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Thread: Nd filters versus stopping down

  1. #1

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    Nd filters versus stopping down

    A question of curiosity only.

    Is there any advantage in using a ND filter rather than stopping down a lens, or vice versa?

    For instance using a ND8 filter on a f5.6 lens. Does that change the lens to the equivalent of a f11 lens, or does it merely allow a longer exposure without changing the optical properties of that f5.6 lens.

    I’m wondering, for example, of the depth of field of a f11 lens versus that of a f5.6 lens with ND8 filter attached. Assuming no structural differences in lens type etc.

    Also, for the sake of this query I’m ignoring the extra glass element between the subject and the recording media; which could affect the quality of the recorded image.

    Regards
    Tony

  2. #2

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    Re: Nd filters versus stopping down

    A ND filter does not change the DOF. It just cuts down the light getting to the film. So how much DOF you want needs to be determined first. At the same time, you need to determine what speed you want to shoot at. An ND will impact either of these -- or both.

    Instead of opening the lens to compensate, you can use a slower shutter speed and preserve the DOF.

    One problem is that different manufactures use different designations for their ND filters, for example ND4, 0.6ND, ND2X, etc. They do this just to muddy the waters.

  3. #3

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    Re: Nd filters versus stopping down

    Quote Originally Posted by xkaes View Post
    A ND filter does not change the DOF. It just cuts down the light getting to the film. So how much DOF you want needs to be determined first. At the same time, you need to determine what speed you want to shoot at. An ND will impact either of these -- or both.

    Instead of opening the lens to compensate, you can use a slower shutter speed and preserve the DOF.

    One problem is that different manufactures use different designations for their ND filters, for example ND4, 0.6ND, ND2X, etc. They do this just to muddy the waters.
    No they don’t. 0.3 is 1 stop of density. 0.6 is 2 stops, 0.9 is 3 stops.
    Some companies mark their filters in density values.
    Others mark them in the filter factor. 2x.

  4. #4

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Bob Salomon View Post
    No they don’t. 0.3 is 1 stop of density. 0.6 is 2 stops, 0.9 is 3 stops.
    Some companies mark their filters in density values.
    Others mark them in the filter factor. 2x.
    Exactly my point -- it confuses many shutterbugs.

  5. #5

    Re: Nd filters versus stopping down

    If it confuses folks then they can simply carry conversion charts or mark each filter in whichever way they find non-confusing.

  6. #6
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    Re: Nd filters versus stopping down

    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.

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    Re: Nd filters versus stopping down

    Quote Originally Posted by consummate_fritterer View Post
    If it confuses folks then they can simply carry conversion charts or mark each filter in whichever way they find non-confusing.
    Exactly my point -- it confuses folks.

  8. #8

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    Re: Nd filters versus stopping down

    Quote Originally Posted by xkaes View Post
    Exactly my point -- it confuses folks.
    Then those folks should learn proper terminology for their hobby. Lots of books explain it in simple language. So do many brochures from filter manufacturers, not private label filter suppliers, except for Hoya. I was Product Manager and Sales Manager for B+W and then Heliopan and I still find Hoya brochures confusing!
    And that is also after many years as a photographer and a graduate of the USAF photo school!

  9. #9

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    Re: Nd filters versus stopping down

    Apologies for presenting a small format example.

    Tony, I used to shoot flowers, insects and such at magnifications from 1:6 to 0.88:1 with my Nikon FM2n. Kodachrome 25, 1/250 shutter speed, flash illumination, typical effective aperture f/22 or f/32. Live unconstrained fish in small aquariums, too, same settings. All of the exposure came from flash, none from ambient. That's what I wanted and that's what forced shooting at such small apertures.

    The results were marginal for publication, couldn't be printed as large as I'd have liked because of loss of sharpness to diffraction.

    I stopped doing all this when Kodachrome processing went away. The apertures needed to let me overpower ambient with ISO 100 film were far too small.

    I still have Ektachrome in the freezer and Fuji is still selling 35mm color reversal film so I've been thinking about shooting flowers again. It may be time for me to get a 3- or 4-stop ND filter or two. I find the idea of such dense filters repugnant, but its the only way to overpower ambient with flash and shot at reasonably large effective apertures.

  10. #10

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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

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