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Thread: Nd filters versus stopping down

  1. #11

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Jim Jones View Post
    Tony, using a ND filter doesn't change the optical performance of the lens. Instead, it permits (or demands) longer exposure time. Some photographers find this useful in photographing star trails, moving water, or eliminating pedestrians in urban landscapes. It may be better than stopping a lens down so far that diffraction limits image sharpness.
    This is an important factor, I'd add next:

    Here we have lens optical performance measured (Line pairs per mm) by practical (not lab) gear, depending on aperture: http://www.hevanet.com/cperez/testing.html

    Here we have a table showing sharpness limitation depending on aperture, at f/64 no lens can deliver more than 25 Lime pairs per mm resolution: http://www.kenrockwell.com/tech/diffraction.htm


    Another factor is fall off with short focals, for example a 65mm lens in 4x5 will have an insane amount of fall off in the corners at f/5.6 and using ND4, while it can be well reduced to around 2 stops at f/11 with no filter

  2. #12
    Jac@stafford.net's Avatar
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    Re: Nd filters versus stopping down

    I appreciate the scientific optics presented because I like science,
    but do large format photographers really care about diffraction?

    For those who do care, just how large do you print and what is
    your anticipated viewing distance?

    Many thanks.

  3. #13

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Jac@stafford.net View Post
    I appreciate the scientific optics presented because I like science,
    but do large format photographers really care about diffraction?

    For those who do care, just how large do you print and what is
    your anticipated viewing distance?

    Many thanks.
    Well, 4x5 lenses are typically diffraction limited by f/22. If we stop beyond that we can save money in the lens, by f/32 diffraction limits resolution of a $3000 glass to what a 1960 Symmar does (coatings apart). If we stop to f/45 we are limited to 35 lp/mm and we are in the same league than Pre WW II gear...

    Does it matter ? it depends... not for Sally Mann, she can take also a great image even with the bottom of a coke bottle.

    But if we put big money in glass because it is 80 Lp/mm capable but we usually end stopping at f/32, then it matters.

    (This is iMHO)

  4. #14

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Jac@stafford.net View Post
    I appreciate the scientific optics presented because I like science,
    but do large format photographers really care about diffraction?

    For those who do care, just how large do you print and what is
    your anticipated viewing distance?

    Many thanks.
    Jac, if you directed that question to me, 8x12 full frame prints from 35 mm KM slides (8x enlargement) were visibly soft at 18". 4-5x would have been fine but 8x was a bit over the limit.

    Whether the softness detracted from the final prints is an interesting question that I can't answer because it depends on the viewer's expectations. I didn't like it at all.

  5. #15

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    Re: Nd filters versus stopping down

    Use the ND if you want longer than normal exposures and/or shallow DOF...

    Steve K

  6. #16

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    Re: Nd filters versus stopping down

    Quote Originally Posted by LabRat View Post
    Use the ND if you want longer than normal exposures and/or shallow DOF...

    Steve K
    YOU NAILED IT.

    Just figure out how much ND you have or want.

  7. #17

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    Re: Nd filters versus stopping down

    One other factor to consider is color cast. Not all ND filters are truly neutral. The editor of On Landscape, an online landscape magazine published in Britain, looked at a handful and found significant color cast in some of them. As I recall, the resin filters were the worst, and one of the best was a glass ND filter from China. This may not be a big issue for B&W photographers, but for color film users is concerning.

  8. #18

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Bruce M. Herman View Post
    One other factor to consider is color cast. Not all ND filters are truly neutral. The editor of On Landscape, an online landscape magazine published in Britain, looked at a handful and found significant color cast in some of them. As I recall, the resin filters were the worst, and one of the best was a glass ND filter from China. This may not be a big issue for B&W photographers, but for color film users is concerning.
    Very true!!!

    It's like wearing sunglasses... We don't notice the color cast or shifts because our brains adapt, but what do you see on a lightbox or while printing/scanning???

    Steve K

  9. #19

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Jim Jones View Post
    Tony, using a ND filter doesn't change the optical performance of the lens. Instead, it permits (or demands) longer exposure time. Some photographers find this useful in photographing star trails, ...
    Interesting. I strongly suspect you're not speaking out of your experience. Could you kindly explain how a ND filter can be useful in photographing star trails?? Thanks in advance.

  10. #20
    Jim Jones's Avatar
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    Re: Nd filters versus stopping down

    Pfsor, star trail photographs often use exposures of many hours. Sky light can then wash out the faintest stars. Either stopping down or using a filter compensates for this. As I recall, a 11 hour polar area star trail on 35mm Kodak Tech Pan film in the Midwest worked best between f/5.6 and f/8 without a filter. I wouldn't have wanted to stop down smaller than f/8 due to diffraction.

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