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Shimming septums in film holders?

 
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bartbob



Joined: 30 Oct 2010
Posts: 102

PostPosted: Mon Dec 20, 2010 9:06 pm    Post subject: Shimming septums in film holders? Reply with quote

In checking the 4x5 Riteway film holders I got, a couple of 'em have septum depths from the flats as much as .200" to .201". The 40 year old film that came with my SSG had black .004"thick 4x5" paper between each sheet. After sliding one in the septum of the holders with too much depth, the new depth came up to .196" to .197". Sheet film that's .008" thick slides easily, but with more resistance into the septum atop the black paper that rides on the bottom rails in the septums.

Seems like a decent way to salvage film holders whose septum depth is a bit deep (for me, that's greater than .199"; 2 thousandths deeper than the .197" spec. All 12 of the holders I got now have depth to the effective septums of .195" to .198". That's a .003" spread that's well inside the .014" spread around .197" allowed by ANSI specs. I think any spread over .004" will begin to show image sharpness problems that increase with larger apertures and longer focal lengths.

And with the film held tighter in these modifided septums, it'll stay in place better and not shift around 1/16th inch or more. There's enough clearance in most of the septums to allow gravity to pull the loaded film around as the SSG's orientation's changed.

Comments and suggestions welcomed.

Bart
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