff fairly well, load that image into software, invert it, and print it on a transparency?

You should now have a lens-specific center-spot ND "filter", and assuming it's the right size you should be able to put it in front of the lens.

I try to have at least one crazy thought a week, and figured I should get it out of the way early this week.

[Drew Wiley]

Grat - can be done. But you wouldn't have a truly hue-neutral gray if color shooting were involved. Reflections could also be an issue. And then there's the issue of light-scattering in those silver grains different than how official ND filters are made to specifically avoid that. But try it just for fun.

[Bob Salomon]

If you want a truly ridiculous question, why can't you take the equivalent of a "flat" image using lens "X" (ie, evenly lit diffuse exposure), which should show the falloff fairly well, load that image into software, invert it, and print it on a transparency?

You should now have a lens-specific center-spot ND "filter", and assuming it's the right size you should be able to put it in front of the lens.

I try to have at least one crazy thought a week, and figured I should get it out of the way early this week.

Fine, if you can put up with the less then neutral color and use it on a camera with no movements.

[Dan Fromm]

Finally, I'm using a Schneider center filter on a 90mm Nikkor lens that is suggested for this lens. Nikkor has no center filters for their lenses of their own. So what does that mean? How does that effect my procedures?
Thanks.

I wrote an article that addressed this. There's a link to it in the list. Read it. If you don't remember what the list is or where to find it, please ask.

[Alan Klein]

Alan - Don't worry about that. I already did plenty of testing with the 90/4.5 + CF + contrast filters too. Just go ahead and focus first, then add the filters. But REAR mounting filters on a lens is a no no unless otherwise specified. There are some modern lenses which are less than ideally corrected, especially at the widest apertures, and can exhibit a bit of focus shift between different colors of very deep contrast filters, even high quality glass ones mounted on the front. So when in doubt, carefully test. It's more likely to be a problem with MF lenses.

I shoot MF RB67 also. So, are you referring to filters on the front or the rear?