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Greg
9-Jan-2017, 17:12
Does anyone know what the "standardized" distance from the front of a film holder to where the film lies is? My notes have it to be 3/16 of an inch, but I do not remember where I got that measurement from, and I seemed to have misplaced my depth gauge.

thanks

Kevin Crisp
9-Jan-2017, 17:33
http://home.earthlink.net/~eahoo/page8/filmhold.html

DHodson
10-Jan-2017, 07:41
Can you check that link please? It's not working for me.

Thanks
Dave

Dan Fromm
10-Jan-2017, 08:13
I just clicked on the link. It worked for me.

As of a few minutes ago the page has been saved 29 times on archive.org. Their link to the saved pages is http://web.archive.org/web/*/http://home.earthlink.net/~eahoo/page8/filmhold.html

Jim Jones
10-Jan-2017, 08:32
It should be noted that some of the information in this often cited illustration may be questionable. The depth to film surface distance (the "T" distance) as shown in my 1951 copy of the ASA standards is to the back, not the front, of the film. The Exposure Height measurement given is apparently the ASA D2, not the appropriate D3, measurement. The Exposure Width measurement is the E1 maximum, not the appropriate E3 measurement. The Retaining Tab Location is a maximum; the minimum is .010" less. The Length diminsion is a minimum: ASA specified no maximum. The Width is a maximum: the minimum is about .031" less. The Distance to Exposure Field is a maximum: the minimum is .020 less for up through 5x7 holders and .030 less for 8x10 holders. I don't have ASA information on holders larger than 8x10. Diminsions in newer versions of the ASA or ANSI standards may differ. I don't have access to my other reference materialo at the moment.

Leigh
10-Jan-2017, 09:00
The depth to film surface distance (the "T" distance) as shown in my 1951 copy of the ASA standards is to the back, not the front, of the film.
That's because the T distance is to the front surface of the film septum, which is part of the holder.

It has nothing to do with the film, which is not mentioned in this standard.

If you choose to criticize, please understand what you're talking about.

- Leigh

Will Frostmill
10-Jan-2017, 19:58
Er, hrm. Well, which surfaces should I be checking with a micrometer* to figure out if my ground glass and film holder are going to agree?

*a lucky find in my dad's desk drawer!

LabRat
10-Jan-2017, 23:06
Er, hrm. Well, which surfaces should I be checking with a micrometer* to figure out if my ground glass and film holder are going to agree?

*a lucky find in my dad's desk drawer!

That micrometer is useful for checking the thickness of film (which can now vary due to new thinner bases than days of old), but what is required is a DEPTH micrometer set that has interchangeable measuring rods for different depth ranges...

Also (for the fanatic types out there), the surface of the film is not the optimum point for focus, but rather slightly in-between the top & bottom of the emulsion where the image forming takes place... (Some Leica fanatics fight this out online...)

Remember, we are using old view cameras with a lot of slop in alignment, and note that ANSI has allowance for tolerance, and even film can pop with it's chest out, or crestfallen inwards due to the environmental factors, or plain old gravity, so happy Ground Hog's Day film, and you will be where you will be during exposure time... (The film plane is no place for compulsive, nervous, sissies to dwell!!!) ;-I

Steve K

Leigh
10-Jan-2017, 23:33
Also (for the fanatic types out there), the surface of the film is not the optimum point for focus, but rather slightly in-between the top & bottom of the emulsion where the image forming takes place...
The emulsion on a film is only 5 to 10 micrometers thick (that's millionths of a meter).
That's 200 to 400 millionths of an inch.

Considering the thickness of the base is several thousandths of an inch, the emulsion thickness is irrelevant.

For positioning a ground glass, you should set the distance from the rear surface of the camera to the lens side of the ground glass equal to the "Depth to film surface" from the spec (0.197" +/- 0.007" for 4x5 film).

- Leigh

Doremus Scudder
11-Jan-2017, 01:54
Er, hrm. Well, which surfaces should I be checking with a micrometer* to figure out if my ground glass and film holder are going to agree?

