older discussion here:
http://www.apug.org/forums/forum379/...t-field-3.html
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older discussion here:
http://www.apug.org/forums/forum379/...t-field-3.html
Have two MUP 67/220 vers 3 vaccum-backs. concept is totally wrong. wrong pattern at wrong position(check where in RB67/70 vauum-back)
and holes too big. yet to be tested. one has a cross-lines/depression with one hole at center. Contax RTS III has three lines with center-holes. How is it in Contax 645? above all. how to trigger if this back can be mounted on non-electronic camera? there is an adapter.
This is usable data with pictures and not only a mess of words.
Oops needs the attached pics to follow with
https://www.largeformatphotography.i...l=1#post999505
If one uses a standard film holder with the back side converted into a sealed chamber (except for the holes to the film side), it's important to glue in some little struts or shims of correct thickness so that the vac draw doesn't deflect the septum in between.
This shows the hole pattern on the vacuum easel I use.
Attachment 195556
The pattern looks like some of mine, though some have register pins too; and mine are all-black.
Synchronicity is real
What kind of (portable/battery/hand powered) pump do you guys use to deflect the septum? I imagine you do not need enormous pressure differences to keep a piece of µm film that is already substantially flat attached to the septum. Probably you need to suck harder on a straw to drink that what is needed here.
The whole point is to NOT deflect (bow) the septum, but just hold the sheet film secure and flat. I've used various miniature vacs in the lab, but now just use my Festool Midi Vac in the adjacent room at the lowest power setting. I also have a bleeder extension wand for it if necessary. Not cheap, but the real deal if you want a compact certified true Hepa vac that can be used for darkroom cleanup too, without fear of dust escaping. Legal for lead paint removal too, etc.
As per P67 vac backs for astro work, my understanding is that they're intended for 220 film. The backing paper of 120 spoils their precision.