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  1. #1

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    ULF reciprocity quandary

    I've recently started shooting some Efke PL25 in 11x14, the lighting conditions I'm shooting in routinely put me in 4, 6 and 8 minute exposer times. Part of the long exposer times I'm experiencing is because of depth of field issues in ULF, I usually have to stop down to f90 or f64 minimum.

    J&C list reciprocity times as follows:
    Efke PL25/50 Suggested Reciprocity Adjustments

    to 1/2 second - 0 stop

    1 second - 1/3 stop

    10 seconds - 2/3 stop

    100 seconds -*1.5 stops

    At a 4 minute exposer I'm already at 240 seconds and going down probably more than three stops (f45) which does not help me.

    I would much rather extend my exposer time than mess with my already small f-stop scale.

    Is there any way to accurately figure out extended reciprocity times from the above tech info provided by J&C?

  2. #2

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    Exposure is a condition of the time the lens is open and the size of the lens opening. That is true of reciprocity just as much as a normal exposure.

    If you are at four minutes then a one and one half stop adjustment would be ten minutes.

    Not that it makes any difference to me but why are you using Efke 25 with an 11X14 negative? Most people who shoot big sheets of film shoot fast film for the reasons you mention.

  3. #3

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    Quote Originally Posted by Donald Miller
    Exposure is a condition of the time the lens is open and the size of the lens opening. That is true of reciprocity just as much as a normal exposure.

    If you are at four minutes then a one and one half stop adjustment would be ten minutes.

    Not that it makes any difference to me but why are you using Efke 25 with an 11X14 negative? Most people who shoot big sheets of film shoot fast film for the reasons you mention.
    Thanks Donald, I grabegrabbed stuff up from J&C for two reasons. First, I heard about some of its characteristics and wanted to see how it would behave. Second, I'm a cheap impatient bastard that couldn't waite another promised month for the PL100 that will never be cut to size.

    Is there some where here or anywhere else that well tell me how to formulate the conclusion you came to here? {If you are at four minutes then a one and one half stop adjustment would be ten minutes.}

    Mike

  4. #4
    scootermm's Avatar
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    mike
    my suggestion would be to do some testing (I know it sounds expensive) but given the differences in developing that each person has in their work method. Maybe say, if you get a meter reading of 30secs at F45... try exposing for say 2mins and 4mins and develop them identically. See which gives you the best exposed negative.
    my experience has been that a 30sec meter reading requires a 2mins exposure. a 4 min meter reading would need approx 30-40mins. But like I said prior, often times peoples developing techniques, developers, trays v. rotary, etc, all this stuff can likely play a part in it.
    not exactly a literal answer to your question, but it might be a good idea to do some testing, and would likely be worth the sheets of film.

  5. #5

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    Quote Originally Posted by Mike A
    Thanks Donald, I grabegrabbed stuff up from J&C for two reasons. First, I heard about some of its characteristics and wanted to see how it would behave. Second, I'm a cheap impatient bastard that couldn't waite another promised month for the PL100 that will never be cut to size.

    Is there some where here or anywhere else that well tell me how to formulate the conclusion you came to here? {If you are at four minutes then a one and one half stop adjustment would be ten minutes.}

    Mike
    Mike since stops are the doubling or halving of exposure...and since exposure can be a measure of time or of the size of the lens aperture, then a one and one half stop adjustment to a four minute exposure time would be one stop...an additional four minutes and one half stop an additional two minutes. These are added to your base time of exposure to arrive at ten minutes.

    I haven't used this film myself so I don't know if these are accurate reciprocity adjustments. However, I respect the products and information that John at JandC provides.

    In reciprocity situations, it is also wise to adjust development. This is due to the nature of an exposure having various luminance levels under reciprocity conditions. The more luminous regions of the exposure would receive proportionally more exposure then the darker areas. So this leads to an exposure having more inherent contrast then one would normally assume. As the length of the exposure increases and the reciprocity adjustment increases then the development time is adjusted in ever incremental amounts. Of course since the length of exposure and reciprocity adjustment add increasing amounts of contrast then the development time is adjusted downward to compensate.

    As an example of the adjustment, Kodak makes the following recommendations of adjustments to developing time for their film Tri X under reciprocity conditions. For one stop of reciprocity adjustment, decrease development by ten percent. For two stops of reciprocity adjustment decrease development by twenty percent and for three stops of reciprocity adjustment decrease development time by thirty percent. These times and adjustments should be considered as starting points.

    By the same token, I think that it is improper to assign garden variety reciprocity adjustments to all films. Each film will have it's own characteristics. For instance TMax 400 is noted for it's excellent reciprocity characteristics and if the adjustments previously ascribed were used you would end with a negative that would be over exposed to the point of being unuseable.

  6. #6

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    Thank you Matt and Donald, I think this might indeed burn a couple or more sheets of film. Testing as Matt suggested along with Donalds reciprocity explanation seems to be my only option.

    Mike

  7. #7

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    Quote Originally Posted by scootermm
    my experience has been that a 30sec meter reading requires a 2mins exposure. a 4 min meter reading would need approx 30-40mins.
    I have similar timings.
    And don't forget to incorporate longer exposures for the bellows extention before computing the reciprocity correction.

    Close-ups metered at 30" quickly become 10'.

    G

  8. #8
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    Mike, I think I may have made a suggestion of getting a box of 4x5 Efke 25 to try with your processing trials, if not I apologize. I would still rather you work out the numbers with 4x5 to see what happens than using a very large film in unknown territory. Best, tim

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    Quote Originally Posted by noseoil
    Mike, I think I may have made a suggestion of getting a box of 4x5 Efke 25 to try with your processing trials, if not I apologize. I would still rather you work out the numbers with 4x5 to see what happens than using a very large film in unknown territory. Best, tim
    Yeah, working with smaller film for testing would be my advice as well. You can even cut a larger sheet into pieces and tape it into the film holder, only make sure to tape opposing edges so film curl doesn't catch the darkslide and pop it off (happened to me once).

  10. #10
    David A. Goldfarb's Avatar
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    Or, if you're too impatient to order some 4x5" and don't have the ability to cut down a sheet of 11x14" precisely, you can make a test strip for exposure in camera by pulling the darkslide a couple of inches at a time for whatever interval makes sense for your test. Maybe start with the metered exposure plus one stop, say, and pull in one minute intervals, or you can make the strips vary by a half stop each if you calculate it in advance remembering that the last strip will have the shortest exposure. Or alternately start with the darkslide out and insert it a few inches at a time--whatever's easier.

    Once you figure out a base exposure for reciprocity, you can run development tests for contrast.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
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