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Thread: Exposure compensation for small apertures

  1. #41

    Join Date
    Jul 2008
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    Re: Exposure compensation for small apertures

    Mechanical shutter are lesser accurate-precise by their innate workings. Thus was born the electronic shutter which improved this in various ways.

    The alternative method to achieve accurate-precise exposure of film is to used high quality electronic strobe-flash which is not nearly as dependent on shutter open-close times. Or why this was the overly preferred method of color transparency film exposure required for proper high quality color transparency image work back in the day. A properly calibrated and stable electronic flash system of lens aperture, film batch tested for actual film speed and all related produced consistent and reliable image results to 1/3 f-stop or better.


    Bernice


    Quote Originally Posted by Tin Can View Post
    I notice some want 1/3 stop accuracy with film aperture and shutter speed

    What is the ANSI spec?

    Maybe plus/minus 30 percent!

  2. #42
    Tin Can's Avatar
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    Re: Exposure compensation for small apertures

    I know most disparage my 4 Paul C Buff Einsteins, they are what I could afford

    But I can precisely adjust them using my Sekonic L758 without rechecking IRL flash exposure

    I do like that
    Tin Can

  3. #43

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    Re: Exposure compensation for small apertures

    Quote Originally Posted by Tin Can View Post
    I notice some want 1/3 stop accuracy with film aperture and shutter speed

    What is the ANSI spec?

    Maybe plus/minus 30 percent!
    Randomly selected from random LF shutter service manuals (Graphex and Synchro Compur):

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    Attached Thumbnails Attached Thumbnails Capture3.JPG  

  4. #44
    Drew Wiley
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    Re: Exposure compensation for small apertures

    Little exposure errors can add up fast. For color transparency usage, even a third of a stop might be objectionable if one is working on the edge of contrast limits.

  5. #45

    Join Date
    Feb 2009
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    279

    Re: Exposure compensation for small apertures

    Unfortunately, I see too many naive people here thinking they don't need to take their shutters' efficiency into consideration since they do not use the 1/500s speed.... Sorry that's not correct. The difference in shutter efficiency is insignificant at speeds about 2 stops longer then the longest speed that is 50% efficient, i.e. 2 stops slower than the longest speed at which the shutter blades open and immediately close, without any time gap. With different shutters, those slowest 50%-efficient speeds differ a lot. It is a 1/200s on my dial-set Compur #2 but it is a 1/50s on my Ilex #4, and it is a 1/15s on my Prontor-Press #1. That means I can forget the efficiency issue with all speeds from 1/50s and longer with my Compur but only with the 1/10s and longer with my Ilex and only from the 1/4s and longer with my Prontor-Press. A 1/10 and a 1/4 are not the shortest speeds usable in LF....

    (That also means that those published exposure compensation tables for a 'general shutter' just can't be correct. Because there are no 'general shutters' in the real world.)

    And another point: what I have read in special technical literature is that shutters are usually calibrated to make their speeds accurate at 2 f-stops smaller than the maximum aperture, not wide-open. That way the effective speed deviations are smaller at all the rest f-stops.

    But still no exposure compensation is actually needed for a film like Tri-X....
    Last edited by ridax; 11-Sep-2022 at 01:50. Reason: more info addd

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