Nominal Sizes?

[jb7]

So I'm toying with the idea of making some film holders for ULF-
and I've been doing some reading-

So I'm surprised that I've got as far as asking this question-
since there's not a chance that I'll be able to cut anything to tolerances measured in thousandths of an inch-
which will be vital, according to some advice I've read-

However, be that as it may, there is one piece of information I've been unable to pin down-

Of the imperial and metric sizes given for some of the common format sizes,
11x14, 14x17, and 20x12,
which is the accurate dimension?

14x17 is usually given as 35 x 43 cm, for example, which it's not-
or rather, it seems like those sort of tolerances might be a bit large-

Any help will be appreciated- might help me finish the easy part of the drawings-

Many thanks-

joseph

[robert fallis]

Joseph,
are you making the holders to fit a camera you already have? in which case make the holder to fit it, the only really accurate measurment is that the film and the ground glass lay in the same plane
If you are making a camera as well as making the holders . make them to fit the back you make, again the only the ground glass and the film need to be in the same plane,

remember you can always cut the film to the size of your holders

bob

[jb7]

Thanks for the reply Bob-

Ideally, should I get past the drawing stage, I'd like to make the holders to fit standard sized cut film-

I would be making the back as well-
so you're right- the important thing is that those two elements match-

The imperial and metric sizes I've been able to find simply don't match up-
one of them has got to be a nominal dimension,
and I'm guessing that it's the metric one-
but I'd like to take the guesswork out, by determining the actual size of the film-

I still haven't made my mind up about the actual format,
but it's somewhere between 11x14, 14x17, and 20x12-

Regarding the important coordinating dimensions you mentioned,
I've determined a methodology that might enable me to get close-
but it would be pretty pointless to build the thing, and then have to trim 5mm off the film to make it fit the holder-

Thanks for the reply, appreciated-

j

[Oren Grad]

Perhaps these will help:

http://home.earthlink.net/~eahoo/page8/filmhold.html

http://www.canhamcameras.com/Film%20Holder%20Specs.html

[jb7]

Thanks Oren-
That's exactly what I was looking for-
well, at least up to 14 17-
they don't include the dims for 20x12 film-

thanks again-

j

[Oren Grad]

For the larger sizes, the convention that's usually stated is for film to be cut 1/16" less than the nominal dimension. In practice, tolerances can be a bit loose, especially from smaller manufacturers and third-party finishers, so you need to allow some breathing room around that.

When you settle on a specific size or sizes, you can ask people here to measure some negatives in those sizes that have been made with film from different vendors.

[jb7]

Thanks Oren-
it seems that there is a minus tolerance on the nominal size, from what I can gather-

You're right, settling on a size is the priority-
still, would be nice to be able to do the drawings to scale, from the beginning-

If I was working from 4x5 I could just go and measure...

j