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Thread: PEI, Push-Pull, Exposure Confusion

  1. #1

    PEI, Push-Pull, Exposure Confusion

    I am new to LF but not new to film, but I still have questions about developing. With 35 mm developing with an in camera spot meter, I have become good and repeatable with my small tank development, but I never really went beyond developing film based on the normal spec sheet times/temp. 36 frames had way to many different frames with varying contrast.

    I expected to use LF sheets to learn about deviating from the spec so I can control contrast, but my progress at sheets even from the spec sheet (patterson tank or tray) has been problematic - sometimes perfectly exposed and more often underexposed/underdeveloped.

    But before I continue to try to debug my process, I think I first need to get my head around a few concepts. Can someone help me understand what the differences conceptually between the following and how they relate as well.

    1) Personal Exposure index
    2) Pushing and pulling from normal development
    3) Using film a particular film at a non-specified ISO like "TMAX 400 exposed at 200"
    4) Setting a given meter reading to be on Zone III instead of V

    All of these manifest themselves in one way or another to modifying the values from my spot meter.

    I believe my goal is to find my 1) so I know that I can correctly expose for my shadows by 4) so I can control the contrast with 2), but I don't know why anyone would do 3)?

    What don't I understand?

    Thanks,
    Andy

  2. #2

    Join Date
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    Re: PEI, Push-Pull, Exposure Confusion

    Contrast = development
    Density = exposure

    That's about it.

    -30-

  3. #3
    Octogenarian
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    Re: PEI, Push-Pull, Exposure Confusion

    If you haven't done so as yet, I suggest that you first read Ansel Adams. "The Negative".

    Then, read Steve Anchell and Bill Troop, "The Film Developing Cookbook".

    Those two books will answer most of the questions you have asked.

    With B&W film, you need to expose for the shadows and develop for the highlights.

  4. #4

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    Re: PEI, Push-Pull, Exposure Confusion

    Quote Originally Posted by mmmdoughnuts View Post

    But before I continue to try to debug my process, I think I first need to get my head around a few concepts. Can someone help me understand what the differences conceptually between the following and how they relate as well.

    1) Personal Exposure index
    2) Pushing and pulling from normal development
    3) Using film a particular film at a non-specified ISO like "TMAX 400 exposed at 200"
    4) Setting a given meter reading to be on Zone III instead of V

    All of these manifest themselves in one way or another to modifying the values from my spot meter.

    I believe my goal is to find my 1) so I know that I can correctly expose for my shadows by 4) so I can control the contrast with 2), but I don't know why anyone would do 3)?

    What don't I understand?

    Thanks,
    Andy

    Andy,

    A good bit of information on each of these areas can be found on this site via the search function - advanced search of subject title tends to yield better results IMO.

    Brief explanations -

    1 - Finding your personal exposure index, is essentially matching your film to your equipment - camera, lens, meter, developer, etc. - this is found through testing with a series of exposures, and looks at the low values of your negative (least affected by varying development times.) This is very much related to # 2 and #3.

    2 - This involves a few factors - First normal development must be found - The manufacturers 'Normal' may be different that what you will find normal, again matched to your camera, lens, meter, developer, film, etc. Longer and shorter deviations from normal effect upper values more-so than the low values. The common term - Expose for the shadows, Develop for the highlights - comes from this. After #1 is found, you can find your 'Normal Development' by adjusting development times.

    Expanding and Contracting development times relates to adjusting your development time to the metered scene - you can extend or reduce the range of contrast in a scene through changes in development.

    Pushing and pulling development is a bit different, and usually relates to purposely exposing a film at higher or lower ISO than your normal EI, and then compensating with longer or shorter times.

    3 - Once you test your film with your equipment, you may find that a 100 speed film rated at 100 doesn't give you the information in the negative you want. Adjusting this speed allows you to tailor the film speed to your equipment and process - many rate their film speed lower than rated - but again this is through testing.

    4 - Your meter reads 18% gray +- - it doesn't take into account the subject. Assuming you are using a spot meter - Metering a white wall and exposing at the indicated exposure at 'your' correct ISO will essentially record a gray wall on your negative, with normal printing - considered Zone V. Increasing exposure by two stops would record the white wall as Zone VII on your negative, and essentially print white, with normal printing. Same is true for Shadow detail - the meter will again show Zone V, and if exposed and printed normally will be Zone V in the resulting print. To place the shadow at Zone III, decrease the indicated exposure by two stops. The resulting negative when printed normally will be darker at Zone III.


    Hope this helps...

    Thanks,
    Dan
    Last edited by DanK; 17-Aug-2010 at 20:02. Reason: Spelling

  5. #5
    ic-racer's Avatar
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    Re: PEI, Push-Pull, Exposure Confusion

    Exposure and development are independent.
    Development time fits the negative to the paper, thats the only reason to fine tune the time.
    Adequate exposure is that which places the important scene values on the usable portion of the film curve.

  6. #6

    Re: PEI, Push-Pull, Exposure Confusion

    Quote Originally Posted by DanK View Post
    Andy,

    1 - Finding your personal exposure index, is essentially matching your film to your equipment - camera, lens, meter, developer, etc. - this is found through testing with a series of exposures, and looks at the low values of your negative (least affected by varying development times.) This is very much related to # 2 and #3.
    My two light meters are equivalent to about 1/3 of a stop. I have built a LED source and used an oscilloscope to time my shutters at each speed so I believe that I am (within 1/3 stop) dealing with just temperature and time now and I am starting to work with a step wedge to get the PEI right.


