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Thread: Focus Problem with GG?

  1. #1

    Join Date
    Jul 2017
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    Question Focus Problem with GG?

    I'm not new to 4x5, but I have recently acquired my first Anniversary Speed Graphic. I am having problems getting my image in focus. I have no problem getting the image in focus on the ground glass, but on my fp100c image the focal plane had shifted to the foreground. I double checked that the focus didnt change as i was switching out my back, and it did not move.

    I'm using a fuji PA145 back
    ground glass has no fresnel or shims.
    ground glass has frosted side toward lens
    camera is mounted on a solid tripod that doesn't move (image is still sharp, just moved to foreground)

    Any suggestions?

  2. #2

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    Re: Focus Problem with GG?

    Sounds like your ground glass is in the wrong plane, relative to the film plane.

    Get hold of (or make) a focus checker. It's a series of thin lines drawn at regular (say 5mm) intervals, either side of the centre line on a sheet of card.

    Place it at 45į to the film plane, focus on the centre line, expose and process the film. Once the film is dry, you can check to see which line is sharp and how far out the actual focus is, then shim the GG accordingly.

    Mike

  3. #3

    Re: Focus Problem with GG?

    Or you can use a depth probe micrometer and take the guessing out of the equation. Very easy iteration for a small film size as 4x5. If you do not have the equipment nor desire to deal with this issue, send your GG back to a competent large format person like Richard Ritter and let them get properly on the proper film/GG plane alignment.
    Last edited by Michael Kadillak; 22-Oct-2017 at 20:19. Reason: typo

  4. #4

    Re: Focus Problem with GG?

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    Everything you need is illustrated. Compare the depth of a sheet of film in your holder to the depth of the ground glass in the camera's back. Use thin plastic or brass shims (available in decimal sizes in the Model Railroad department of Hobby Shop) to shim your ground glass to match the depth of the film.

    Of course if you have a fresnel then all bets are off and you're back to trial and error, shooting multiple sheets of film at different depths to zero in on the correct position. If you shoot one test then add shims and shoot another, then process the two sheets (put an identifier in the shot) you can narrow it down quicker but it will still take several iterations.

  5. #5

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    Re: Focus Problem with GG?

    Very first thing you should do is shoot a sheet of film, or 2, in a standard sheet film back to make sure that your problem isnít where the film lies in your Fuji holder,

  6. #6

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    Re: Focus Problem with GG?

    As Bob says. But isn't the graphic old enough to use the 5.08mm offset rather than the current 4.8mm? See this thread: http://www.largeformatphotography.in...lass-plane-MPP

    If so, you need to shim in the wrong direction, i.e. move the film nearer the lens. I'm currently designing/building a new glass holder for my MPP (rather than machining the existing holder; that's a tricky job and I don't want to wreck it).

    Neil

  7. #7
    gimenosaiz's Avatar
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    Re: Focus Problem with GG?

    Quote Originally Posted by Monza1966 View Post
    I'm not new to 4x5, but I have recently acquired my first Anniversary Speed Graphic. I am having problems getting my image in focus. I have no problem getting the image in focus on the ground glass, but on my fp100c image the focal plane had shifted to the foreground. I double checked that the focus didnt change as i was switching out my back, and it did not move.

    I'm using a fuji PA145 back
    ground glass has no fresnel or shims.
    ground glass has frosted side toward lens
    camera is mounted on a solid tripod that doesn't move (image is still sharp, just moved to foreground)

    Any suggestions?
    Hello!

    I'd that problem with my Pacemaker Speedgraphic.

    In my case, I've fresnel+GG and the solution was to turn the GG. It was wrongly placed.

    Cheers
    Antonio

  8. #8
    Jim Jones's Avatar
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    Re: Focus Problem with GG?

    Perhaps the best standard to which adjust the ground glass distance to the back of the camera is to adjust it to a nearly universal standard rather than to one's film holder. The "T" distance (from the face of a 4x5 film holder to the back of the film slot) is 5mm +/- 0.178mm or o.197" +/- 0.007". This information comes from a 1998 publication of ANSI/PIMA IT3.108-1998.

  9. #9

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    Re: Focus Problem with GG?

    That may be the standard, Jim, but every one of my Fidelity 4x5 holders is 4.8mm +/- 0.01mm from the reference plane.

    Neil

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