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  1. #1
    EASmithV's Avatar
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    Yashica Mat and Infared - focus adjustment?

    Hello all,

    I am considering making my Yashica Mat an infrared only camera, or at the very least shooting a good deal of infrared with it. I've shot about 3 rolls so far, and they look great, especially portraits... However, I have a problem. Shooting wide open at 1/60th is often my perfect exposure, however, that gives me little or no depth of field and at close distances the focus error becomes evident. I know I could use a tripod and stop down, but I'd ideally like to keep the ability to handhold. Is there a way to adjust for shooting infrared? I don't see a dot on the focus knob. Also, would it be feasible to have someone shim the GG for infrared? Or would it be easier to just back focus all my shots a bit? How much, if so? I want to be able to go all analog with my shots but it seems they need heavy sharpening using alternative techniques to get good images...

    thanks
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
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    RIP Kodachrome

  2. #2

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    infrared marks don't seem to be as common as they once were -- i found one on my 50-year-old summicron 50, but not on the rolleicord or yshicaflex.

    Where it is found it is usually a titch to the right of the zero point so that when you move to it, yu actually focus a bit closer to allow for the different focus point of the infrared light. Perhaps lenses are better correctd and the mark is no longer needed? Or only needed for longer lenses where the depth of field is more critical?

    I'd do a test, shoot half a roll focusing dead on, and half a roll adjusting each shot 1 mm to the right (closer) on the focusing dial and see what comes out.

  3. #3

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    You could try finding a Rollei Infrarot filter which is supposedly optically compensated for the focus shift on a TLR; they should exist in Bay I. Changing the relative focus of the viewing lens might work in theory, but it would be quite a delicate operation, and would certainly require a collimator.

  4. #4
    EASmithV's Avatar
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    Wait.... Rollei made a focus shifted corrected filter thingy?! Does it work? What is the IR cutoff?
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
    http://www.flickr.com/easmithv/
    RIP Kodachrome

  5. #5

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    The Minolta Autocord had a red arrow on its focus lever for infrared focus. I made a composite of shots form someone who asked about this. It might give you a good starting point as to what the compensation is?

    http://www.flickr.com/photos/1806725...57624555271098

  6. #6
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    I have used my 124G with an 89B (695 nm cutoff) and didn't really worry about it; unlike the earlier IR films, the light spectrum for today's IR films barely extends outside the visible spectrum and as such I don't think compensation is that important. Now I admit that is an opinion, not carefully researched fact.

    That said, I think on many lenses the IR adjustment amounts to using approximately the next depth of field mark toward closer focus as the indicator mark.
    Last edited by DWThomas; 01-23-2013 at 11:01 AM. Click to view previous post history.

  7. #7
    EASmithV's Avatar
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    Quote Originally Posted by DWThomas View Post
    I have used my 124G with an 89B (695 nm cutoff) and didn't really worry about it; unlike the earlier IR films, the light spectrum for today's IR films barely extends outside the visible spectrum and as such I don't think compensation is that important. Now I admit that is an opinion, not carefully researched fact.

    That said, I think on many lenses the IR adjustment amounts to using approximately the next depth of field mark toward closer focus as the indicator mark.
    I'm shooting handheld ir portraits and they are focus critical, I'm getting clearly unsharp results at close distances. I'll try the dof trick. I wish ir film wasn't more expensive.
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
    http://www.flickr.com/easmithv/
    RIP Kodachrome

  8. #8

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    Yashica Mat and Infared - focus adjustment?

    I managed to find the Rollei IR filter in bayonet 1 size for my Rolleicord. It was new and came from Mr Cad in Croydon England. It was expensive( about 50GBP). It is quite opaque, like an IR720 and gives good results with the Rollei film. I have heard that it is "focus-corrected" but I have never seen this in any Rollei publication. I have used it for landscape, and therefore have not seen the effect with the lens at large apertures. The shots I have are in focus without making any adjustment. In many ways the TLR is the ideal IR camera as you can work with the filter in place and see to compose/focus.

  9. #9

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    Quote Originally Posted by Alex Muir View Post
    I managed to find the Rollei IR filter in bayonet 1 size for my Rolleicord. It was new and came from Mr Cad in Croydon England. It was expensive( about 50GBP). It is quite opaque, like an IR720 and gives good results with the Rollei film. I have heard that it is "focus-corrected" but I have never seen this in any Rollei publication. I have used it for landscape, and therefore have not seen the effect with the lens at large apertures. The shots I have are in focus without making any adjustment. In many ways the TLR is the ideal IR camera as you can work with the filter in place and see to compose/focus.
    The 1960 edition of Rollei: The Practical Accessories mentions "ground-in focus compensation." What that means in practice, well, who knows.

  10. #10

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    Yashica Mat and Infared - focus adjustment?

    I have found some information on the Rollei IR filter which confirms the cut-off value as 700m/u. Unfortunately, this source gives no more information to clarify the effect of the focus correction.

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