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Thread: 90mm for 6x17

  1. #11

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    I would say that a 120 APO-Symmar would have more light fall off compared to a 120 Super Angulon. The Super Angulon is a wide angle design that has less fall off.

  2. #12
    David A. Goldfarb's Avatar
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    With any 90mm lens on 6x17, you're probably going to want to correct the falloff to some extent, either on the lens or in the darkroom, particularly if you shoot color transparency film. If you shoot B&W and don't mind lots of falloff, maybe it won't matter as much, but if you correct it to some extent, it gives you more compositional flexibility. More falloff tends to drive the subject to the center of the frame, or stated alternately, when the subject appears in the falloff zone, you may just find that image to be unsuccessful when you look at the contact sheets or transparencies, because these things can be hard to judge on the groundglass.

    Even with a center filter--even the filter supposedly "matched" to the lens--the correction isn't 100%, but might be visually acceptable. If center filters actually corrected falloff fully, which they could only do at a specified focus distance and aperture, they would usually be around three stops and would presume a shooting aperture of around f:22. At one point, such filters were made, and they didn't sell particularly well, because they were impractical, so most of the available center filters tend to correct about 1.25-2 stops at f:22 and leave an aesthetically acceptable amount of falloff. Heliopan may still have a 3-stop center filter. I have several wide lenses, and I haven't had any particular problems like banding with "unmatched" center filters, and I haven't found it necessary to purchase "matched" center filters with only slight differences in density.
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  3. #13

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    I have one of those 3-stop CFs, made by Schneider and marked 8/90mm. It doesn't appear in the literature in their online archive, but they recently sent me a scan of a 1967 document that lists it. The document is slightly wrong as it says exposure time should be extended 3x while the filter measures 3 stops, but it has the correct physical dimensions. The front threads are 82mm, unlike the later IIIa and IIIb which are 86mm. It also lists filters for the 65mm and 75mm Super Angulons.

    Send me an email if you want a copy of this 1.9Meg PDF.

  4. #14
    jbbooks's Avatar
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    Quote Originally Posted by ChuckP View Post
    I would say that a 120 APO-Symmar would have more light fall off compared to a 120 Super Angulon. The Super Angulon is a wide angle design that has less fall off.
    Let’s see—if you go to the following link, you will find an information chart for Schneider lenses. The chart lists eleven different centerfilters made by Schneider for use with their Super-Angulons, older Super-Angulons and for their Super-Symmar Aspheric lenses. There are no centerfilters recommended for use with their APO-Symmar lenses.

    https://www.schneideroptics.com/pdfs...LensCharts.pdf

    So, according to your logic, Schneider does not recommend centerfilters for those lenses that really need a centerfilter, but does recommend them for those lenses that do not need them so much.

  5. #15
    SMBooth's Avatar
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    I actually decided to get a Fujinon 105 f8 because of the 250mm IC until a Nikon 90mf8 came my way at a very reasonable price. Going to hold of of the CF until I get camera finished and some shots from it.
    Thanks for all the help

  6. #16
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    Quote Originally Posted by SMBooth View Post
    I would I be right in saying that just because a faster lens has a greater image circle, the vignetting or edge falloff start around the same distanse from the centre of the lens, or does a F4.5 with a 235mm IC show less fall off on a 6x17 image then a f8 with 216mm IC because the IC is bigger and the falloff is further out.
    Lenses have a natural cos^3 or cos^4 falloff with respect to angle and because a given film size subtends a greater angle with a shorter focal length, there will be more falloff than with a longer focal length. Different lens designs lead to different amounts of this natural falloff.

    It's got nothing to do with coverage, which is generally where mechanical vignetting kicks in and gives you a distinct image circle. And likewise, a faster lens does not necessarily have greater coverage at all - tele lenses (where the rear nodal point is well forward of the rear of the lens) generally have less coverage than you might expect from their focal length.

  7. #17
    David A. Goldfarb's Avatar
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    Quote Originally Posted by Steve Goldstein View Post
    I have one of those 3-stop CFs, made by Schneider and marked 8/90mm. It doesn't appear in the literature in their online archive, but they recently sent me a scan of a 1967 document that lists it. The document is slightly wrong as it says exposure time should be extended 3x while the filter measures 3 stops, but it has the correct physical dimensions. The front threads are 82mm, unlike the later IIIa and IIIb which are 86mm. It also lists filters for the 65mm and 75mm Super Angulons.

