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Thread: A reciprocity cry for help.

  1. #1

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    A reciprocity cry for help.

    so I am new to LF and am using 4x5 Foma 100 (live in Germany so it is inexpensive). We took the camera out yesterday and it was a bumbling affair, no light meter, no watch, only a slight understanding of recip, and then the battery died in our Rollei...All in all an eventful day. with the DSLR we metered a shot for ISO 100, f22 at 15 secs and then my brain started to fry.

    I am technical in nature...doing IT for a living and used to fly for the US Army but when I look at Foma's chart:

    Schwarzschild effect
    Exposure (seconds) 1/1000–1/2 1 10 100
    Lengthening of exposure 1x 2x 8x 16x
    Correction of aperture number 0 -1 -3 -4

    I get that the exposure is a factor of ten but I have no idea how to fill in the blank spaces between 1, 10 and 100 seconds. I have scrounged the forum here and have read quite a bit on outside forums/websites that talk one through reciprocity so I grasp what is going on and why this is an issue but for the life of me I am not having the light bulb moment that will enable me to figure this out on my own.

    So I am approaching the forum, with me hat in hand, and am begging someone out there to enlighten me, provide a spark of some sort, so I can get through this and make some reciprocity charts.

    Many thanks

    Erick

  2. #2
    Vaughn's Avatar
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    Re: A reciprocity cry for help.

    How about putting the numbers on a graph and using it to get the in between times?

    Vaughn

  3. #3

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    Re: A reciprocity cry for help.

    that would work? for some stupid reason I was hung up that it was a logarithmic curve line...time to make some graph paper or buy it in the morning.

    Is it that easy?

    Thanks

    ./e

  4. #4
    Wayne venchka's Avatar
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    Re: A reciprocity cry for help.

    I can't help your aching head or fill in any blanks except to say that apparently Foma film has terrible recirocity compared to other films. I'm heading out this weekend with my first batch of Foma 200.

    Good luck!
    Wayne
    Deep in the darkest heart of the North Carolina rainforest.

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  5. #5

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    Re: A reciprocity cry for help.

    Quote Originally Posted by 77seriesiii View Post
    Is it that easy?
    Probably. See how the numbers fit on a graph. If it gives a reasonable-looking curve between the known values, you'll be safe enough interpolating.

  6. #6

    Re: A reciprocity cry for help.

    also keep in mind with photography everything is usally measured in stops and a stop is simply double or half the light of the stop below or above it.

    So in looking at your Foma numbers the difference between 10 seconds and 100 seconds is only 1 stop. In the real world (with B&W film anyway) you will not notice much if any difference if you are a stop off.

    I use a lot of film from Eastern Europe and for what it is worth I always err on the side of more exposure not less.

  7. #7

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    Re: A reciprocity cry for help.

    Before you get all bent out of shape over the proper reciprocity compensation, you need to do a lot of calibration of your film and equipment. You have to know what “Normal” is before you can make meaningful adjustments for reciprocity. Even with that knowledge, adjusting your exposure for reciprocity is largely based on judgment.

    Your chart states that if your meter tells you to use a 1 second exposure, you need to double that and expose for 2 seconds. At a reading of 10 seconds you need 8x the exposure and at 100 seconds you need to expose 16x. Between these benchmarks you can use graphs or mathematics or you can do what most of us do and make an educated guess. So if your meter indicates say 4 seconds, that’s a little less than half of the difference so I would expose for about 30 seconds. You may think that’s not very precise but keep in mind that my 4 second exposure was based on some very educated guesswork in the first place ( I chose what to meter and what part of the scene to place important values on) and the nature of reciprocity and how it reacts to different parts of the spectrum. Remember, reciprocity causes an increase in contrast because the high values in the scene are affected more by the increased exposure than the low values.

    Get a meter; calibrate your film and processing; understand the process and relax and make useful exposures based on educated guesses.

    Jerome

  8. #8

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    Re: A reciprocity cry for help.

    Quote Originally Posted by Wallace_Billingham View Post
    also keep in mind with photography everything is usally measured in stops and a stop is simply double or half the light of the stop below or above it.

    So in looking at your Foma numbers the difference between 10 seconds and 100 seconds is only 1 stop.................. ????
    I didn’t study NEW MATH but using old math, 10 seconds to 100 seconds is 3 ¼ stops.
    Jerome

  9. #9

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    Re: A reciprocity cry for help.

    Well, under the new math with reciprocity, it is probably not 3-1/4 stops.

  10. #10
    Vaughn's Avatar
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    Re: A reciprocity cry for help.

    Quote Originally Posted by 77seriesiii View Post
    Is it that easy?./e
    NO... I just tried to graph it several ways with no real luck -- found out I forgotten much of my math and graphing!

    I have a list of corrected times for Tri-X that Michale Kenna worked out -- if anyone knows long exposures, he does!

    Skipping some of his numbers...(first is metered exposure/second in corrected exposure)

    2sec/4sec.....10sec/50sec....40sec/240sec(4.5min)...80sec/630sec(10.5min)...3min/25min
    6min/60min...10min/120min...20min/4hours...40min/8hours


    Many of my exposures under the redwoods tend to be in the 5 to 30 minute range -- no wonder my shadows tend to drop out sometimes...LOL!

    Vaughn

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