Neutral density filters--do I have this right?

Discussion in 'Medium Format Cameras and Accessories' started by Jeffrey A. Steinberg, Apr 21, 2005.

  1. Jeffrey A. Steinberg

    Jeffrey A. Steinberg Member

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    I am new to medium format (about 2 years) after being a 35mm shooter. I want to make sure I have this right:

    When I want "out of foucs" backgrounds I usually use F4 and I like the effect. It requires high shutter speed if its really bright.

    In the same brightness, I am stuck at f22 or f16 due to the 1/500th speed of my Mamiya 7 or 1/400 (I think that's what it is) with my Mamiya RZ.

    If I get a neutral density filter of a particular type, it will block some of the light and thus allow me to work with a larger aperature/slower shutter speed combination such that I can get closer to F4.

    Is this correct? What do all you medium format shooters use for bright sunshine in the summer (i.e. what type of ND filter).

    I ask this because sometimes shooting in the morning or afternoon when there is less light is not possible and I have to shoot in very bright conditions.

    Thanks.

    Oh, and this is my 100th post. Boy do the first hundred go by quickly.
     
  2. smieglitz

    smieglitz Subscriber

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    Jeffrey,

    Each 0.30 of neutral density blocks one stop of light. To get from f/16 to f/4 you would need a -4 stop neutral density value of 1.20 units. For f/22 to f/4, a total of 1.50 units would be needed for -5 stops. The filters can be purchased in different increments to reach the exact values needed. They can also be stacked so if you had a -3 stop filter (0.90) you could add a -1 stop filter (0.30) to come up with a total of - 4 stops (1.20). Depending on the type of filter you purchase (glass vs gelatin, etc.,) you may find the filter density designated in either stops (e.g., -2 stop filter) or in neutral density units (e.g., 0.60 nd) or both.

    Each stop (0.30) of neutral density will require an exposure adjustment of 2x which is the "filter factor". You can either change the shutter speed by that factor or open the lens by the stop value. For example say you have metered an exposure without the filter to be 1/8 second @ f/5.6. You can either give 2/8 (=1/4) second @ f/5.6 or use 1/8 second @ f/4 with the filter in place. If the factor was 8x for a -3 stop filter using the same example, the new exposure would be 8/8 (=1) second @ f/5.6 or 1/8 second @ f/2 (or equivalent) with the filter in place.

    Joe
     
  3. bobfowler

    bobfowler Subscriber

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    I'll just tack on to Joe's response here...

    Use slower speed films when possible before resorting to a lot of N.D. filters. Sure, filters will cut the light levels down, but you'll be looking through a very dark finder on that RZ if you have to use -4 stops of N.D.! :smile:
     
  4. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    You've got it. If you are using a slow film and high shutter speed and still can't get the wide aperture you want, then ND filters are the solution. It's nice to have a set of three or four of them spaced one stop apart for different lighting conditions and effects. You can combine them, but that adds additional surfaces that can attract flare. If you like to do some long exposure effects, you can get an 8 or 10 stop ND filter for that purpose as well.
     
  5. Jeffrey A. Steinberg

    Jeffrey A. Steinberg Member

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    Thanks guys. Just wanted to make sure my understand was correct.

    Funny, I didn't think about slower film. I really like Tri-X so I tend to think about that only. I have not really used Plus-X. To most people here, does it have the "Tri-X" look or is it a different animal?
     
  6. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    It's different, but not a bad film. For a medium speed film, you might think more along the lines of Efke PL100 or FP4+. You could also shoot Tri-X with a developer that will give you a lower speed, like Microdol-X, which will give you fine grain, or ABC Pyro, which is grainy, but nice even in 6x7.
     
  7. Woolliscroft

    Woolliscroft Member

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    Just to add that the slightly longer lenses used in medium format tend to give a bit less depth of field anyway so you might not need to open up quite as much as you did with 35mm.

    David.