    I think this is exactly where my confusion is. Is 3) in reference to someone's PEI 1) or is someone pushing the film to get more grain and/or a different film curve for contrast 2))?
    Quote Originally Posted by DanK View Post

    2 - This involves a few factors - First normal development must be found - The manufacturers 'Normal' may be different that what you will find normal, again matched to your camera, lens, meter, developer, film, etc. Longer and shorter deviations from normal effect upper values more-so than the low values. The common term - Expose for the shadows, Develop for the highlights - comes from this. After #1 is found, you can find your 'Normal Development' by adjusting development times.



    Expanding and Contracting development times relates to adjusting your development time to the metered scene - you can extend or reduce the range of contrast in a scene through changes in development.

    Pushing and pulling development is a bit different, and usually relates to purposely exposing a film at higher or lower ISO than your normal EI, and then compensating with longer or shorter times.
    Your description of push-pull here sounds effectively like what a you do to when you adjust your light meter for your PEI if your development time happens to be off in the first place.
    Quote Originally Posted by DanK View Post

    3 - Once you test your film with your equipment, you may find that a 100 speed film rated at 100 doesn't give you the information in the negative you want. Adjusting this speed allows you to tailor the film speed to your equipment and process - many rate their film speed lower than rated - but again this is through testing.
    Isn't this the PEI?
    Quote Originally Posted by DanK View Post

    4 - Your meter reads 18% gray +- - it doesn't take into account the subject. Assuming you are using a spot meter - Metering a white wall and exposing at the indicated exposure at 'your' correct ISO will essentially record a gray wall on your negative, with normal printing - considered Zone V. Increasing exposure by two stops would record the white wall as Zone VII on your negative, and essentially print white, with normal printing. Same is true for Shadow detail - the meter will again show Zone V, and if exposed and printed normally will be Zone V in the resulting print. To place the shadow at Zone III, decrease the indicated exposure by two stops. The resulting negative when printed normally will be darker at Zone III.
    Yup. I have read 'The Negative'.
    Quote Originally Posted by DanK View Post


    Hope this helps...
    Getting closer. Thanks!

  7. #7

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    Re: PEI, Push-Pull, Exposure Confusion

    Quote Originally Posted by mmmdoughnuts View Post
    My two light meters are equivalent to about 1/3 of a stop. I have built a LED source and used an oscilloscope to time my shutters at each speed so I believe that I am (within 1/3 stop) dealing with just temperature and time now and I am starting to work with a step wedge to get the PEI right.


    I think this is exactly where my confusion is. Is 3) in reference to someone's PEI 1) or is someone pushing the film to get more grain and/or a different film curve for contrast 2))?

    Your description of push-pull here sounds effectively like what a you do to when you adjust your light meter for your PEI if your development time happens to be off in the first place.Isn't this the PEI?

    Yup. I have read 'The Negative'.

    Getting closer. Thanks!
    Andy,

    I don't think a step wedge will get you where you want to go, from reading your post. It might get you close, but a densitometer would be your best bet.

    Shutters and their accuracy are only one variable, of many.

    Exposure revolves around the low values, your testing will determine what film speed your equipment requires to record the low values where 'you' place them with your meter.

    Development times will adjust your highlight density in relation to your low values. Shorter development brings your high values closer to your low values, longer development places the high values farther from your low values.

    Everything is dependent on your low values....IMO/IME

    What you rate your film, expose, and meter will dictate your low values.

    Thanks,
    Dan

  8. #8

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    Re: PEI, Push-Pull, Exposure Confusion

    3 is your 1

  9. #9

    Re: PEI, Push-Pull, Exposure Confusion

    Quote Originally Posted by DanK View Post
    Andy,

    I don't think a step wedge will get you where you want to go, from reading your post. It might get you close, but a densitometer would be your best bet.
    Not sure I see your point. What does it matter if I use the shutter speed, aperture, ND filter or step wedge in front of the negative to stop down my zone V reading to zone I. Using a step wedge and exposing at zone V, in one shot, I know to what the ISO correction should be to get the zone I - it is just a matter of counting the step number that registers 1/3 step above fb+f in the negative.

  10. #10

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    Re: PEI, Push-Pull, Exposure Confusion

    For me, these concepts are associated with two different ways of working...

    1. The push/pull thing: You rate the film at something other than box speed and then "push" or "pull" the development, which just means adjusting the dev time according to some known values, like those published on the massive dev chart. Usually you pick pattern that is known to work already and yields a look you are going for, such as Tri-X 400 rated at 1600 and then pushed two stops (+2 in lab parlance) in dev. Love that myself.

    2. The zone system. This means you test your film to find out its true (not box) EI with your gear that will give you confidence that when you meter something and then "place" it in Zone III, it really is Zone three. You use zone system concepts for exposure and expansion/contraction of development time in order to get the precise contrast you want. Adams goes over this in loving detail in his book. It's all in there.

    So, while the ideas of altering the exposure and the dev time are in both ways of working, they really are thought about in two different ways to achieve two different types of results... usually. Number one is rock and roll and number two is Bach. I love rock AND Bach personally. But I personally rock with 35mm and MF, and I Bach with LF. Your mileage may vary; there are some cool pushed LF shots around the web.

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