Re: [Cameramakers] Re: Film holder/gr glass measurements
Thanks --Michael [EMAIL PROTECTED] for the up-to-date data. My source is ancient and lacks tolerances (I think!) However, I question one detail below: The ANSI standard for the depth of a standard 4 x 5 inch film holder is 0.197 plus minus 0.007. Most film has a base of 0.007 . When film is loaded in the film holder, the depth is 0.190. This is the measurement used by Sinar cameras. Wisner cameras use a compromise of 0.192 to allow for wear on the wood and because Tech Pan film, used by some photographers to achieve ultra-sharp images, has a base of 0.004. ### I infer from this that you must add a correction depending on the thickness of the film base but I believe this is wrong, at least for the film holders I know. The location of the film plane is set by a narrow ridge around the edge of the film. The film is pressed forward against this fixed ridge by a movable pressure plate until it contacts the fixed rige. It is the emulsion which is then at the location of the ridge surface and the location will be independent of the base thickness. You might consider a correction for emulsion thickness but that will be far below the tolerance band except for some unusual film, and even with such a film I might select forming a sharp image at the surface, where diffusion in the emulsion has not yet taken its toll. The only time one should even begin considering the base thickness is with a film lacking an anti-halation backing or tinted base, both of which surpress reflections from the back of the film. Or, one other special case, the vacuum back. Here it depends on how the film is located. If the film still presses against that ridge and the vacuum back floats to conform to the ridge location, nothing will be changed. In the big repro cameras I have seen in use, the back is fixed and arbitrary size film is sucked against the plate. The location of the back does not change to accomodate the film thickness and here a correction will be needed. As for the tolerance band, I would try to stay closer to the 0.190; if my back-of-the-envelope calculation (based on simple geometrical considerations) an error of 0.007 inch will degrade the resolution considerably at F4, and if you are lucky enough to have an F2.8 lens for 4x5 (Aero Ektar or Schneider Xenon, at 2.8) and wish to photograph at full aperture, you will be reaching much less than the capabilities of the lens (50 lp/mm or better, and with the Aero Ektar, I believe well over 100 lp/mm, so the film is limiting if you focus well, which you can hardly do with sloppy 0.00 inch errors!) Bob Bob ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
[Cameramakers] RE: Filmholder measurements
On 17-Aug-02 [EMAIL PROTECTED] wrote: The ANSI standard for 5 x 7 and 8 x 10 inch film holders are as follows (film thickness has not been deducted): 5 x 7 0.228 + - 0.010 8 x 10 0.260 + - 0.016 These measurements may be checked with a Vernier calliper gauge or a micrometer (available in some hardware stores). Vernier callipers take measurements to 0.1 mm or less. [End of quoted segment] I don't know what the dimensions might be for 11x14 and larger cameras. This of course, then, would depend on what film holders you're using. My understanding is that there is no ANSI standard for filmholders larger than 8x10. For 11x14, the dimensions of the Fidelity/Lisco holders must be the de facto standard. I have heard that 11x14 holder for X-ray film are different. For larger cameras, there is no standard -- different manufacturers used different registers (depth of film in the holder). This is a problem for people with banquet cameras who wish to buy a used holder. My advice if you are planning to make a LF camera and buy holders: buy one holder at the beginning to get all relevant dimensions and test fit as you make the back. If you are planning to make the holders, then make one first, then make the camera to match. One reason is that if you decide the holder is too hard to make, you can switch to buying commercial holders before making the camera. If you want the holders that you are making to match the dimensions of commercial holders, it might be best to buy one as a sample. If you don't want to spend the money for a very larger holder and want to make one to the dimensions currently used by camera manufacturers (Canham, Lotus, Wisner, ...), perhaps one of them would tell or sell you the information if asked nicely. Or perhaps you could advertise on one of the LF lists, asking to borrow a holder via making a deposit, and measure it. --Michael --Michael ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
[Cameramakers] Re: Film Holder Measurements
Hi again, Boy, I think -- well, sometimes I think (bad joke) -- ahem, I seem to recall that eons ago there might have been some info somewhere on the Web about this, and I think it might have come into the Cameramakers List at one time. Might be worth a peruse of the archives. Unfortunately, I am at the moment trying to unclog a drain in my kitchen (waiting for the Liquid Plumr to work) and need to handle a backlog of chores (which I have cheerfully neglected recently) so I can't dedicate the time to perusing this myself ... but will in the next few days given the opportunity (time). Meanwhile, if someone out there has the moments to spare -- I've found in the past that downloading the archive and then doing a search in a word processor works fairly well. Meanwhile also I'll see if I can find my notes of about a year ago or so; I know I have a notebook around here somewhere with some data 'Bye for now, --Michael [EMAIL PROTECTED] ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
Re: [Cameramakers] Filmholder pressure plate question and aerial camera tolerance
