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Thread: 4 x 5 focus problem

  1. #11

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    Re: 4 x 5 focus problem

    thanks all, I'll recheck my focusing and try a B&W test with a ruler to check the neg/GG alignment

  2. #12

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    Re: 4 x 5 focus problem

    Quote Originally Posted by LotusEsp View Post
    any suggestions on a good loupe?
    In a nutshell, Bob Salomon has nailed the requirements very well.

    You will find many different magnification factors of various loupes available. I have used 2x, 4x, 5x, 6x, 8x, and I have some 12x to 18x loupes that are for another industry. The best loupe magnification that works easiest for me on a GG for view cameras is the 4x magnification. I own and have used a 2x magnification loupe often with very good results.

    If you start to go much higher than 6x magnification, then things are generally a bit harder to focus the image super clearly. 8x is starting to get a bit hard, above that I have found focusing much harder. Doesn't mean you cannot use a high(ish) magnification, you certainly can, but you are focusing on an increasingly smaller area.

    I have a Schneider 4x with opaque and semi-opaque and that is very good. However round loupe bases are a bit problematic for getting alongside the GG edge and especially into the corners.

    To that end, I eventually purchased a Peak 4x square based loupe, best thing I have done for focusing, works a treat.

    The better loupes all have a dioptre adjustment ring, whereby you adjust the focus so that your eyesight is corrected. That adjustment ring is really a requirement, not a luxury.

    Attached is a picture of the Peak loupe that I have.

    Mick.

    Click image for larger version. 

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  3. #13
    Tin Can's Avatar
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    Re: 4 x 5 focus problem

    Is it possible to miss focus with any loupe-eyesight combination? If the image looks sharp and in focus on GG with any Loupe is it not in focus? Of course if the GG is out of spec positionly that IS the problem.

    I try many loupes and simple bare -7 diopter eye works OK at very close distance, but I have checked GG postion against holder actual and found some issues with some famous gear. Get a depth gauge and learn to use it. Or make a couple go no go sticks. Learn the stack up issue. http://www.sigmetrix.com/tolerance-stack-up/
    Tin Can

  4. #14
    Jim Jones's Avatar
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    Re: 4 x 5 focus problem

    Randy's link to the stack up issue is particularly applicable to film holders and ground glasses. Consider the linear position of the film within the holder. The "T" distance, between the face of the holder and the septum in a 4x5 holder is 0.197 +/- 0.007". The width of the slot for the film is 0.012". The film I have used varied from 0.004" to 0.010". Assuming the dimensions of the holder and film are barely within specs, the emulsion could be from 0.194" to 0.216" from the face of the holder. Ground glass position error and any deviation from perfect flatness of the film adds to the potential for unsharpness. To further complicate the problem, film may record more detail than can be seen on the ground glass, and it is easier to analyze sharpness on film than on a ground glass.

    This may sound discouraging, but photographers have managed to achieve sharp 4x5 negatives for more than a hundred years. Some even dare to use Aero Ektars wide open, although an acceptable depth of focus may well be smaller than the above worst case film position error. It's ironic that sheet film with all of its potential for error has almost completely replaced the more precise glass plates in vogue when typical lens apertures were smaller and contact printing was the norm.

  5. #15

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    Re: 4 x 5 focus problem

    Quote Originally Posted by Jim Jones View Post
    Randy's link to the stack up issue is particularly applicable to film holders and ground glasses. Consider the linear position of the film within the holder. The "T" distance, between the face of the holder and the septum in a 4x5 holder is 0.197 +/- 0.007". The width of the slot for the film is 0.012". The film I have used varied from 0.004" to 0.010". Assuming the dimensions of the holder and film are barely within specs, the emulsion could be from 0.194" to 0.216" from the face of the holder. Ground glass position error and any deviation from perfect flatness of the film adds to the potential for unsharpness. To further complicate the problem, film may record more detail than can be seen on the ground glass, and it is easier to analyze sharpness on film than on a ground glass.

