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.

[Len Middleton]

I wonder if there is a secondary reason related to the manufacture of the camera back, as clipped corners are often (always?) on wooden cameras, while non-clipped corners are used often on cameras with metal backs.

If the recess for the ground glass is cut into the wood back with a saw or router, then the depth right in the corners will not be the same as further away from the corner due to the circular shape of the router bit or saw blade, hence the need to clip the corners on the ground glass so that it does not sit out of position (too high).

Maybe those on this site who build cameras could provide some insight...

[Cletus]

It's quite possible for a competent woodworker to produce a sharp inside corner, even if a router is initially used to 'rough in' a recess. That's an interesting point you've made, but I really don't think this is the reason the corners are clipped on the GG.

See: "The Ability to Check Lens Coverage", above, for a full explanation of why the corners are clipped. I think you'll find there are many metal cameras out there with clipped corner GGs.

[Sevo]

I wonder if there is a secondary reason related to the manufacture of the camera back, as clipped corners are often (always?) on wooden cameras, while non-clipped corners are used often on cameras with metal backs.

As far as my cameras go, I cannot confirm that - all my metal age professional view cameras have a ground glass with clipped corners, while many of the old wooden ones have a plain rectangular ground glass.

[Len Middleton]

See: "The Ability to Check Lens Coverage", above, for a full explanation of why the corners are clipped. I think you'll find there are many metal cameras out there with clipped corner GGs.

I do not disagree what it is a useful feature, and indeed one that I use on my wood 8x10 and wood 8x20. But I know that neither of my 4x5 Technika's (previous IV, and now V) nor 4x5 Kardan, nor do any of the Crown or Speed Graphics as per factory units I have seen have that feature. It may be that I have not seen enough different cameras to discern an actual pattern.

Just an open question, from my perspective...

[IanG]

The myth of the clipped corners allowing air flow comes partially from the problems found with the first roll film cameras where opening the bellows could play havoc with film flatness, the bigger the format the worse the issues. A reason why it was always recommended that you only wound the film on immediately before shooting.

Len Middleton's point about the rebate is interesting, my Agfa Ancso can only use glass with clipped corners as the rebate isn't flat right into the corners. My two British field cameras have slight cut-aways under the edges where the glass seats (no clipped corners) to allow easy air ingress.

http://www.lostlabours.co.uk/photography/cameras/images/fc002.jpg
(The crude home-madescreen cae with the camera and has been replaced).

My pre-WWII German 9x12cameras have small breathe holes or groves in the focus backs so it appears many manufacurers thought there was a need to allow air ingress into a camera as the bellows were opened up.

Ian

[Sevo]

But I know that neither of my 4x5 Technika's (previous IV, and now V) nor 4x5 Kardan, nor do any of the Crown or Speed Graphics as per factory units I have seen have that feature.

Interesting. All my Linhofs (and Linhof marked bits of ground glass on other cameras) have cut corners. Is it perhaps a regional fashion more than anything else?

[Len Middleton]

Interesting. All my Linhofs (and Linhof marked bits of ground glass on other cameras) have cut corners. Is it perhaps a regional fashion more than anything else?

Just looked at the B&H site to see what the replacement Linhof groundglass looks like, and the ones shown (many are not) have clipped corners. However they show a 4x5 groundglass frame complete with groundglass, and the corners are not visibly clipped...

Seems somewhat inconsistent, but then I am 6 time zones away from my Linhof, so going by memory and that can be problematic at times...

Not meaning to let my natural curiousity of why things are the way they are, highjack this thread, but it is an interesting question and rife with many inconsistencies in actual practice.

[Cletus]

You can typically specify clipped corners or solid when ordering a new GG. I think it often comes down to personal preference. Some cameras, press cameras for example, don't typically have enough available movements to exceed the coverage of most 'normal' lenses, which kind of negates the ability to check through the corners of the GG. That could be one reason these cameras tend to have standard, ,non-clipped' GGs...just my guess.

Also, I have recently noticed that when using wide angle lenses with standard bellows, such as on my Sinar monorail, the angle is such that you can't see the lens opening from the top corners, even though there may still be adequate coverage of the lens. The fact the the GG is fairly far recessed into the frame doesn't help this, either.

I usually only do this check when using extreme movements, when I might be at or near the limits of the lens coverage. It's quite easy to see when the lens won't fully cover wide open, then as you stop down the entire aperture becomes visible as the IC increases. Quite useful sometimes.

