Page 1 of 3 123 LastLast
Results 1 to 10 of 27

Thread: Testing ground glass register

  1. #1

    Join Date
    Jul 2013
    Location
    Queensland, Australia
    Posts
    473

    Testing ground glass register

    I have a Shen Hao 4x5, which I have not used for a while, I bought a Maxwell screen for it due to a really dim image on the gg. I can't praise this screen enough, but suddenly I was getting soft slightly OOF images? It was retired for a time. I recently took it for a three hour trip down to the coast to shoot some long exposures of the coast, old boats, piers and the like. I returned home excited to develop these pics, only to find them all soft, thinking it was my sironar 210mm lens I set the tripod up in my little studio and tried to focus on the following image, well the smallest writing on the paper, which was the internet address. It focused fine, so it wasn't the lens, which only left the registry. After countless exposures I finally got a decent picture with two slices of film and two strips of thin paper on each side of the GG to push the GG back to the film registry. Pics are now sharp.
    So I got out my 8x10 which has never had a film through it, to test my new-to-me fujinon w 250mm f6.7 (arrived today), once again I have the soft image problem, back to the studio, and the lens actually produces a sharper image than the sironar. Rather than spending lots of film doing the same registry alignment test, I thought I might ask the more experienced if there is an easier way?? I don't mind zeroing this way, but if there is another method I would be interested to here about it.
    Click image for larger version. 

Name:	registry test.jpg 
Views:	89 
Size:	37.4 KB 
ID:	180316

  2. #2

    Join Date
    Feb 2008
    Location
    The Highlands of Scotland
    Posts
    344

    Re: camera registry

    There is an ISO standard measurement for the distances between the depth of the film holder front edge and actual film plane.

    This should tie up with the location of the ground glass surface in the focussing screen.

    I'm not sure if the measurements are the same between 5x4 and 10x8......but I'm sure someone who does know will be along soon to explain in detail :-)

    Mike

  3. #3
    Jim Jones's Avatar
    Join Date
    Aug 2006
    Location
    Chillicothe Missouri USA
    Posts
    3,065

    Re: camera registry

    The standards Mike mentioned has been discussed at length here: http://www.largeformatphotography.in...der+dimensions.

  4. #4
    Tin Can's Avatar
    Join Date
    Dec 2011
    Posts
    22,387

    Re: camera registry

    Wood camera, maybe it dried out and shrunk a bit.

    Your shims seem to be only 0.010". The spec is 0.014" wide or +- 0.007".

    I can think of other variables, but that's for others to introduce.

  5. #5

    Join Date
    Sep 1998
    Location
    Oregon now (formerly Austria)
    Posts
    3,397

    Re: camera registry

    I take a photo of a detailed horizon line (e.g., hill with tall trees) at infinity focus and a wide aperture every now and then to check my ground-glass alignment. If it's off, then a test with a ruler at an oblique angle to the camera is done. Shoot at a wide aperture and focus on a specific marking on the ruler. If the focus is off one way or the other, then you at least know which way you have to move the ground glass. Shim a bit and test. When I need to re-adjust the ground glass, I do the tests when I'm set up for printing. Shoot the neg, 3 minutes in Dektol, stop and fix, rinse and inspect wet with the magnifier. Re-shim and repeat as needed.

    I have a good depth micrometer too, but find the practical tests to really be the fine tuning I need.

    Best,

    Doremus

  6. #6
    Drew Wiley
    Join Date
    Sep 2008
    Location
    SF Bay area, CA
    Posts
    18,338

    Re: Testing ground glass register

    You're wasting your time unless you have a precision vacuum or adhesive film holder, because your film is not otherwise laying flat. Ordinary holders do not do that. At a minimum get some thin removable double-faced Scotch tape to tack down the center of the film where it bows the most. As an option you could try viewing the aerial image using a good loupe with no film involved. But fresnels or screen intensifiers make this second approach quite difficult, because they might be part of the problem. Ordinary holders cannot do that, especially with large sizes of sheet film. Filmholders as well as camera backs can also become warped or misaligned. You have to check every variable step by step in a process of elimination. Besides a truly trustworthy film holder, get a straightedge which is precisely ground flat - not some mere aluminum extrusion or cheap level.

