ANSI Film Holder Details

[Pere Casals]

I’d think the variance in the thickness of the film should be well within the tolerances. I have no data though.

Still I’d love to see the original ANSI spec, especially to see if there are more details.

The tolerance is for the Septum position, not for the film position, the Septum can be at the limit of the tolerance because manufacturing variability, plating flatness, etc.

The actual tolerance we have for film surface position is on film DOF, considering our desired CoC, measured from the GG inner side.

Then we will not place exactly our film surface where the frosted GG surface was, because we have a variability from the holder (septum) tolerance added to the film thickness variable and flatness miss.

There is an specification missmatch between the GG position from the flange vs the "depth to the septum". This difference is just the "theoric" film thickness.

IMHO this is the source of all confusions, one value is for holder manufacturers and the other one is for camera manufacturers. The discrepance allows Kodak and Ilford to put the emulsion on a plastic base of a certain thickness.

Regarding that, perhaps the thick RX film may require a focuss correction, I don't know if RX shooters are aware of that...

[Jim Jones]

I've used sheet film varying from .004 to .010 inches thick. This, in addition to the +/- 0.007 tolerance in the "T" dimension and the 0.012 width of the film slot, makes precise positioning of the film impossible. Some of the alternate methods of accurately positioning the film are mentioned here :https://www.photo.net/discuss/thread...holders.29599/. Another possibility would be a film holder with the film pressed from behind into close contact with a glass plate. The glass plate may need anti-newton ring surfacing on the rear and multi-coating on the front. What a pain to keep it clean! Perhaps some of the techniques needed to fabricate integrated circuit masks could be modified to be practical in sheet film holders, but that's beyond my experience.

[Jac@stafford.net]

[... snip helpful information ...] Another possibility would be a film holder with the film pressed from behind into close contact with a glass plate.

That's one method used for a 5" military aerial camera: the film is tightly pressed against a Réseau plate, exposed, the pressure plate is withdrawn, film advanced - repeat. I have such a plate and it is amazing. Unfortunately I can't remove the fiduciary markings.

[Nodda Duma]

Jim good analysis method but your conclusion about tolerances doesn’t jive with reality. If it was impossible to position film at the proper distance then we’d rarely see focused images at say (DoF calc) f/16 without Herculean efforts on the part of the photographer to select and trim/shim film holders and the specific sheets of film.

On the contrary, you can get well focused shots at f/5.6 for 4x5 as long as your ground glass is shimmed properly, with whatever holder you slap in there loaded with who knows what and over a wide range of temperatures (thermal expansion).

So what are the real tolerances stack-ups controlled to? They *must* be less than .005” or so if you start digging into the math.

[Pere Casals]

I've used sheet film varying from .004 to .010 inches thick. This, in addition to the +/- 0.007 tolerance in the "T" dimension and the 0.012 width of the film slot, makes precise positioning of the film impossible.

Anyway it's very difficult to adjust 0.2mm with the focusing adjustment, and if the subject has some depth then it's irrelevant... also for sure a regular view camera has more than a 0.2mm alignment mismatch from corner to corner.

I guess than regarding film flatness it is important to have it curled in a way that that sides are elevated compared with center, in that way it remains perfectly flat, in the same way that paper in easels.

Another way is spraying 3M Re Mount glue to emulate Sinar adhesive holders...

[williaty]

This thread also is reminding me that there's a good reason I find it a bit frustrating to shoot portraits with a 150mm f/2.8 on 4x5"!

[Tin Can]

This thread also is reminding me that there's a good reason I find it a bit frustrating to shoot portraits with a 150mm f/2.8 on 4x5"!

If we listen to Pere, we all must give up and let Pere take all the pictures.

Sorry Pere, but the detail you extend is often overbearing.

Your posts make good reading yet are very difficult to conceive.

Don't stop! Just think.

[Pere Casals]

If we listen to Pere, we all must give up and let Pere take all the pictures.

Sorry Pere, but the detail you extend is often overbearing.

Your posts make good reading yet are very difficult to conceive.

Don't stop! Just think.

Randy, it is not mandatory to read all what I post, that's optional

Anyway this has been an interesting thread, there is a discrepance in the GG to flange vs depth to Septum specification, what's me I finally learned why.

[Tin Can]

Randy, it is not mandatory to read all what I post, that's optional

Anyway this has been an interesting thread, there is a discrepance in the GG to flange vs depth to Septum specification, what's me I finally learned why.

I think the loss of ANSI continuity is a problem.

I collect film holders, or rather for a year I collected film and plate holders. Many variations. I have Hasselblad film holders, Hassy quality, spring backed plate septem 2.5 insq. Sharp negs. PITA

Horseman sold a camera that only can accept a wood holder, not a plastic one, missed it by that much...almost invisible with both in hand. PITA

And up to ULF. Big variations. PITA

I have measured many holders and cameras. I have a Deardorff S11 Factory 11X14 back that is 0.125" short, meaning too close to GG. I had a new one made. I could have shimmed. PITA

What we need is what we used to reverse engineer auto engine parts. I never used it, as it had a dedicated user in a clean room. But I would love to see what really is going on, on the septum surface. PITA

The company was USA based and owned, copycat was invented here. Stealing Engineers a favorite ruse. Counterspies. Spy vs Spy. PITA

After a while we just want a product, fix it next iteration. PITA

So it goes.

PITA = pain in the ass

[animaux]

I think the loss of ANSI continuity is a problem.

Aparently the ANSI-spec has been transfered to the PITA, with all its infamous consequences.