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Thread: Filtering for a deep red filter

  1. #1
    Drew Bedo's Avatar
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    MTERING for a deep red filter

    I meter with a Minolta Autometer IV F, in incident mode or with a 5-deg spot attachment. I have had poor results in the past using a deep red filter and applying a filter factor . . .either I have a mental condition or too many fingers for counting with (while juggling the meter and fighting a dark cloth while choking on the loup's neck cord.)

    Can I just meter the scene through the filter to arrive at a workable exposure?
    Last edited by Drew Bedo; 24-May-2022 at 06:29.
    Drew Bedo
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  2. #2

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    Re: Filtering for a deep red filter

    Reading dark filters through different meter cells is asking for trouble... Different cells have a different response than film or transmission at their extremes, and from experience readings and exposure can been off using a TTL SLR of good camera makes... The type of cell also makes a difference...

    The easiest thing to do is to convert your ISO speed with your factor (in stops or etc) to new EI and just set to the new EI (like using your R25 filter with factor of 3 stops/your ISO 100 film becomes EI 25, and you enter that directly on your meter...

    Just don't forget to change your meter setting later when you change or remove filter...

    All of my filter cases are marked with the stop difference on label to ease some thinking too much while using...

    Steve K

  3. #3

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    Re: Filtering for a deep red filter

    Easiest way I know of is to do some basic tests. Start with the published/suggested filter factor and then open up about a half stop at a time for a few exposures. Develop and check the negatives and you'll get there.
    "My forumla for successful printing remains ordinary chemicals, an ordinary enlarger, music, a bottle of scotch - and stubbornness." W. Eugene Smith

  4. #4

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    Re: Filtering for a deep red filter

    I used to have a Zone VI modified meter, and metering through the filter worked well, at least through the mild correction filters I used. I rarely used the really strong ones, like a #25 or #29 red, and when I did, I bracketed my exposures.
    (Full disclosure- I lost that meter on a field trip some years back.)

  5. #5

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    Re: Filtering for a deep red filter

    Iíve always used the manufacturerís factor Ö itís always worked wellÖ. This is b&w after all , you donít need to nail it to better than 0.5 stop, even 1 stop in many cases. The manufacturer wonít be off by that much.

    A red filter will be in the neighborhood of 3 stops. Just double the meterís exposure 3 times and youíre fineÖ.

  6. #6

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    Re: Filtering for a deep red filter

    I typically use 3 f-stops for my deep read filter (B+W brand) - I have not had any problems. Check with the specific manufacturer info for your filter to see what filter factor / f-stop correction needs to be applied.

  7. #7

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    Re: Filtering for a deep red filter

    Quote Originally Posted by LabRat View Post
    The easiest thing to do is to convert your ISO speed with your factor (in stops or etc) to new EI and just set to the new EI (like using your R25 filter with factor of 3 stops/your ISO 100 film becomes EI 25, and you enter that directly on your meter...
    Wouldn't that be an EI of 12, not 25 for three stops from 100?

    My B&W 25 measures 2⅔ stops.

    Mike

  8. #8

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    Re: Filtering for a deep red filter

    Quote Originally Posted by mpirie View Post
    Wouldn't that be an EI of 12, not 25 for three stops from 100?

    My B&W 25 measures 2⅔ stops.

    Mike
    Correct!!! My bad... Didn't count one of my fingers...

    Steve K

  9. #9

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    Re: Filtering for a deep red filter

    I have a Zone Vi modified meter, and my experiences reading through a deep red filter always resulted in significant underexposure. Adding 3 to 4 stops of exposure instead hasn't been a problem. Try 3 stops as a test, adjust if necessary, and you'll be good.

  10. #10

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    Re: Filtering for a deep red filter

    I follow LabRatís Ďmethodí:

    Set the meter for the new EI and meter; it works, you donít need to calculate anything. I put a stycky tape on the meter as a reminder that itis set for the particular filter I am using.
    I have a modified Zone VI meter but this is simpler and quicker.
    Last edited by Renato Tonelli; 22-May-2022 at 07:58. Reason: sp

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