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Thread: Infra-Red Film

  1. #11
    Ed Sukach's Avatar
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    [Not quite true. Konica 750 has a "bi-modal" sesitivity curve with one "peak" at something like 550um, and the other "IR" peak at 750um. Both peaks are uniform (they look like semi-circles) so there is an amount of sensitivity out to ~ i don't know .... 850um or so.]

    You guys are slipping. I mistakenly labeled the wavelengths as "um" - or "micrometers".... Ooops!! Should have been "nM" or "nanometers". Not much of an error ... only one thousand times (1000X).
    :roll:
    Carpe erratum!!

    Ed Sukach, FFP.

  2. #12
    Ole
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    Quote Originally Posted by Ed Sukach
    You guys are slipping. I mistakenly labeled the wavelengths as "um" - or "micrometers".... Ooops!! Should have been "nM" or "nanometers". Not much of an error ... only one thousand times (1000X).
    :roll:
    I was not slipping - I slipped out to test MACO IR820c instead. With 89B filter. May post results, if I find them worth it
    -- Ole Tjugen, Luddite Elitist
    Norway

  3. #13
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    I exposed close landscape scenes with Konica IR at EI=12 through a Wratten #29 (deep red filter -I wanted no colors other than far red and infra recorded). I might have used 8 except my spot meter won't set that low. I will admit some trepidation in focus due to the shift, but I used the setting on the KO 90mm Hexanon and a wag as to the foreground/ background dof. A tripod was essential (as usual). I'll admit to doing a little bracketing. Development was in D76 1:1, 8-1/2 minutes, 20 deg. C., (according to data found in the Massive Development Chart).
    Everything is in relatively sharp focus. The dream-like feeling
    is there without that fuzzy-wuzzy pictorialistic "look" which I find
    disturbing. I am also surprised at Konica's tonal range. The negative is a
    bit harder to print than I first believed. The tonal range (11+ zones?)
    exceeds the ability of the VC paper to produce a "straight" print of
    "normal" values. I had to use a Kodak #3 filter and then do a bit of
    dodging and burning. I gotta get a web site to show these things. I have
    put some prints on APUG and maybe I'll post one of these prints in the Technical Gallery soon - if the computer doesn't die and the scanner and.... Boy chemical photography is GREAT!

    Truly, dr bob

  4. #14
    sparx's Avatar
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    I have just aquired a roll of Konica IR750 35mm for my course project. I am rating it at iso 100 (approx f5.6 @1/60th according to my camera) but am a bit concerned about this focus shift as my lenses (Olympus OM) don't have a IR mark.

    My 28mm probably won't be too much of a problem because of its large depth of field but i was hoping to take some shots using a 70mm and a 200mm as well. Does the shift pull the focal point towards the camera or away?
    [size=1]the all new darkplanet photoblog[/size][size=1]
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  5. #15
    Ole
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    IR "bends" less in the lenses, so it isn't focused as much. That means that you have to pretend the subject is closer to your camera - so you focus closer. Fortunately you don't have to force your lens helical past infinity...
    -- Ole Tjugen, Luddite Elitist
    Norway

  6. #16
    Ed Sukach's Avatar
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    Quote Originally Posted by Ole
    IR "bends" less in the lenses, so it isn't focused as much. That means that you have to pretend the subject is closer to your camera - so you focus closer. Fortunately you don't have to force your lens helical past infinity...
    This is true, at least in theory. Lately I have been experiencing trouble with IR focusing ... I religiously focus and reset to the IR (red line) on the Hasselblad lenses (the older ones) --- and ... I'm obviously "out of focus".

    I've been thinking ... with films that are primarily sensitive to "far" (comparatively) Infra - Red (i.e., Kodak HIE) and filters that cut off light in the visible spectrum - this IR index probably made sense - but with the "near" IR films - Konica 750, Maco 820, Ilford SFX, and what was Agfa's -- and the use of mild filtration ... R25 ... I don't think there is that much of a "shift". Seems to me, the focus of the image we see through the viewfinder (filtered) is probably *very close* to what will be recorded on the film.

    I notice that there is *no* IR Index on the new Hasselblad lenses - which would seem to bear this out.

    "Next" technical task - to "wring this out".
    Carpe erratum!!

    Ed Sukach, FFP.

  7. #17
    Ole
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    Ed, you are perfectly right.

    The IR index mark is fo "real" IR, while most of "us" use "deep red" which behaves about like ordinary red light. Even with an 89C filter on MACO IR820 I could see no sign of focus shift using a 150mm APO-Lanthar lens, and very, very little with a 150mm Symmar.

    With any film except Kodak HIE and the very darkest filters, ignore the focus mark - except if it is very far from the infinity mark. Lenses are different, some are better corrected than others. APOs should be very close to no correction even in the worst-case scenario.
    -- Ole Tjugen, Luddite Elitist
    Norway

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