Clipped corner ground glass

[jk0592]

Pardon my ignorance, but I wonder what is the purpose of clipped corner ground glasses.
What advantages do they confer compared to a regular, rectangular ground glasses?

[Andrew O'Neill]

Clipped corners allow air to flow in and out of the bellows when you focus.

[Erik Larsen]

If you can see the entire aperture opening while looking through the corner clip you should be assured of adequate lens coverage.
Erik

[climbabout]

If you can see the entire aperture opening while looking through the corner clip you should be assured of adequate lens coverage.
Erik

This to me is the most important reason - I check this all the time when using anything more than moderate movements.
Tim

[jk0592]

I agree with Tim,
because this may otherwise affect the image on the film.
The piston effect would not be so important because the camera is not really airtight, at least not the Cambo that I have.
I just did check to see the lens aperture through a clipped corner, a neat trick.

Thanks to all.

[TheDeardorffGuy]

This is just so enjoyable to read for the 30th time. I get phone calls about it too. The back is not air tight at all on any camera I've seen in 40 years. I got a Speed Graphic when I was 18 and my first Deardorff at 19. When I saw the cut corners I knew right away to look in them to see the lens. If I couldn't there was no coverage. Its a check I do on EVERY image I shoot. Please start looking at your cameras. Learn all the movements. Shoot some film. Look at the results. LOTS of film. LEARN BY EXPERIENCE. Please. I had a mentor at age 17. I used to ask questions. Lots of them. Then he gave me 20 rolls of Panotomic X and told me to shut the hell up till I shot and printed them in 5x7, all of them good and bad exposures and compositions. It took months. I never had to ask him another question. We became great friends till his death.

[Kuzano]

The linhof back and ground glass I have on a homebuilt camera has an interesting ground glass. It does not have clipped corners, but It has a clear X on the back from corner to corner, extending out to all four corners. The X is not frosted, but is two 3/32 clear glass lines. I am sure the ability to look at the aperture from any place on the back is the primary reason.

[C. D. Keth]

If you can see the entire aperture opening while looking through the corner clip you should be assured of adequate lens coverage.
Erik

Lens coverage or lens illumination? I don't see how that could possibly be a reliable test of whether you've run out of the sharp portion of the coverage circle.

[BetterSense]

It is a necessary, but not sufficient condition for coverage. It's useful. That's all.

[pelagic4]

If you can see the entire aperture opening while looking through the corner clip you should be assured of adequate lens coverage.
Erik

Thanks Erik, for that. Something that i could'nt guess at all.