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Thread: Using 25A filter with IR modded 40D

  1. #1
    Senior Member denniskee's Avatar
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    Default Using 25A filter with IR modded 40D

    Hi guys

    Recently just got my EOS 40D modded for IR by non other than fatigue. When comparing to without using any filter on the lens & camera on AV mode :

    Tried CP with it (though internet say no effect, but what the heck, have it use it lor):
    Color shifted
    No cutting of reflection in windows
    Needs to compensate 1/3stop less.


    But when I tried 25A:
    Color didnt shift
    Needs to reduce 2stops exposure compensation

    Any idea y so much difference in the metering?
    photography makes one sees things from all angles.

  2. #2

    Default Re: Using 25A filter with IR modded 40D

    For 25A (RED) compensation is about there = 2 stops.For CPL because it passes all light spectrum (for IR so..)

    Filters blocks and passes certain light spectrum and the energy wavelengths differ.There is a calculation method called filter factor which is not the same as F stops but translate to it.
    Below are links that explain what it is and the calculation of it.Google black and white filters to know more.

    https://en.wikipedia.org/wiki/Filter_factor

    http://www.schneiderkreuznach.com/fi...mpensation.pdf

    https://ipotpourri.wordpress.com/201...ography-table/

  3. #3
    Senior Member denniskee's Avatar
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    Default Re: Using 25A filter with IR modded 40D

    Thanks one eye jack, will read through the link!!
    photography makes one sees things from all angles.

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