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  1. #1
    coigach's Avatar
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    infrared filter comparison

    I'm sure I'm not alone in being annoyed by the numbering systems used by different manufacturers to describe their IR filters - very confusing.

    Can anyone post info / a link to a comparison of the most common IR filters, with the Wratten rating and the filter factor included to enable me to compare products accurately, and to work out my usable film iso.

    Cheers for your help,
    Gavin

  2. #2
    thebanana's Avatar
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    "While you're out there smashing the state, don't forget to keep a smile on your lips and a song in your heart!"

  3. #3
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    You need to know two things for starters: the film's sensitivity curve and the filter's transmission spectrum. Actually, you also need to know how much IR light is available in your scene too, but let's just assume that we are talking about sunny 16 nice spring light, rich in IR. Then you need to know the filter cutoff and how far out into the IR your film sees.

    Alas, the filter naming conventions are not logical. Red=29?!!! Why not call it 633?!! <sigh> Oh well, we're stuck with the names.

    To help you see what the different filters do, look at these data:

    http://www.beyondvisible.com/BV3-filter.html

    Note that the 93 cutoff is really too high for any current IR film on the market. It was suitable for HIE but with the Rollei IR and the efke, my filter factors were ridiculous. I use an 87, a 72, and deep red, those are my three standards now.

    Take those data and (mentally) overlay them with the spectral response curves for your film, and all will become clear. Note that if your filter cutoff is at the ragged edge of your films response, then there will be great uncertainty in your exposure, so... bracket like nuts, 2 stop intervals at least.

    Have fun!
    "Only dead fish follow the stream"

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  4. #4
    coigach's Avatar
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    In the past I've used 120 Efke 820 with a Heliopan 695 filter. I metered TTL with my Pentax 67II and after a lot of bracketing found that the best results were iso 0.75. Gulp...!

    Am planning on using my wee Contax G2 for a summer project on Edinburgh, and have got a Hoya R72 filter. Will be using Efke 820 again. The Hoya R72 looks darker than my Heliopan 695 so I'm scrabbling around trying to get some comparisons...!

    Cheers for your help,
    Gavin

  5. #5
    coigach's Avatar
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    Found this online:
    http://www.markerink.org/WJM/HTML/irfilter.htm

    Cheers,
    Gavin
    Last edited by coigach; 06-14-2009 at 02:05 PM. Click to view previous post history.

  6. #6
    keithwms's Avatar
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    The efke plus the 72 will require a filter factor of about 6-8 stops.
    "Only dead fish follow the stream"

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  7. #7
    coigach's Avatar
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    Quote Originally Posted by keithwms View Post
    The efke plus the 72 will require a filter factor of about 6-8 stops.
    Thanks for help.

    Cheers,
    Gavin

  8. #8
    RobertV's Avatar
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    For the Rollei IR 820/400 (iso 400 without filter) it's a factor 5 with most regular 89B (RG695nm) or 88A (RG715nm) Infra red filters.

    Here an example of this film:
    1/30S - f=4,0 Heliopan RG715nm Bay I infra red filter, iso 12.


  9. #9
    stradibarrius's Avatar
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    I too am trying to understand the "photo-speak"...when you speak of the factor 5, do you mean that the filter adds 5 stops?
    Keith, with the Rollei IR400, on a sunny 16 scene, how many stops would you add for an 89b filter?
    "Generalizations are made because they are generally true"
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    Barry
    Monroe, GA

  10. #10
    keithwms's Avatar
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    Barry I don't have an 89b, sorry. Can't say from experience. Robert's suggestions of +5 sounds good to me.

    Yes, a factor of 5 means 5 stops.

    Take care that sometimes the filter factors for yellow, red filters etc. are stated in increments of 0.3, where 0.3 means 1 stop (it's log2 base 10)... but with IR filters, now that HIE is gone, the factors really are anywhere from 5 to 13(!) stops, in my experience.
    "Only dead fish follow the stream"

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