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  1. #1

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    film speed rating question

    Hello, I have what might be a dumb question, but I'd like to understand what happens on the development side when people rate a film at something other than box speed. If you rate Delta 100 at 50 because you want more shadow detail does this mean you also develop it for less time than if you exposed it rated at 100? This would reduce the dynamic range (contrast) of the image, right?

    Thanks in advance!

  2. #2
    polyglot's Avatar
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    Changing development time mostly affects contrast and it also has a small effect on speed. So if you want the same contrast with more shadow detail, keep the development time the same - you're basically saying "I care more about the darker parts of the scene than the lighter".

    Alternatively, you could reduce the development time with the additional exposure, which would allow you to fit a wider scene dynamic range - "I care about these shadows now, but also don't want to lose the highlights" - into the narrow DR of the print. It will look flatter though.

    A better alternative (IMHO) is to go for the extra exposure if necessary, keep your contrast up and then use printing techniques like dodging and burning to get the global dynamic range under control. That retains local contrast everywhere, hopefully without blowing out or blocking up sections of your print. It presumes of course that there are distinct areas of your image that can be dodged and burnt and that they're not horribly intertwined.

    If you want to be ultra-funky, you can make a contrast mask when printing. It's like a high-resolution custom dodge/burn tool made of film and it can save your butt if there are intertwined sections of the neg with wildly differing exposures. Split-grade printing can also be valuable, e.g. print one part of the neg at one grade and another part at a slightly different grade. Hard to make it look right though.

    Because the film has bit of a shoulder, burning down a sky may not work as well as you'd like - enough burning can prevent it blowing out, but the contrast might be poor because the sky was exposed past the film's shoulder. If there is a big brightness difference between two areas, a graduated ND is an excellent tool to use because it keeps the scene within the film's dynamic range (no toe/shoulder effects) and should mean less work when printing. And less grain from over-exposed areas.

  3. #3

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    Most people rate a film at less than box speed either because experience has shown them that the manufacturer's recommended film speed does not give them the shadow detail they desire, or because they've done a film speed test, and determined that, for their equipment and way of working, a speed lower than box speed is required.

    Generally speaking, if the manufacturer's recommended speed is too high, their recommended development time is usually too long, so most people who rate a film at lower than box speed also wind up developing their film for less time than recommended.

    Once you've determined the proper exposure index for a particular film, a simple test will show you what the proper development time is.
    "What drives man to create is the compulsion to, just once in his life, comprehend and record the pure, unadorned, unvarnished truth. Not some of it; all of it."

    - Fred Picker

  4. #4

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    When you take ISO 100 film and shoot it at ISO 50 setting, you are over exposing the film by one stop. When you develop this film, you cut the development time by 20% or so, so that you don't end up with super dense negative. At least that's the popular method.

    When you develop a film, a thin area gets developed to completion first. Then the darker area develops. Half way through the developing time, thin areas are fully developed and doesn't get much darker even if you develop it for looooong time. However, the darker area keeps going. So the given film with given exposure can have variety of contrast range depending on development time.

    When I'm faced with a VERY contrasty lighting, it is a common practice to over-expose and under-develop, to control the contrast on film. If I just want shadow detail but normal contrast, I am likely to develop normally or cut it by just a little. I might end up with darker negative but that only mean I have to expose longer when printing.

    Personally, I change the development time to control the contrast. If I wanted more shadow detail, I expose it differently but not necessary change the development time.
    Develop, stop, fix.... wait.... where's my film?

  5. #5

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    Quote Originally Posted by seadrive View Post
    Once you've determined the proper exposure index for a particular film, a simple test will show you what the proper development time is.
    What is the "simple test"? To shoot several rolls of the same scene with the same exposure settings and vary the development time, or is there a less costly way?

  6. #6
    David Allen's Avatar
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    The key to achieving consistently good negatives is the correct placement of your shadows when exposing the film and ascertaining the correct development time for achieving good separation without losing the highlights. A simple and relatively quick way to way to pin all this down for the future is to do the following (WARNING: reading these instructions is more time consuming and la more laborious than actually doing it!!):

    1. Find a scene with with a good range of tones
    2. Using the box speed, meter the darkest area in which you wish to retain shadow detail
    3. Move the camera so that you are only photographing this shadow area
    4. From the meter's reading close down the aperture by 2 stops or increase the shutter speed by two stops and then expose 6 frames at: the given exposure then +1 stop, +2 stops, -1 stop, -2 stops and -3 stops less than the meter has indicated