[Jim Jones]

It seems just as easy to check for vignetting by looking at the ground glass through the lens as to do it from the camera's back.

[Sevo]

It seems just as easy to check for vignetting by looking at the ground glass through the lens as to do it from the camera's back.

Well, maybe - if you have a assistant with a flashlight to spare, and only photograph when you can walk all the way around your camera.

[E. von Hoegh]

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.

It is a reliable test of whether or not you have mechanical vignetting. Examining the image on the ground glass with a good loupe is a reliable test of whether or not you have run out of the sharp portion of the image circle.

[Vaughn]

The clipped corners also makes it very easy to see the image in the very corners. The aerial image is much brighter than on the GG.

Also one can see if one's lens hood is going to cut off any of the image.

[Jim Andrada]

AND you can see if something in the camera like a sagging bellows or loose liner is in the way.

[sanking]

It seems just as easy to check for vignetting by looking at the ground glass through the lens as to do it from the camera's back.

Looking through the lens at the ground glass is a sufficient check for most purposes, but it is possible to see the corners of the ground glass and still get some mechanical vignetting with this check. The best check is to look through the corners of the ground glass from the rear and verify that the aperture of the lens is fully visible. If any part of the aperture is hidden there will be some mechanical vignetting. I have never been able to make this determination by looking at the ground glass through the lens from the front.

Yes, this check only shows the circle of illumination of the lens, not the area of acceptable sharpness, but in contact printing that is usually good enough.

Sandy

[Jim Noel]

It is a necessary, but not sufficient condition for coverage. It's useful. That's all.
It is a sufficient if you do more than look at it. if the aperture appears as a cats eye, the coverage is not sufficient. if it is basically round, the coverage is adequate. I have used this since the 1930's and it has never failed to b accurate.

[Andrew O'Neill]

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

And one can check by looking through the lens. When I finished my 14x17 camera, I didn't clip the corners of the GG. Man, was it difficult to slide the bellows out/in!

[Len Middleton]

Interesting. All my Linhofs (and Linhof marked bits of ground glass on other cameras) have cut corners. Is it perhaps a regional fashion more than anything else?

Sevo,

Looking at an old (1950's vintage?) 5x7 Kardan with an 4x5 reducing back (no 5x7 back) I have with a friend here in Africa, it too has clipped corners.

However given the groundglass frame depth to mount the standard Linhof folding focusing hood (this one is without one), with the small amount the corners are clipped, it is not possible to really see well through the clipped corner. Hence it would seem to support the potential it is there to address manufacturing issues.

As noted earlier, with either wood or metal it is possible to modify the corner to bring the glass right to the corner, but given the cost to do that, versus clipping the corners of the groundglass, my experience in manufacturing would expect the clipped corners would be the preferred solution.

Nor would I be surprised with a manufacturer hearlding the result of a manufacturing decisions as a "feature".

But as you rightly indicate, it could be a regional fashion, or it could be related to ground glass size, phases of the moon, etc. (;D>

I do of course understand, that not all decisions made are logical rational economic based decisons...

Regards,

Len

[TheDeardorffGuy]

As someone who actually builds cameras I build them to order. If the customer wants square corners thats what they get. If they want cut corners thats what they get. Years ago I stopped asking why. The answer was the same for both. "I want to see the coverage of the lens."

[welly]

I wonder if there is a secondary reason related to the manufacture of the camera back, as clipped corners are often (always?) on wooden cameras, while non-clipped corners are used often on cameras with metal backs.

If the recess for the ground glass is cut into the wood back with a saw or router, then the depth right in the corners will not be the same as further away from the corner due to the circular shape of the router bit or saw blade, hence the need to clip the corners on the ground glass so that it does not sit out of position (too high).

Maybe those on this site who build cameras could provide some insight...

My Wisner 4x5 field camera (wooden) has non-clipped corners but my Cambo 4x5 and 8x10 has clipped corners.

[rdenney]

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.

It isn't. But modern lenses are barrel-constrained, and provide sharpness to the limits of their coverage, at least down to their coverage-specified aperture (usually f/22). There are much older lenses that are not, but then seeing those defects on the ground glass isn't any easier, even with a loupe, unless the lens is fairly long.

It is a reliable test of whether the corners of the film will be outside that barrel constraint, or whether a compendium shade has been set properly.

Rick "who checks it with a laser pointer these days" Denney