Randy, I'm pretty sure those are correct,but you can easily check if you have a modern 8x10 holder. My understanding is that there may be some variance in older holders (i.e. pre 1930). I didn't use these when I made my back, just measured the fidelity holders I had. I'm in the US now for three weeks, so cannot check mine.
Measuring existing film holders in hopes of deriving the correct film holder dimensions can introduce errors. Some of the data in the link cited in post 90 are incorrect. The value for "depth to film surface" is actually the "T" value, the depth from the film holder's face to the septum surface. This means a .012 error, the width of the film slot. The value for "Exposure height" is obviously wrong; it is actually the D2 value, the maximum long dimension of the film slot. The 8x10 "Exposure height" should be 9.575. The "Width" value is the maximum: the minimum for film holders up to 8x10 is .031" less. My figures come from the copyrighted ASA Z38.1.1951 spec sheet, which lists sizes only up to 8x10. Perhaps a good researcher can find newer freely downloadable official specs online.
These come from a 1998 version from ANSI. They *are* the standard.Originally Posted by Dan Fromm
And they are also wrong! Or at least listed incorrectly.
Using the 8x10 data as an example:
Distance to Exposure Field: 0.775"
Exposure Height: 10.026"
Sum of the two: 10.801"
Distance to Tab Location: 10.850"
That leaves only .049" (1.245mm) between the upper edge of the exposure field and the upper edge of the retaining tab. Look at any film holder and you will see that this cannot be correct! This figure should be in the vicinity of .375" or more.
Using the Exposure Height figure mentioned above by Jim Jones (thanks btw!) we now have:
Exposure Height: 9.575"
Distance to Exposure Field: .775"
Sum: 10.350"
So now the distance between the exposure field and the retaining tab is a more plausible .500".
Yes. Because they are not correct.
Jim Jones has it covered.
Thanks Jim!
Tin Can
Here's a link to information S&S uses to make their holders:
http://ssfilmholders.com/?page=documents
Unfortunately they do not list specs for 8x10 holders. The measurements may or may not be the same.
I haven't done an exhaustive search, but I have rooted around the web several different times and have been unable to find a reliable set of specifications, this is why I think taking measurements from a number of different brand holders and "averaging" the results may be the simplest solution.
This thread caught my eye while I was googling for general camera designs the other day. I've yet to work with large format, but I'm finding myself more than a little interested in the entire process as something different from the usual sports photography I do.
I honestly have no idea what kind of camera I actually would want, but I do know the end results that I will be looking for eventually would be black and white landscape prints in the order of 'insanely huge and rather dominating in a space'.
As for the 8x10 holders, could the detailed specification not be avoided by designing a scalable back frame? You don't need to design the camera to take every 8x10 holder on the market, it just needs to be able to accept the 8x10 holders of that you are actually planning to use.
Maybe get a google form and spreadsheet going and let people submit detailed measurements of all of their existing holders, and then you can define a specification range off of those. Then the end user would either build their back frame to accept the holders they own or are planning to get, or use a larger frame that accepts sub-frames if the range of holders is large enough that there isn't a reliable 'one size fits all' kind of option.
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