Checking folder lens zone focus w/ GG
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?
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.
Really tiny screws on the one I'm working on.
So which thread is started doesn't affect cell spacing?
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.
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
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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.
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.
We always make pencil marks on GG's - no scotch tape needed and easy to remove later. Plus flatness garanteed.
Originally Posted by Murray@uptowngallery
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).
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.
Originally Posted by Murray@uptowngallery
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.