Accurate 4X5 film holders - measurementsgreenspun.com : LUSENET : Large format photography : One Thread
I've heard some talk on this board about the accuracy of film holders and I am talking to a tool and die maker about making a device to more conveniently measure the film holder outer flange/back, film plane area of the holders. Does anyone know, for sure,what this distance it?....and is the ANSI spec sheet...#ANSI/PIMA IT3.108-1998? Thanks in advance for any help. Richard Boulware - Denver.
-- Richard Boulware (firstname.lastname@example.org), June 20, 2001
Z38.1.51-1951 is the ASA standard for Photographic double film holders of the lock-rib type. Nominal depth is .197" +/- 0.007" for 4x5 size. I hope this helps and would be curious to hear about what you come up with.
-- Robert A. Zeichner (email@example.com), June 20, 2001.
Richard: It really does not matter what the number is, what counts is that the distance from the rim of the holder to the film be exactly the same as the distance from the rim of the groundglass frame to the ground surface of the glass. In that way the film will be on the same plane as the ground surface of the glass. Yes there are standards, an ANSI and a DIN standard. There is small difference between the standards, not large but significant in that the difference is as large as camera manufacturers like Sinar allow in the design of their holders for film buckling, i.e. 0.0005". About the device for measuring the film holders, all that is required is a simple FLAT machined aluminum plate with 15 holes spread evenly throught the plate and a depth micrometer. Be careful, doing it accurately requires lots of practice and statistics to determine the accuracy and reliability of your measurements. Make sure your micrometer is zeroed against flat plate glass. Micrometers tend to deflect the septums unless you use extreme care. It is difficult to feel the point at which contact is established so I had to rely on my ears to give me additional feedback. I found measuring polaroid backs and grafmatic holders next to impossible because of the very small force needed to deflect them. Non contact (laser) measurements are far more reliable but beyond reach for photographers. The most accurate holder I measured was a Linhof, with about + or - 0.0005" deviation from flatness, although there was a difference in the depth from one side to the other of about 0.003". This was a very old holder. Mitutoyo makes excellent micrometers. Their digital ones are my preference although I use an analogue which is cheaper. Good luck!
-- Julio Fernandez (firstname.lastname@example.org), June 21, 2001.
This question keeps cropping up, and coming to no dfinite conclusion. I've done a bit more research since the subject last appeared, and there seems to be no agreement between camera makers over what the GG register should be. A mini-survey in 2000, by a contributer to the British Journal of Photography found 5x4 camera-back to GG distances varying between 4.67 and 5.05 mm. They can't all be right, now can they? This sort of sloppiness just wouldn't be tolerated in smaller formats, so why should we throw away precision just because our film area is a bit bigger?
The ANSI/ISO standard for film holders is a depth of 5mm (0.197") from mating-face to septum, that seems clear, but the septum is where the back of the film rests, if you're lucky. This means that the film emulsion is at least 0.2mm higher than this. That's with a 'standard' film base thickness of 0.18mm plus the emulsion thickness. (This seems pretty consistent. I've put a micrometer to several different makes and types of film; they're all 0.2mm thick within a very small tolerance.)
The conclusion to be drawn is that the GG ought to be at a distance of 4.8mm from the mating face of the camera back. This also tallies pretty closely with the older ANSI standard set down for plateholders of 3/16", or 4.76 mm from the film surface to the camera back. I've been unable to find an ANSI/ISO standard for a cut-film register.
Accepting 3/16" or 4.76mm as the defacto standard would seem to be the logical thing to do. It's only .04 mm (1.5 thou) away from the minimum average distance of a cut-film emulsion, in an holder that meets the ANSI/ISO standard, and any film bowing will always mean that the film will be slightly closer.
It seems ridiculous that standards authorities don't seem able to set this distance down for camera makers to adhere to. I personally think it's about time there was a grass roots movement to fix on a standard, before LF disappears for good.
-- Pete Andrews (email@example.com), June 21, 2001.
Richard, There is a simple little tool that your toolmaker friend shouldn't have any trouble with. It can best be described as a wedge, made from aluminum, about two inches long, .250 in. wide, and maybe .160 thick on one end and .240 on the other. You mark the thickness in .010 increments and interpolate readings in between. All you do is set the wedge on the septum and drag a sgraight edge across the mating surface until it hits the wedge, then read the thickness. It's light enough so that you don't have to worry about deflection. I made one for 8x10 a few years ago and proceeded to loose it, otherwise I would send you a JPG. This also works in checking your ground glass.
-- Bruce Wehman (firstname.lastname@example.org), June 21, 2001.