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Thread: IR 760 filter - rating film speed

  1. #11

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    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Bob Salomon View Post
    And how much IR is present under the shooting conditions.
    Bob, let me add that also what IR reflectance our subject has...

    Vegetation reflects around 8 times more the IR than the visible

    Click image for larger version. 

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    http://gsp.humboldt.edu/olm_2016/cou...flectance.html

  2. #12
    (Shrek)
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    Re: IR 760 filter - rating film speed

    I have shot Konica imagesetter film with filters up to 820nm, I used an old Pentax V spotmeter for exposure calculations. I simply held the filter up to the spotmeter and shot through it, then applied a correction factor to get exposures. The imagesetter film has a very narrow exposure range, it was the only way I could consistently get proper exposures.

  3. #13

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    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Pere Casals View Post
    Bob, let me add that also what IR reflectance our subject has...

    Vegetation reflects around 8 times more the IR than the visible

    Click image for larger version. 

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    http://gsp.humboldt.edu/olm_2016/cou...flectance.html
    Pere, I was in the 363rd Rec Tec squadron. We did most of the Cuban Crisis pictures that you have seen. Many were IR color and B&W. These shots in color easily showed camouflage vs live leaf color as the IR reflection created different colors. In B&W you could easily see where vehicles HAD been parked and how large they were and make educated guesses as to what they might have been carrying. This was because the temperature where they had been parked was different then the surrounding area.

  4. #14

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    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Bob Salomon View Post
    These shots in color easily showed camouflage vs live leaf color as the IR reflection created different colors.
    Yes, Aerochrome...

    "Kodak Ektachrome Infrared Aero Film and Ektachrome Infrared EIR. The first version of this, known as Kodacolor Aero-Reversal-Film, was developed by Clark and others at the Kodak for camouflage detection in the 1940s. The film became more widely available in 35mm form in the 1960s"

    I guess that it has the red sensitive layer also sensitized (extended) for the IR, so IR from vegetation exposes the red sensitive layer.


    There is a dedicated Aerochrome shop !!!

    https://www.aerochrome.shop/
    https://web.archive.org/web/20191106...rochrome.shop/

  5. #15

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    Re: IR 760 filter - rating film speed

    Thanks for the very interesting replies.

    The only reason I got the IR 760 is that it's the only one they have in the 49mm size. My preference was for the 720nm which I have in 67mm. I'll cut up some Rollei IR 400 film and tape it into some 4x5 holders and run some tests. Thanks again.

  6. #16

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    Re: IR 760 filter - rating film speed

    Can't you simply use a step-up ring to fit your 67mm filter on your 49 thread lens?

  7. #17

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    Thumbs down Re: IR 760 filter - rating film speed

    I tested some Rollei IR400 with the 760 filter at various speeds down to ASA 1.5 (sample at left). On the right is the same film exposed through a 720 filter. Clearly the 760nm filter is outside of the film's rating as Pere noted earlier, and even at ASA 1.5 is underexposed and therefore unusable in my opinion. I do like the film and will get a 720 filter which I know works well with it. Thanks for the helpful comments.

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  8. #18

    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Barry Kirsten View Post
    I tested some Rollei IR400 with the 760 filter at various speeds down to ASA 1.5 (sample at left). On the right is the same film exposed through a 720 filter. Clearly the 760nm filter is outside of the film's rating as Pere noted earlier, and even at ASA 1.5 is underexposed and therefore unusable in my opinion. I do like the film and will get a 720 filter which I know works well with it. Thanks for the helpful comments.

    Click image for larger version. 

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    Well, not completely out of the film’s sensitivity, otherwise you would have had no image at all. You will just need to add a stop or two when using that filter.
    --- Steve from Missouri ---

  9. #19

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    Re: IR 760 filter - rating film speed

    Quote Originally Posted by scheinfluger_77 View Post
    Well, not completely out of the film’s sensitivity, otherwise you would have had no image at all. You will just need to add a stop or two when using that filter.
    Probably most of the exposure was made by light not reaching 760nm that was not well blocked by the filter.

    See the filter marketed as "760" , it allows to pass a substantial light amount from 700 to 760. If it was a filter like this then 95% of the exposure could have been done by light not reaching 760nm.



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  10. #20

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    Re: IR 760 filter - rating film speed

    Thanks Steve and Pere. Yes there was some exposure probably below 760, but even exposed at ASA 1.5 it's probably close to 2 stops underexposed, so in practice unusable with this film I'd say.

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