*a lucky find in my dad's desk drawer!

Just to elaborate on what's been said and assuming you indeed have a depth micrometer: What you measure will depend on what you are doing; checking/setting your camera's focus or constructing filmholders.

To check camera focus:

Remove the back from the camera and place it with the inside-up (outside/gg side down) on your work surface.

Measure from the flat surface where the back meets rear standard/camera body to the ground glass. Note: this measurement is NOT going to the the same as the ANSI standard for filmholders! It is specific to each camera design. Also, be aware that it takes some skill and practice to use a depth micrometer correctly and consistently. You should master this before making your measurements to eliminate operator error.

Now, insert a filmholder in the camera back, remove the darkslide and make the same measurement: from your chosen flat surface to the surface of the septum that the film rests on. This measurement minus the thickness of the film should be the same as the first measurement to the surface of the ground glass.

Note that it's often easier to check camera focus with a focus test: Set up a ruler at an oblique angle to the camera. Focus with a relatively long lens on the middle of the ruler (at say, the 6" mark). Shoot wide open. Develop and inspect the focus on the negative with a loupe. If the focus is correct, you're good to go. If the focus is farther out than that on the ground glass, you need to shim the ground glass out. Cut and install some shims and test again. Add or remove shims until you have the correct focus. If the focus is closer than that on the ground glass (this happens more rarely), the gg is too far away and you need to move it closer by milling or otherwise removing material on the gg seat. Note that if your camera was designed to have a Fresnel/ground glass sandwich and now doesn't, that this will happen. TIn this case, the best solution is to get a proper OEM replacement rather than modifying the camera.


If you're building filmholders:

You should use the standards given by ANSI, and the depth to measure is from the front outside surface of the filmholder to the surface of the septum.

Best,

Doremus

Leigh
11-Jan-2017, 02:36
Remove the back from the camera and place it with the inside-up (outside/gg side down) on your work surface.

Measure from the flat surface where the back meets rear standard/camera body to the ground glass. Note: this measurement is NOT going to the the same as the ANSI standard for filmholders! It is specific to each camera design.
Sorry, Doremus, but I don't understand your comments.

The distance from the back of the camera (where the filmholder rests) to the film surface is a constant for each film size. If that wasn't true we'd need different filmholders for each brand of camera, and perhaps for each model.

The dimension is given in the filmholder spec as "Distance to film surface".

And I don't understand your instructions for making the measurement.

- Leigh

John Layton
11-Jan-2017, 07:54
Back when I started designing cameras...I'd developed my own protocol for determining the "best" measurements to determine ground glass/focussing surface depth, which involved hiring out a very sophisticated ruby-tipped probe/laser-guided measuring gauge - and then measuring depths from film holder contact planes to actual film surfaces, to several locations across these film surfaces, and doing this with a variety of different manufacturer's holders, different film types, different atmospheric conditions, and holder orientations. I then averaged everything out...then further biased my "standard measurement" based on my own assumptions about how large format cameras are most typically used (orientations/conditions/etc.)

The reason for my "paranoia" was a hunch that films rarely behaved in a manner that would be in any way served by making assumptions based on theoretical "constants." My hunch was correct.

Try this - place a loaded film holder on a flat surface, pull the dark slide, and place a strong light...obliquely so that its angle of incidence creates some specularity on the films surface when viewed. Now, preferably while wearing magnifying glasses, viewing closely from as low an angle as possible, take a sharp tipped instrument (a sharp pencil is fine), place its point very gently against the films surface...and then push down. See that? Now...try this at several locations over the length and breadth of the film. See that? You gotta look really carefully. Now...see that? Just a bit of a dimple? A bit more in the middle...a bit less near the edges? Not always...but more often than not?

My conclusion? That the only way to trust a measurement based soley on film surface above septum height would be to add to this an additional thickness of some very flat and reliably stable (over time and a variety of conditions/orientations) double stick tape! (didn't Linhof try this awhile ago?)

