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Thread: ground glass film plane

  1. #1

    ground glass film plane

    I've just begun to use my grandfathers wooden 4x5/5x7 view camera (KODAK). I've noticed that even thought the image on the ground glass seems to be tac sharp the negatives are slightly soft. I do not believe this is the original ground glass and was wondering if the alignment is off and how do I check it? I would also like to replace the ground glass with a newer and brighter one, any suggestions? Is this something I can do myself or is it something that needs to be adjusted by a professional?

    kenn

  2. #2

    Re: ground glass film plane

    Kenn
    it's easy to do .the ground surface of the glass should be 4.8mm from the frount of the frame, thats the one that faces the lens,

    To grind your own glass you need a piece of glass the size and thickness you want to make, and another sheet of glass a bit larger, then you need some Silicon Carbide grit I use 220 grit, use the stuff that people polish stones with, not the stuff for car engines, a little water, a teaspoon of grit, and one off water grind together and in about 20mins you have ground glass,

    bob

  3. #3

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    Re: ground glass film plane

    Bob:

    In re: GG grinding.

    Is there any special way to do that grinding?

    Something like so many minutes front to rear, then so many minutes left to right? Or, grind in a circular pattern? Big circles or little circles? How much pressure to apply?
    Do you replenish the silicon carbide after so many minutes of grinding has worn it down? Etc?

    I have thought about trying to grind my own glass, but don't know anything about the best procedures to use when doing the job.

    Eu

  4. #4

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    Re: ground glass film plane

    EuGene,

    Put a dolop of the carbide on the glass and a little water, enough to make into a thick paste, and work in a circular motion, you will know if you have to add more water or carbide as it will either start to stick, or it will stop feeling like it is grinding, I don't use carbide, but the principal is basically the same with the material I use, another little tidbit that will help, is add 1 drop of liquid dish soap, this will float the grinding material a bit better and create less resistance. Make sure to get the best quality glass you can, cheap glass, often times, when it cools will have dips and valleys in it which makes it more difficult to grind. I normally suggest grinding a 4x5 size on an 8x10 and recommend about 15lbs of pressure, make sure your glass is clean and there are no little shards on the edges from the cutting procedure, if there is, they will cause deep scratches that are very difficult to remove...

    Good Luck.

    Dave Parker
    Satin Snow Ground Glass

  5. #5

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    Re: ground glass film plane

    Check to be sure the ground surface of the glass is facing the lens. If not, this would be a major factor in the focus being off.

  6. #6

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    Re: ground glass film plane

    Thanks, folks.

  7. #7
    Richard K. Richard K.'s Avatar
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    Re: ground glass film plane

    Quote Originally Posted by Kenn Gallisdorfer View Post
    I've just begun to use my grandfathers wooden 4x5/5x7 view camera (KODAK). I've noticed that even thought the image on the ground glass seems to be tac sharp the negatives are slightly soft. I do not believe this is the original ground glass and was wondering if the alignment is off and how do I check it? I would also like to replace the ground glass with a newer and brighter one, any suggestions? Is this something I can do myself or is it something that needs to be adjusted by a professional?

    kenn
    As long as it isn't reversed (ground side away from lens), it's installed fine and doesn't have to be original. Are your holders compatible? Are they modern? Original? Converted glass plate? These could all have different "T" distances (distance from septum to top edge of holder) or assume a thick glass plate is being used rather than a thin (7 mil?) film and could easily account for what you are seeing. This problem can also occur when supplying different brand or newer holders to an older camera , say a Folmer & Schwing...

  8. #8
    lenser's Avatar
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    Re: ground glass film plane

    Another thing to check is the corners of the ground glass related to the wooden frame. In many old wooden cameras, the corners of the GG must be trimmed in order to seat properly. I've encountered some ground glass backs where the inset corners of the frame is actually beveled up to the top edge to ensure this. If your GG is a replacement, and some previous owner didn't understand this, it could be untrimmed and therefore riding on the tops of these bevels.

    The purpose of the bevels is to ensure that the corners were trimmed so the photographer could look into each open corner to see if part of the lens glass was visible, thus being sure that his or her lens was covering the entire image area.

    Remote those this possibility is, I've seen dumber things happen and that would make it certain that your focus would be off even when stopped way down.

    Tim
    "One of the greatest necessities in America is to discover creative solitude." Carl Sandburg

  9. #9
    Robert A. Zeichner's Avatar
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    Re: ground glass film plane

    The first thing you might check is to see if this camera was designed for use with plates or film. I had a Century Grand Sr. that was designed for plates and I needed to fabricate a shim to place between the back and the gg while focusing to compensate for the depth difference in a film holder. The distance from the gg to the front surface of the back is inconsequential. The important dimension is between the ground surface of the glass and the surface against which the film holder rests when inserted in the camera. The plane at which the film emulsion sits when the holder is inserted needs to be coincident with the plane of the ground surface of the gg when the holder is removed.

  10. #10

    Re: ground glass film plane

    Thanks for the great ideas. I am using modern film holders. The ground glass is thin and beveled in the corners. I'm thinking that all of this is a little beyond me and I should have the camera checked by a professional in this area.

    If I just wanted to purchase a new ground glass, one that was very bright, dose any one have any suggestions?

    kenn

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