  7. #7
    ic-racer's Avatar
    Join Date
    Feb 2007
    Posts
    6,737

    Re: Testing ground glass register

    You only need one full sheet of film. Exposing film in the film holder is the only way to really know what is going on. When you determine how far off your negative image is from the target you can use the simple lens equation to estimate the GG correction needed:
    1/(intended target distance mm) + 1/(intended film plane mm) = 1/(focal length mm)
    1/(actual focus distance mm) + 1/(actual focal plane mm) = 1/(focal length mm)

    Solve for "intended film plane" and "actual focal plane" and subtract them to estimate the ground glass error.

    You can wrap ten turns of tape around a rod and measure the thickness divided by 10 to find out the thickness of your 'shim' tape, if needed.

    For example with your 210mm lens, if you focus at 2 meters and the processed film image is sharp at 1.9 meters your ground glass is 1.5 mm too close to the lens.
    If you wrap ten turns of tape around a pencil and measure it to be 4mm then you could use 3 or 4 layers of that tape to shim the ground glass back.

    If you wonder if you could just "stop down" take note that f16 gives 1mm of depth at the film plane and f22 gives 2mm.

  8. #8
    Randy's Avatar
    Join Date
    Dec 2010
    Location
    Virginia, USA
    Posts
    1,486

    Re: Testing ground glass register

    Brrrr - all this talk sent a cold chill down my back - I am almost done building an 8.5 X 15" back (including a slide-in ground-glass frame with home-made gg) for my 8X10 camera so that I can use a Vageeswari film holder I purchased. I wonder if there is any chance that I'll get lucky
    https://dl.dropboxusercontent.com/u/52893762/bigger4b.jpg

  9. #9
    Drew Wiley
    Join Date
    Sep 2008
    Location
    SF Bay area, CA
    Posts
    18,338

    Re: Testing ground glass register

    I have a long bar of Starrett precision-ground flat stock with a hole drilled in the middle to accept a digital depth micrometer. I have yet to encounter a view
    camera where the film plane is entirely correct; and I've got some Swiss Sinar Norma, F, and P gear. So don't expect any wooden camera to be precise and
    without need of a bit of tweaking. But in most cases you should be able to achieve "precise enough". Certain old roll film holders and warped sheet film holders are hopeless unless being somewhat out-of-focus is just part of your game; but in those cases, expect light leaks too.

  10. #10

    Join Date
    Jul 2006
    Location
    Collinsville, CT USA
    Posts
    2,330

    Re: Testing ground glass register

    Adding in my 2 cents... Orientation of the camera is important. Years ago was using an 8x10 Sinar Norma, mounted on a Linhoh Heavy Duty Copy Stand, above my Nikon SKe microscope to take some photomicrographs. Focusing was tricky (couldn't reach the focusing knob on the microscope where at the same time viewing the GG). First few negatives turned out to be out of focus. Figured that because the film back was horizontally (pointed face down), the sheet of 8x10 film had to be sagging a few mm's. Configuring an adhesive back to the film holder surely would have worked, but never thought of that at the time. So I exposed 5 sheets of film lowering the back 1mm at a time. Turned out that lowering the back 4mm solved the problem (compensated for the sagging of the film) in the center of the image. In the end lowered the back 3mm to get the best overall focus across the negative which worked out just great for contact printing the negatives.

Similar Threads

  1. Good ground glass vs. bad ground glass
    By BarryS in forum Cameras & Camera Accessories
    Replies: 4
    Last Post: 22-Aug-2017, 03:29
  2. How to register film boundary on ground glass
    By Tom Westbrook in forum Cameras & Camera Accessories
    Replies: 8
    Last Post: 18-Feb-2007, 06:17
  3. Testing for Correct Position of Ground Glass
    By Brian Ellis in forum Cameras & Camera Accessories
    Replies: 19
    Last Post: 17-Feb-2005, 15:39

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •