Hi all,
what would you suggest as a max thickness for a ground glass of a ultra large camera.
The ground glass is going to be about 20 x 20 inch.
I would prefer 2mm but that is going to be too thin ??
alex
Hi all,
what would you suggest as a max thickness for a ground glass of a ultra large camera.
The ground glass is going to be about 20 x 20 inch.
I would prefer 2mm but that is going to be too thin ??
alex
That sound too thin for such a large camera. Not that I have any experience larger than 8x10.
I have no experience with format that large, but even with 4x5 would be concerned that 2mm may be too fragile. Also, may bow and throw your focus off when you put a loupe to it. Since the ground side is toward the lens the thickness shouldn't matter too much. I'd err toward increasing the odds of survivability and go thicker.
After some checking up on it - the "normal" classical home windows in Europe have 3 mm thickness. They are washed/touched with no special precautions, hence...etc.Originally Posted by alex from holland
As far as I know, here it the U.S., a typical window pane is 1/8th inch thick which is a hair over 3mm also. And, as noted, take a fair amount of "use" over a pane area much larger than a GG.
Alex,
The thinner, the better, as far as brightness goes. For what it's worth, a view screen doesn't have to be glass. A thin sheet of plastic stretched over a frame, like the head of a drum, for instance, would do just as well, and be much brighter, lighter, and much less fragile. This is a feature of all my lightweight camera designs.
Jay, just plainly curious - what kind of plastic you have in mind that can be stretched so tightly that it doesn't bow under a loupe pressuring on it?
The Ritter 7x17 I have on loan uses plexiglass. There are trade-offs for the lightness and the lack of worry about breaking glass, but one could use glass in the studio and plex out in the field.
wow, interesting thoughts.
I have tried grinding a plastic groundglass, but without succes.
How do you guys solve that problem ?
Jay, i would love to see some pictures of your solution. Sounds just great.
alex
GPS,
Mylar is the most commonly used material in this type of application; it's optically clear, durable and can withstand high tension membrane stresses, and it's heat-shrinkable. Push on the head of a drum sometime, and see how much force is required to flex it. A loupe is not a problem.
Alex,
Mylar, and many other plastics can be chemically etched to produce the required tooth to form an image. Very fine etchings are brighter than coarser ones, but create hot spots. A fresnel is typically used to even out the light, but costs a little brightness. An exotic solution is two films, one etched, one fresnel, but a perfectly serviceable screen can be made with just drafting mylar, which comes with a tooth for taking pencil drawing (good for making grids, etc). I'm at work in Alaska right now, so I don't have photos, but once you see a sheet of drafting mylar, you'll understand how it works. I'll make some photos when I get home.
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