    5. Process the film

    6. Using the frame that was exposed at -3 stops less than the meter indicated (which should be practically clear but will have received lens flair and fogging - i.e a real world maximum black rather than an exposed piece of film that has processing fog) and do a test strip to find out what is the minimum exposure to achieve maximum black - Print must be fully dry before assessing this
    7. Do another test strip with the first exposure being what you have selected for achieving maximum black minus your dry-down compensation then plus 1 second, 2 seconds, etc
    8. The time that achieves full black inclusive of compensation for dry-down is you minimum exposure to achieve maximum black for all future printing sessions - print must be fully dry before assessing
    9 You now know the minimum time to achieve full black inclusive of exposure reduction to accommodate dry-down
    10. Using this minimum exposure to achieve maximum black exposure time, expose all of the other test frames.
    11. The test print that has good shadow detail indicates which exposure will render good shadow detail and achieve maximum black and provides you with your personal EI for the tested film/developer combination

    12 If the negative exposed at the meter reading gives good shadows, your EI is (when metering shadows where you wish to retain good detail) the box speed (i.e. for 400 film you need to set your meter at 400)
    13. If the negative exposed at +1 stop more than the meter reading gives good shadows, your EI is (when metering shadows where you wish to retain good detail) 1/2 the box speed (i.e. for 400 film you need to set your meter at 200)
    14. If the negative exposed at +2 stops more than the meter reading gives good shadows, you EI is (when metering shadows where you wish to retain good detail) 1/4 box speed (i.e. for 400 film you need to set your meter at 100)
    15. If the negative exposed at -1 stop less than the meter reading gives good shadows, you EI is (when metering shadows where you wish to retain good detail) double the box speed (i.e. for 400 film you need to set your meter at 800)
    16. If the negative exposed at -2 stop less than the meter reading gives good shadows, you EI is (when metering shadows where you wish to retain good detail) 4x the box speed (i.e. for 400 film you need to set your meter at 1600)

    You have now fixed your personal EI but there is one more testing stage to go.

    1. Find a scene with with a good range of tones
    2. Using your EI, meter the brightest area in which you wish to retain highlight detail
    3. Move the camera so that you are only photographing this highlight area
    4. From the meter's reading open up the aperture by 3 stops or decrease the shutter speed by three stops
    5. Expose the whole roll at this setting
    6. In the darkroom, process one third of the film for recommended development time

    7. When dry put negative in the enlarger and make a three section test strip exposing for half the minimum black time established earlier, for the established minimum black time and for double the minimum black time.
    8. Process print and dry it.
    9. If the section of the test strip exposed for 1/2 the minimum black time gives bright highlights with a trace of detail then the film requires 20% more development
    10. If the section of the test strip exposed for the minimum black time gives bright highlights with a trace of detail then the film is correctly developed
    11. If the section of the test strip exposed for double the minimum black time gives bright highlights with a trace of detail then the film requires 20% less development
    12. You can use the rest of the exposed highlight test film to fine tune the development time.

    YES - it is VERY boring but . . .for the investment of minimal materials and a few of hours you will have pinned down so many variables that it is really worth doing.

    Back in the real world, all you need to do in future is meter the shadows that you wish to retain good detail with meter set at your EI and then stop down the aperture 2 stops or increase the shutter speed by 2 stops. In the darkroom start your first test print with the minimum exposure to achieve maximum black (inclusive of dry-down compensation) and go from there.

    Best,

    David
    www.dsallen.de

  7. #7

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    I've done this....

    Set up a scene. Include objects that is black with texture, white with texture, 18% test card, and variety of other objects. Shoot a 36 exposure film at rated speed, in this sequence. At rated speed, one stop higher, and one stop lower. Remember to change your setting after every shutter click. Cut the film in 3 parts. Develop each film strip in standard length of time, +20% and -20%. You'll end up with 9 frames with variety of combination of exposure and dev time.

    Now, print all these 9 frames so that 18% gray in the scene is identical and at the right density.

    Place all those images on a matrix and examine for details in white and black.

    Doing this is easy but time consuming. Differences are also subtle. It shows how flexible and tolerant B&W films really are....

    As a result of my own test, I stop worrying about the "right speed" or "personal Exposure Index". I just shoot at rated speed unless I encounter extreme conditions.
    Develop, stop, fix.... wait.... where's my film?

  8. #8
    Bertil's Avatar
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    Less costly: cut pieces from the roll (perhaps enough to expose half of the roll, not hard with 35mm) and vary the development of these pieces.
    /Bertil

  9. #9

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    okay thanks everyone. I looked at the Delta 100 spec sheet from Ilford and it gives a shorter developing time if you have exposed the film at 50 - is this intended to be the time for pull processing or is it intended to be the time for normal contrast at EI 50?

  10. #10

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    If the time specified for EI50 is shorter than EI100, by definition, it's a PULL processing.
    Develop, stop, fix.... wait.... where's my film?

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