    Send me an email if you want a copy of this 1.9Meg PDF.
    I have a Schneider center filter from that era for my 65/8 Super-Angulon, and like yours, it's marked with the name of the lens, but it actually measures about 1.5 stops, so 3X rather than three stops. Thanks for the offer of the document. I'll send you an e-mail.
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  8. #18

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    Quote Originally Posted by jbbooks View Post
    Let’s see—if you go to the following link, you will find an information chart for Schneider lenses. The chart lists eleven different centerfilters made by Schneider for use with their Super-Angulons, older Super-Angulons and for their Super-Symmar Aspheric lenses. There are no centerfilters recommended for use with their APO-Symmar lenses.

    https://www.schneideroptics.com/pdfs...LensCharts.pdf

    So, according to your logic, Schneider does not recommend centerfilters for those lenses that really need a centerfilter, but does recommend them for those lenses that do not need them so much.
    Well a lens like the Symmar drops off at cos^4 and the Super Angulon drops off at cos^3. So I would say that a 120mm Super Angulon would have less fall off at any angle off the center line. Center filters aren't used on Symmars because they don't have the kind of wide angle coverage that would need them. They only cover 72-75 degrees compared to the 100 or so for the Super Angulon.

  9. #19
    Ole
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    On the other hand, a plain old Angulon would need a center filter more than a Super Angulon would, even if both are wide angle lenses.

    Cos^4 is the falloff expected from a simple symmetrical lens with no "fancy tricks" - a perfect pinhole would give cos^4 fall-off. By using a large strong negative element to "tilt the pupil", also known as Biogon-type (even if the Biogon wasn't the first), the fall-off will approach cos^3. Most lenses come nowhere close to this ideal, and the difference really only gets significant when you get around 45 degrees off the lens axis - meaning about 90 degrees coverage. The wider the angle, the larger the difference. At 100 deg angle of view, a cos^3 lens loses about two stops, a cos^4 lens almost three.
    -- Ole Tjugen, Luddite Elitist
    Norway

  10. #20
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    Quote Originally Posted by ChuckP View Post
    Well a lens like the Symmar drops off at cos^4 and the Super Angulon drops off at cos^3. So I would say that a 120mm Super Angulon would have less fall off at any angle off the center line. Center filters aren't used on Symmars because they don't have the kind of wide angle coverage that would need them. They only cover 72-75 degrees compared to the 100 or so for the Super Angulon.
    What I posted was based on what the OP said in a prior post, which led me to believe that the camera that he was intending to use the lens in is one which will not allow movements:

    What he wrote, in part, was, "This is a DIY 6x17, so at the point to pick a lens before finishing off the nose cone..."

    The point I attempted to make was that I thought the OP ought to consider a longer focal length than 90mm for his fixed lens, non-movement camera. When I tried that format, I found that the 120mm focal length was much more useful than the 90mm. We can agree, I hope, that is a subjective conclusion and there is no basis, other than individual preference, for his choice of focal length for his camera. I simply suggested he ought to consider another.

    If I am correct in that the OP's camera will not have movements, there is no need for him to use a lens that has an image circle larger than 179mm, the approximate diagonal of the 6x17 format. A 120mm f5.6 APO-Symmar has an image circle large enough to cover that and using a larger, heavier, perhaps slower and more expensive lens that needs a centerfilter, such as a 120mm f8 Super-Angulon, is not necessary.

    If I am wrong about the coverage of an APO-Symmar or about the intended use of the lens in a camera that does not have movements, then I stand to be corrected. On the other hand, if I am correct about the coverage of the APO-Symmar and that no capability for movements will be available in the OP's camera, then there is no reason for any concern about the fall off in exposure for the APO-Symmar as opposed to the fall off in a Super-Angulon. For its smaller angle of view, the fall off in the APO-Symmar is negligible and, as you recognize in your post, above, it does not need a centerfilter.

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