Finally, while I will not pretend to give actual advice - I'd recommend doing the above test - and maybe take some measurements (no need for the fancy test equipment...a good straight edge and measuring square are fine), using your own favorite film holders and film types - and then make or have made any indicated adjustments to the distance from the ground glass focus plane to the rear plane of the ground glass frame.

John Layton
11-Jan-2017, 08:25
PS - in performing the above-mentioned test...be very careful to divert your breath away from the film! Moisture from your breath will affect your results!

Leigh
11-Jan-2017, 10:30
Back when I started designing cameras...I'd developed my own protocol for determining the "best" measurements to determine ground glass/focusing surface depth
So you chose to violate industry standards, thinking that your minimal testing produced more valid results than extensive well-financed industry tests that were structured and vetted by industry experts ???

Interesting.

How does that conform to the doctrine of "interchangeable parts", meaning that any standards-compliant product will work with any other?

Glad you're not designing automobiles.

- Leigh

John Layton
11-Jan-2017, 12:53
Leigh…jeeesh! “Violate?” is a pretty strong word…no?

But I can appreciate where you might be coming from…and although my L-45A still exists only as five prototypes, the issue of standards compliance has indeed been fully addressed to cover the (however exceedingly remote) possibility that I might bring this camera into production. And no, I will not share the specifics of this.

Do know that I have some real concerns relating to the often dynamic nature of a “flat” sheet of plastic…and know also that my aforementioned testing process involved not only a very impressive machine - vibration isolated…weighing several tons…optically flat surface…compensation adjustable for different temperatures, etc. etc…but that this machine came with a very qualified, certified operator.

In the meantime…do note, in my original text, the quotes around the word “best.” I am merely stating that I have found my own, “best” means to help ensure that I realize the level of reliability and consistency that I need for my own work, and that, in the spirit of this forum, I feel compelled enough about my results to share this information with a larger community of artists/photographers, in the hopes that I might contribute something useful to the continuing evolution of a truly productive, critical, and fulfilling exchange of ideas. Make sense?

Leigh
12-Jan-2017, 02:18
John,

what you apparently fail to realize is that published standards are not a chinese menu.
You can't pick and choose which items you want to follow and which you want to ignore.

A product is either standards compliant or it is not. For a view camera, that compliance would be in the location of the ground glass relative to the camera back, i.e. the holder seating plane.

The problem I have with your extensive analysis is that it tells you nothing.
All the detailed investigation in the world only tells you what the sheets are/were when tested.

It tells you absolutely nothing about the film you might pull out of the next box.
The information does not constitute a valid data set for product design because it is not predictive.

- Leigh

Doremus Scudder
12-Jan-2017, 02:37
Sorry, Doremus, but I don't understand your comments.

The distance from the back of the camera (where the filmholder rests) to the film surface is a constant for each film size. If that wasn't true we'd need different filmholders for each brand of camera, and perhaps for each model.

The dimension is given in the filmholder spec as "Distance to film surface".

And I don't understand your instructions for making the measurement.

- Leigh

Leigh,

In the instance that seems confusing, I'm not talking about measuring from the filmholder seat (the plane against which the filmholder rests), but rather the flat surface that mates the "back," that is the entire assembly that holds the spring back, to the rear standard or camera body. The distance from this plane to the septum in the filmholder/ground glass is therefore greater and varies from camera to camera. The advantage here is that it is easier to measure with a depth micrometer as you have two planes facing the same direction; simply rest the depth micrometer over the opening and measure to the ground glass and, after inserting a filmholder and removing the darkslide, to the septum. These two measurements should agree minus the thickness of a sheet of film.

Of course, the distance from the filmholder seat to the ground glass is the same as from the seating surface of the filmholder to the film. This, however, is not what I'm suggesting measuring.

Hope that clears things up.

