Vacuum Film Holders : Hole Diameter / Vacuum Pumps

[europanorama]

older discussion here:
http://www.apug.org/forums/forum379/...t-field-3.html

[europanorama]

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.

[Tin Can]

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

Not to steal the thread from Drew but I've made a few of these for my 4x5. I use them for wide-field 4x5 astrophotography. Sheet film can and does move during fifteen minute exposures, so something to keep the film locked in place is manditory.

Standard film holder. Holes are 1/16". One side of the holder has a little piece of plastic sheet with a milled out cavity underneath. The sheet is glued in place to link all the holes together for the vacuum. Suction is provided by a converted aquarium air pump that I modified for a slight vacuum instead of pressure. You can see the suction pattern on the surface of the film in the photos. Battery powered and portable. Been using it for years. It works wonderfully!

I would caution that you carefully check to find a film holder that has perfect registration with the camera's ground glass beforehand. I had several film holders that didn't precisely match up the film with the image on the glass.

[Drew Wiley]

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.

[ic-racer]

This shows the hole pattern on the vacuum easel I use.

[Drew Wiley]

The pattern looks like some of mine, though some have register pins too; and mine are all-black.

[Tin Can]

Synchronicity is real

[Havoc]

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.

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.

[Drew Wiley]

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.

[Drew Wiley]

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.