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Thread: Focus Shift For Infra-Red

  1. #1
    Baxter
    Join Date
    Mar 2001
    Location
    Lymington, South Coast, UK
    Posts
    94

    Focus Shift For Infra-Red

    I am keen to try Mono IR film initially on 6x12 roll film back on my Ebony RSW (therefore no focus scale), before I try to source 5x4 sheet. I am not sure how to compensate for the focus shift once I've correctly set-up the shot in the normal way on GG. I normally take an SQA with me so might be able to use the focussing on this in some way.

    I shoot landscapes using 120mm and 90mm lenses and generally am looking for full front to back sharpness.

    I can't recall seeing any mention of this in the books I've read, but am prepared to buy books if necessary.

    Also in UK we are awaiting this years batch of Konica IR, are there any other films in 120 (and 5x4) which I ought to consider.

  2. #2

    Focus Shift For Infra-Red

    Keep in mind I have not used the IR film you mention, nor any LF IR film, but am very familiar with the Kodak 35mm version, having used it constantly for 15 years.

    I would not worry about focus correction unless you are using a visually opaque deep red filter or are doing closeups with limited depth of field. Visual light and infrared light sometimes focus at a different place because the wavelengths are different (IR waves are longer). But unless you're using one of those opaque IR filters, your exposure will be a mixture of both kinds of light. So if you're using a medium red (recommended for most applications) or orange or yellow filter, and you correct for IR, then the visual light may be off. A decent amount of depth of field will take care of both.

    The Konica film (also the Ilford SFX) is not a true infrared film - it's red sensitive, but not very far into the IR spectrum. So you don't have to do any focus correction for that, even with the opaque filter.

    It is more important to bracket for exposure than adjust for focus.

  3. #3

    Join Date
    Oct 2000
    Posts
    213

    Focus Shift For Infra-Red

    I thought Konica was out of the IR business. Does anyone know if it will in fact be available? Thanks, Steve

  4. #4

    Join Date
    Oct 2001
    Posts
    7

    Focus Shift For Infra-Red

    Baxter -

    The only IR film I'm aware of is MACOPHOT IR 820c Infrared film, available in both 4 x 5 and 120 sizes. It has different characteristics from the Kodak HIE film, but is a useful substitute. I had heard that Konica had planned to stop making their IR film as of late 2000, but found some in stores in May, 2001.

    As for focusing, the books I've read aren't real helpful either. Typically with large format, stopping down to f-22 or smaller should reduce the out-of-focus problem. Given that you appear to be using wide angle lenses, you may be able to get away with a wider aperature.

    Best of luck.

    Dave

  5. #5

    Join Date
    Mar 2001
    Location
    Nanaimo B.C.
    Posts
    17

    Focus Shift For Infra-Red

    Not sure why this morning's post did not materialize.

    Hello Baxter,

    Since IR has a longer wavelength you need to adjust your focusing a smidgen. If I remember correctly, the formula is .0025 % (1/400) of the focal length which should bring the infrared image into sharp focus. I normally have no problem with sharpness as typically set my aperature around f22 on 4x5 as well as 6x7 (f16) and do not adjust my plane of focus. Also consider looking at Maco 820 as it presently comes in 4x5 and no ther IR film is commercially available in that format. Both Konica and Maco are fine grain and slow compared to HIE. You may find someone has some frozen some 4x5 HIE and sells it periodically proir to being discontinued by Kodak.

    If you plan to get into IR, I suggest the following site to learn about experiences of others as well as a plethora of technical info. Everything you wanted to know about IR but were afraid to ask.....

    http://www.cocam.co.uk/CoCamWS/Infrared/INFRARED.HTM

    Cheers,

    Chet

  6. #6

    Join Date
    Mar 2001
    Location
    Nanaimo B.C.
    Posts
    17

    Focus Shift For Infra-Red

    I forgot to mention that I have experimented with many of the various infrared "type" films" and various developer combinations and for those that want to shoot HIE in a 120 format (cut down from 70MM) or for that matter 220 HIE. My source for this film can be located at:

    http://infrared.homestead.com/

    I do not want to provoke a discussion on IR but what sets HIE apart from the other films (in addition to degree of IR spectrum) in the lack of an antihahlation backing on the film. With certain developers and appropriate dilutions Konica and Maco can be developed to approximate the "wood effect" etc.... IMHO... good luck to all. Baxter, KOnica IR can be loaded in normal light but HIE primarily in total darkness unless your source of film is at the URL above where subdued lighting works very well based on my limited experiences. Cheers, Chet

  7. #7

    Focus Shift For Infra-Red

    Chet, what do you mean by the "wood effect?" Is that a typo? The "wool" effect maybe? The "good" effect?" the "mood" effect? I'm being silly but I never got any "wood" effect with HIE.

    The word "effect" is starting to look a little strange too.

    Cheers,

  8. #8

    Focus Shift For Infra-Red

    I`ve solved the problem of focus shift in this way:

    put the Kodak Wratten No. 87C an the lens, focus the sun - it works fine! Then m ark your lens extension - pictures of landscape are shape.

    I have't any problems with Kodak IR Sheet film and even the old ORWO I 950 Platt e has the right sharpness!

    There is one problem: some people (not colour-blindly!) (are not able to see the red light which is coming through the filter (it depends on your seniblity of y our eyes).

    Mark Kallfass

  9. #9

    Focus Shift For Infra-Red

    Sandy, The "Wood effect" is what you call the lightening of foilage in IR. It is named after the guy who discovered it. Check WJ's Infrared Page for lots and LOTS of info.

    www.a1.nl/phomepag/markerink/mainpage.htm

  10. #10

    Join Date
    Mar 2001
    Location
    Nanaimo B.C.
    Posts
    17

    Focus Shift For Infra-Red

    Trees and grasses appear to glow white and radiate when illuminated by an IR light. This effect is often called the ?Wood Effect.? It doesn?t refer to wood but to R.W. Wood, a pioneer in the field of infrared film. Wood actually is fairly dark on IR film.

    Cheers

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