    This may sound discouraging, but photographers have managed to achieve sharp 4x5 negatives for more than a hundred years. Some even dare to use Aero Ektars wide open, although an acceptable depth of focus may well be smaller than the above worst case film position error. It's ironic that sheet film with all of its potential for error has almost completely replaced the more precise glass plates in vogue when typical lens apertures were smaller and contact printing was the norm.
    Thats a very good point. All the talk of tolerances yet people have been getting sharp images for many years before I came alone with my fat fingers.

    I did another loupe test last night, and found that I was looking at the ground side (closest to the lens) of the GG, not the smooth side. There are black lines etched into the ground side and these focus up with the grain

    When I get time I will burn some B&W and try the ruler test. I should also check my scanning process.

  6. #16
    Jac@stafford.net's Avatar
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    Re: 4 x 5 focus problem

    Quote Originally Posted by LotusEsp View Post
    I did another loupe test last night, and found that I was looking at the ground side (closest to the lens) of the GG, not the smooth side. There are black lines etched into the ground side and these focus up with the grain.
    That is the correct method. If you want to make life a bit more complex, but get accurate focus, consider aerial focusing. You can have the GG drilled to make it so.

  7. #17

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    Re: 4 x 5 focus problem

    thanks Jac
    are there any walk through of aerial focusing? I've been searching but can only find vague referencing to the process, drilling holes, using thin wire etc. Nothing comprehensive

  8. #18

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    Re: 4 x 5 focus problem

    Quote Originally Posted by Randy Moe View Post
    Is it possible to miss focus with any loupe-eyesight combination? If the image looks sharp and in focus on GG with any Loupe is it not in focus? ...
    Randy, I think you're right here. I've used cheap loupes turned backward, magnifying glasses and all sorts of other focus aids. As long as you are focusing on the frosted side of the ground glass, as sharp as it gets with the loupe is the correct focus. My current favorite "loupe" these days is a small pull-out 8x magnifying glass with one aspheric element (exactly the one that Sherlock Holmes uses in the "Sherlock" series). It has no skirt; I just hold it the right distance from the gg.

    There is a problem if you focus on the image in a different place than on the frosted side of the ground glass. This would seem to me only possible with the aerial image, but I'm not sure.

    Quote Originally Posted by LotusEsp View Post
    ... I did another loupe test last night, and found that I was looking at the ground side (closest to the lens) of the GG, not the smooth side. There are black lines etched into the ground side and these focus up with the grain. ...
    This is exactly correct, so it's likely not your loupe or your focusing that's the problem.

    Best,

    Doremus

  9. #19
    Jim Jones's Avatar
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    Re: 4 x 5 focus problem

    Quote Originally Posted by LotusEsp View Post
    thanks Jac
    are there any walk through of aerial focusing? I've been searching but can only find vague referencing to the process, drilling holes, using thin wire etc. Nothing comprehensive
    My first choice would be to polish out the ground glass texture in a small spot for aerial focusing rather than drill a hole, although I've never had to use aerial focusing.

  10. #20

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    Re: 4 x 5 focus problem

    Quote Originally Posted by LotusEsp View Post
    any suggestions on a good loupe?
    Peak brand, Schneider...

    I like this one I like:

    http://www.bhphotovideo.com/c/produc...oom_Loupe.html

    but I'd prefer to buy 20 8x10 Velvia sheets : )


    I use this one, same of the above link, but AP branded... http://www.bhphotovideo.com/c/produc...yle_Loupe.html

    It is said that 4x is better, but for me 8x also works perfect, well you see less area and ground glass grain is perceived to much, but I check focus perfectly.

    Just one thing, if one needs glasses to read, and most of 40+ years old people do, then one needs something that can be adjusted, same like the diopter of DSLRs...

    ...I have to rise the AP loupe some 4mm from ground glass to sharpen the image, this can be confusing, I've to add an spacer to adjust the loupe to my eye !!

    I made the barrel near opaque with a permanent marker. Yes... a good loupe is a great thing if one shots a lot !!!

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