The pressure plate film holders are a special hard to find item. I have only seen them twice on E-bay in 8x10 size.. I had mentioned it because it would be a light weight alternative to a vacuumed back keeping the film very flat which would be important when dealing with such large film... ... - Original Message - From: Uptown Gallery [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Sunday, August 18, 2002 7:17 PM Subject: [Cameramakers] Filmholder pressure plate question and aerial camera tolerance I must be missing something. I have some film holders but haven't used them yet (no camera yet!). I don't see a moveable/adjustable pressure plate. I see a hinged access part that opens after removal of the darkslide, then metal guides that the film slides into, and a depression for a thumbnail to extract the film. There are little levers that rotate to 'lock' the darkslide in place. I'm told they also serve a purpose for keeping mental note of which side of the film holder has been exposed. Do they serve a second (third?) function of applying pressure on the film? I thought the film holder basically just holds the film from curling up, and with very large format, the film can bow away from the back of the film holder. From what I've read, apparently some early aerial cameras did not have vacuum to hold the film, and the film did lift away from the platen (back of their film holder). A guy told me that they would then only shoot during a declines to 'push' the film flat against the platen, and that was why vacuum was added...so they could shoot at any inclination. Another guy gave me an interesting explanation from his father who flew a plane with a camera, about the nighttime cameras with the f/2.5 Aero-Ektar lens and 'flash bombs'. They dropped a 50 pound flash bomb containing 25 pounds of flash powder, set to ignite at various altitudes. The camera had a photocell of sorts to detect the flash and trigger the shutter. The flashbomb was on the order of 2 million candlepower. Having no practical perspective for this, I inquired if this was noticeable to the subjects being photographed. He said it sure as %@#%^ did - it illuminated the ground to mid-day brightness - they'd shoot maybe 6 shots (on a 3 second or so cycle) and scramble out of there as fast as they could. A former-photographer neighbor has a 16 x 20 camera in storage - I'm thinking of asking him if I can take measurements on the film holder, but I will have to rely on a tape measure for the height and width - I don't have a caliper that huge. Murray ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
Re: [Cameramakers] Filmholder pressure plate question and aerial camera tolerance
At 2002/8/18 19:17:00, you wrote: There are little levers that rotate to 'lock' the darkslide in place. I'm told they also serve a purpose for keeping mental note of which side of the film holder has been exposed. Do they serve a second (third?) function of applying pressure on the film? ^^ Nope. Their purpose was to hold the darkslide in place when the holder was being handled, especially when picking it out of the case. The way to indicate that a film was exposed was to turn the darkslide over (while the holder was in the camera, of course.). The metal grip at the outer end of the slide had notches or embossed dots which could be felt in the dark, and one side of the metal outer end was painted black. The bright side indicated the film was unexposed; the black indicated the converse. (I had a boss once who insisted on reversing this convention. Talk about potential problems.) I thought the film holder basically just holds the film from curling up, and with very large format, the film can bow away from the back of the film holder. From what I've read, apparently some early aerial cameras did not have vacuum to hold the film, and the film did lift away from the platen (back of their film holder). A guy told me that they would then only shoot during a declines to 'push' the film flat against the platen, and that was why vacuum was added...so they could shoot at any inclination. Another guy gave me an interesting explanation from his father who flew a plane with a camera, about the nighttime cameras with the f/2.5 Aero-Ektar lens and 'flash bombs'. They dropped a 50 pound flash bomb containing 25 pounds of flash powder, set to ignite at various altitudes. The camera had a photocell of sorts to detect the flash and trigger the shutter. The flashbomb was on the order of 2 million candlepower. Having no practical perspective for this, I inquired if this was noticeable to the subjects being photographed. He said it sure as %@#%^ did - it illuminated the ground to mid-day brightness - they'd shoot maybe 6 shots (on a 3 second or so cycle) and scramble out of there as fast as they could. EGG manufactured a supersized strobe flash which was used (at least for awhile) to make strip aerial photographs. Unfortunately, the Germans did a little calculating base on the repetition rate, and used the results to determine the altitude of the plane. This was turned over to the boys behind the Flugabwehrkanone (that's what the Germans called their anti-aircraft guns, and for which the term `flak'--_not_ `flack'--is an abbreviation). The results were often all too devastating, and the strobe flash experiment was pronounced a less-than-roaring success. I once had a chance to look over the AAF technical manual on this monster, and recall that the reflector was the size of a washtub. I wish I'd checked on the size of the capacitor bank, too. A former-photographer neighbor has a 16 x 20 camera in storage - I'm thinking of asking him if I can take measurements on the film holder, but I will have to rely on a tape measure for the height and width - I don't have a caliper that huge. Take the holder to a reasonably well equpped machine shop. Their depth gauges will likely be too small to rest on the edges of the holder, but they will surely have a parallel bar that will straddle the edges of the holder in at least one dimension. They will then use the depth gauge to take the measurement, and you will have to subtract the thickness of the parallel from the reading on the depth gauge. Take several measurements over the entire film area and average the results. It would be thoughtful of you to post your readings, too. George Arndt ___ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
