How about just having a glass about a centimeter is front of the film. Then pressurize only the chamber between film and glass. The bellows is free of pressure and the volume is far smaller, yet dust on the glass will be far less obvious and the glass will not be touched so there will be no tendency to develop scratches. A spot will have to be pretty bad to show on the film unless you are working at rather small diaphragm openings.
Continuous pumping is better than "minimally practical" and is used in some good commercial cameras (I suspect most working on precision projects in the larger formats.) It is awkward for normal photography, even in a studio, but I doubt if it is more than a minor problem if well thought out. Bob At 05:27 23.10.01 +0000, you wrote: > >I assume you do realize that pressure or vacuum alone isn't what is going > >to flatten the film. It is the pressure differential between the opposite > >sides of the film that will hold it in place. In other words, you will > >need to ensure that there is less pressure behind the film than in front > >of it. If you make things air tight and simply pressurize the chamber you > >would presumably have the same pressure behind the film as in front of it. > >That doesn't gain you anything. After all, if you do nothing the chamber > >is pressurized according to your local barometric pressure. I'm guessing > >you'd always want to have an air leak behind the film if you want to > >pressurize the film chamber. > >Yes, I understand all this and that's the reason why I'm using the rubber >strips to seal just the area around the film opening in the the front (lens >side) of the back instead of the entire back. > >While some degree of air will always leak out of the pressurized bellows, >the amount that leaks out right now is larger than I'd like since it >requires pumping air into the bellows continously in order to make my setup >work. While this is minimally practical in a studio environment, it's >totally impractical in the field. I know the bellows will need to be >relieved of some pressure between shots in order to allow for focusing and >movements but having to pump it up each time from empty is more work than >I'm willing to undertake, especially with the small rubber bulb I'm hoping >to use. > > >Jeff Goggin >Scottsdale, AZ >_______________________________________________ >Cameramakers mailing list >[EMAIL PROTECTED] >http://rmp.opusis.com/mailman/listinfo/cameramakers _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