Doremus

Leigh
12-Jan-2017, 02:50
In the instance that seems confusing, I'm not talking about measuring from the filmholder seat (the plane against which the filmholder rests), but rather the flat surface that mates the "back," that is the entire assembly that holds the spring back, to the rear standard or camera body. The distance from this plane to the septum in the filmholder/ground glass is therefore greater and varies from camera to camera. The advantage here is that it is easier to measure with a depth micrometer as you have two planes facing the same direction; simply rest the depth micrometer over the opening and measure to the ground glass and, after inserting a filmholder and removing the darkslide, to the septum. These two measurements should agree minus the thickness of a sheet of film.
Hi Doremus,

Yes, I agree. I wasn't sure from your previous description.

I really didn't expect an error, since I'm accustomed to you posting accurate information.

Thanks. Sorry for the confusion.

- Leigh

John Layton
12-Jan-2017, 06:39
Leigh…my sincere apologies - to you and to everybody - for my arrogance; for purporting to be “correct” (as in, “my hunch was correct,” and “the only correct way…”).

I will do my best, in the future, to share any experimental results as what they are - experimental results…with the caveat (and promise) that I will never, ever, assume that any kind of “standard” cannot be questioned…nor that these questions cannot be acted upon with well intentioned, thorough (to the best of my available knowledge/resources) experimentation, nor that, especially to the extent that this experimentation might produce compelling results…I cannot act upon and/or share these results with others (again, not as “correct”, but as “compelling”)…especially in the spirit of a DIY thread such as this one. Fair enough?

LabRat
12-Jan-2017, 06:46
Leigh…my sincere apologies - to you and to everybody - for my arrogance; for purporting to be “correct” (as in, “my hunch was correct,” and “the only correct way…”).

I will do my best, in the future, to share any experimental results as what they are - experimental results…with the caveat (and promise) that I will never, ever, assume that any kind of “standard” cannot be questioned…nor that these questions cannot be acted upon with well intentioned, thorough (to the best of my available knowledge/resources) experimentation, nor that, especially to the extent that this experimentation might produce compelling results…I cannot act upon and/or share these results with others (again, not as “correct”, but as “compelling”)…especially in the spirit of a DIY thread such as this one. Fair enough?

What!?!!! Good observations/instincts!!! Film does flop around, and finding an average position/plane is a worthy pursuit...

Thanks for sharing your experiments/experience!!!

Steve K

Leigh
12-Jan-2017, 10:30
Leigh…my sincere apologies
Hi John,

No such required.

The point I was trying to make was that when industry standards exist, you're obliged to follow them in any design that claims to be usable with commercially-available accessories such as filmholders.

Thanks.

- Leigh

MAubrey
12-Jan-2017, 11:07
you're obliged to follow them in any design that claims to be usable with commercially-available accessories such as filmholders.
Did John make such a claim in his post???

Leigh
12-Jan-2017, 17:20
Did John make such a claim in his post???
Yes

He's talking about the position of the ground glass, which is intimately related to the film holders in use. Unless he's making his own film holders, which he doesn't claim, he's obliged to match the standards for commercial holders.

- Leigh

John Layton
12-Jan-2017, 20:08
OK...I need to cut to the chase and then leave this discussion. At this point in time, I am under no obligation, to anyone, to comply with or to state, or claim, (or otherwise prove) that I have ever complied with any kind of "standard." If I feel that I want to change something (even a "standard") that already exists, I am completely free to do so. If I feel that I can improve on something (even a "standard") that already exists...I am completely free to do attempt to do so.

Its all a matter of context.

If you disagree with this...then I urge you to please go back and re-read my earlier posts very carefully. If, after then, you still disagree...then we obviously have a difference of opinion - and, as a matter of principle, I am completely OK with that.

Now...time to move on - gotta get some sleep, so I can wake up refreshed, get back to the work that needs doing, and be ready for when the next inspiration hits!

el french
13-Jan-2017, 01:19
I'd be surprised if the average measurement made by @John Layton was not within the tolerances of the standard.

Pfsor
13-Jan-2017, 06:59
OK...I need to cut to the chase and then leave this discussion.

Now...time to move on - gotta get some sleep, so I can wake up refreshed, get back to the work that needs doing, and be ready for when the next inspiration hits!

I'm with you on that, John. No sense in letting yourself be chased by a pack to defend what others cannot simulate. Cheers!