Checking folder lens zone focus w/ GG

Discussion in 'Medium Format Cameras and Accessories' started by Murray@uptowngallery, Jun 20, 2005.

  1. Murray@uptowngallery

    Murray@uptowngallery Member

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    This is driving me nuts.

    I have several cameras with zone focus and I am trying to check focus on them by putting ground side of a piece of ground glass against the film plane. Only one has a stepped plane, apparently one level for film and the other for paper backer. On that camera the GG went against the smaller, 'furthest in' plane, closest to the lens. It seemed apparent that was where the film would lie. I hold the GG flat with a wide rubber band.

    Taking the outer cell off to clean it, I learned ther are apparently 3 starting threads, I assume roughly or perhaps necessarily 120 degrees apart. Not only are they frustrating to restart, I can't find any distance yet that makes ANY sense at all. With the infinity 'stop' pin removed to allow removal of the outer cell, I noted that I don't really know how many cell turns in infinity should be at...if it's possible to go one turn too far, or if screwed all the way in is infinity. If I start the thread that aligns with the infinity mark (a good sign), it threads in 2 or (I forget at the moment) 3 full turns. But focussing near or far doesn't give a distance that makes any sense. If it were WAY off, I wouldn't have expected on of the lens threads to start right at the infinity mark (?!?)

    I'm disturbed (more than normal) by all three cameras I've tried doing this with, so I wonder if it's me (my eyes are bugged out too far from stress?).

    Maybe I'll try this with a working SLR to make sure it isn't operator error.

    I personally need a loupe to check this, but don't think the actual position of the loupe should affect the focal point, just the degree of enlargement and distortion and be fumbly to hold at the same time as rotating the lens cell. At least I put the camera on a tripod.

    Any clarification available?

    Thanks
     
  2. phfitz

    phfitz Member

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    Murray,

    On all of the front-focus folders I have played with, the 'beauty ring - focus scale' is held onto the front cell with 3 set screws so it can be repositioned. They are tiny, use your loupe to find them. It may be easier to sharp focus at 25 feet and set the scale to that then check for inf.

    It is easier to set the lens to inf., remove the ring and count how much of a turn to move the cell all the way in. Clean it and replace it all the way in and turn it out that far.

    Good luck with it.
     
  3. Murray@uptowngallery

    Murray@uptowngallery Member

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    Really tiny screws on the one I'm working on.

    So which thread is started doesn't affect cell spacing?
     
  4. skahde

    skahde Member

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    Make your own collimator. Take a long hair and tape it straight on the film rails and over the film plane. Then take an slr with a split-image rangefinder and focus it to infinity (better use a very distant object than trusting the scale, using moderate tele-lenses is easier and more precise than wide-angles). Position both cameras facing each other lens to lens. Look through the viewfinder of the slr and adjust focus on the folder untill the hair is no longer split. Now carefully set the folders focus-ring which you have loosened beforehand to infinity and fix it in this position. I did this with an Agfa Record II some month ago and was quite surprised by its nice performance.
     
  5. medform-norm

    medform-norm Member

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    Murray, are you sure that in your stress/panic you may not have put back the front cell the right way round? Perhaps you need to reverse the lens element.
    That could give funny results too.
    Good luck, norm
     
  6. Murray@uptowngallery

    Murray@uptowngallery Member

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    skahde, collimator sounds interesting. With SLR at infinity, how close together need the two cameras be.

    m-Norm, front cell glass is captive in the 'barrel'. Only option is the three different starting threads.

    Back to it again. Thanks both of you.
     
  7. Murray@uptowngallery

    Murray@uptowngallery Member

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    Say, I did make an 'x' in pencil on the ground side of the ground glass for some future use. I also wanted to try the oil spot technique in center of the GG.

    Will that 'X' and sufficient backlight serve instead of a hair? I had been leery of keeping a hair flat when reading of this technique previously. I wasn't too impressed with 'Scotch Magic' tape flatness prior to cutting ground glass.
     
  8. medform-norm

    medform-norm Member

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    We always make pencil marks on GG's - no scotch tape needed and easy to remove later. Plus flatness garanteed.

    If only option is three starting points I can only suggest keep trying, as I haven't seen the camera you're talking about. Pics always help (hint).
     
  9. skahde

    skahde Member

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    The exact distance doesn't matter. Just place them as close as is convenient. Keeping a hair flat is easier than one might think. A hair is quite flexible at a length of several centimeters and putting it their with some tension is easily done with adhesive tape.
     
  10. Claire Senft

    Claire Senft Member

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    Is it possible that photographers living in Holland Michigan that take apart devices with which they are unfamilar can soon find themselves in "dutch".

    Have you managed to put that watch back together correctly that you took apart as a kid? I would have thought you would have learned then what Clint Eastwood has been trying to tell people "A man has got to learn his limitations".

    Good luck with your project.
     
  11. John Koehrer

    John Koehrer Subscriber

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    Murray,
    Patience is the key. The home made collimater will work but so does the ground glass. Your primary aim is for infinity & all else will fall into place.
    If you get frustrated enough let me know & you can send it to me & I'll set it up for you. One of my earlier incarnations was as a camera technician. If you need a rec talk to Joeyk49. All it'll cost is shipping & a donation to APUG. $$ is up to you.
     
  12. Donald Qualls

    Donald Qualls Member

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    I've never used a collimator, only a piece of stiff plastic with frosted tape on the lens side. It's cut to the dimension of a 6x9 negative, plus a little on the length, so I can be sure it will sit in the proper place (and BTW, the film and paper are so close to the same width, a stepped plane can't be for film in the lower and paper in the upper; rather, it's to keep the pressure plate from making scratches in the film by insuring a fixed amount of space). I use a loupe (or the back element from a triplet) to examine the image and establish critical focus on an object *at least* a quarter mile away, preferably a mile or more.

    The cameras I've reset this way have produced some of the best images I have (including my Wirgin Auta, Kodak Reflex II, and Argoflex EF).

    The ring vs. lens barrel varies from camera to camera. My Wirgin has four starts, and only ONE of them will allow setting the focus correctly and mounting the name and focus scale correctly as well. What I found worked well with this camera was to set the focus, test the fit of the rings, and if it wasn't right, back the front element off carefully, while pushing it *on*, until it "clicked", then screwing it back in, and going again. This allowed me to proceed sequentially around each of the four starts until I found the one that allowed the correct scale and name ring installation with the focus correct.

    Other cameras are easier on this; the Reflex II and Argoflex both have "infinitely adjustable" settings, so it doesn't matter which start you get the lens on when reassembling.
     
  13. Murray@uptowngallery

    Murray@uptowngallery Member

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    :O)

    Limitations? I haven't choked on any of the parts yet, and this is a better habit than heroin, so I'll keep going.

    Is Claire's location really Nilwaukee (tongue-in-cheek spelling), or is that a typo (sorry, I used to work for a newspaper)?
     
  14. Murray@uptowngallery

    Murray@uptowngallery Member

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    OK, I read the rest of the posts. Good info and humor. I will go at it again more methodically, and look for how many thread starts there are.

    There were no clouds yesterday, as that is what I hoped to focus on. Instead I just compared to separate rangefinder since I was trying to get from 'rediculously far off' to 'close'.

    Thanks

    Murray
     
  15. John Koehrer

    John Koehrer Subscriber

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    Murray,
    You don't need clouds in the distance to set focus. They don't stand still long enough & don't have sharp edges. Youu should have a target 500-1000 times the focal length of he lens. I typically use a tree top about a block away as a target although a building with brick work or decoration would work well also. Any fine detail is good.
     
  16. Claire Senft

    Claire Senft Member

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    Nilwaukee is a state of mind located within the confines of Milwaukee. I am finding myself having to do more and more with less and less. This would be more tolerable had I not started with so little in both resources and talent. As soon as I figure out how to create matter I am going to have on hell of a good day down at the patent office. Do not look for this to happen anytime soon.
     
  17. Murray@uptowngallery

    Murray@uptowngallery Member

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    :O)

    USPTO and freepatentsonline are my friends, well, aquaintenances, anyway.
     
  18. Murray@uptowngallery

    Murray@uptowngallery Member

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    500-1000 x f.l., ok... I have too many trees obstructing my view but I have tried to do this...best I can do. The fraction of a mile seemed too far away, but I have no idea how far my targets really are...I'll just make do with the furthest thing that isn't moving....

    Murray