Ground Glass - clipped corners, or not?

Sanjay Sen

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What is/are the benefit(s) of clipped corners on a ground glass? My Zone VI GG does not have clipped corners, but the Wehman does, and I did not notice the difference until I checked them.

So why do some ground glass have clipped corners, while others don't?


Thanks for any info.
 

Mick Fagan

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I use the clipped corner to look through and see if the coverage of the lens covers the extreme corner.

It is a facility I use quite a lot, especially with my particular 90mm lens on anything other than straight alignment.

Mick.
 

Vaughn

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I like them for the same reason as Mick -- as well as making sure one's lens hood is not blocking part of the image-forming light. One can also see how small an aperature one has to go down to avoid vignetting.

And lastly, for composing, I can see an aerial image in the corners which is much brighter than the image thrown on GG. I am very near-sighted, so I do not know if this (using the aerial image) is possible for those who are normal-sighted.

Vaughn
 

Anscojohn

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*******
It is my understanding the clipped corners allow rapid focussing without collapsing the bellows due to negative air pressure when moving the GG away from the lens.
 

Ian Grant

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Anscojohn said:
*******
It is my understanding the clipped corners allow rapid focussing without collapsing the bellows due to negative air pressure when moving the GG away from the lens.
Click to expand...

I think that's an "Urban Myth" perpetuatedin many publications, because many old field cameras didn't use clipped corners, and non of my 5 German 9x12 folders and there's no problems with the bellows when opening/closing quickly.

A 3 of my Graphics (Speed/Crown) have unclipped corners.

The clipped corner was more essential for checking coverage with older lenses particularly EWA's (WA Protars etc) often with maximum apertures of f16.18, or less in the case of Hypergon. With no fresnel screens to help it was almost impossible to see the image at the edges & corners check coverage with movements.

Ian
 
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Sanjay Sen

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Sorry if I don't understand this correctly, but can I not check if the lens covers the extreme corners by checking the GG itself? For instance, last weekend I was out with the Zone VI (which does not have clipped corners) and a 90/8 lens, and I verified that I have corner coverage by looking at the GG corners (I'd used some front rise). I am probably missing something here, but not sure what...
 

Philippe-Georges

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I do not consider this is an ‘Urban Myth’.
I have seen this happen in photo school, in the late ‘70, with a Linhof Cardan Colour 13 x 18 cm, with unclipped GG corners.
A fellow student, who apparently was in a hurry, pushed, after turning louse all the knobs on the monorail and the lens still mounted, in one movement the camera from full extension for a close up shot, back in to ‘ready to pack’ position. Not only the GG collapsed but the bellows were blown out too.
But, of course, the GG’s corners are clipped for checking the vignetting of the image circle and the compendium, not for playing accordion...

Philippe
 

Ian Grant

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Of course you can check that way Sanjay, but some older cameras and lenses would not give as bright an image on the screen, try stopping your 90mm down to f16 and then focussing.

Many EWA's like the Protar's and Hypergon's were wider still and that makes the light fall off even worse, so clipped corners are then more useful. A modern equivalent would be a 65mm f8 Siper Angulon, these are hard enough to focus at the cntre of the sreeen and very dim at the corners and coverage is very tight, here the clipped corner helps.

Ian
 

David A. Goldfarb

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It's often hard to distinguish vignetting from falloff of illumination on the groundglass, particularly with wide lenses, but if you can see the aperture through the corners, you can tell more positively. Ideally, you want to be able to see the whole aperture from the corners. If you can see the lens hood or part of the lens barrel, then you have vignetting, which you may be able to correct by stopping down or using smaller camera movements. If the aperture looks like an American football, rather than a circle, then you will have falloff of illumination, and you may want to stop down, use a center filter, or increase exposure to be sure you have detail in the corners, so you can fix it in the darkroom. You can also catch situations where the bellows are obstructing the image more easily with cut corners.

I agree that the "air pressure" factor is not relevant in most cases, particularly with older wooden cameras that may be light tight, but certainly aren't airtight. One case where it is relevant, though, is with the Sinar shutter, where it is possible to damage the large shutter blades by expanding the camera too quickly. The Sinar groundglass is oversized, so it's a bit easier to see vignetting, and the corners of the groundglass are clipped enough to let air in, but not enough to make it particularly easy to see the aperture, though it's possible if you get close and squint.

If you want to check for vignetting directly and don't have a clipped groundglass, you can also sight in the reverse direction. Look through the lens and see if you have an unobstructed view of each corner of the groundglass frame.
 

Thingy

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Ian

You need a Maxwell HI-LUX Ultra Brilliant Matt 4.7 focussing screen. With most of my lenses I don't need to use the focussing cloth, and it gives a bright image in the centre even with my Schneider 120mm HM macro lens!

Steve
 

Ian Grant

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Steve, I can focus a WWI Ross (A.M.) f16 158mm on my 1ox8 camera easily with a Beattie screen even in indoor lighting and no focus cloth, but with a plain glass screen it's much harder

One of my German 9x12's has a deliberate small hole in the metal work of the focus screen holder to allow air in/out during opening/closing.

Ian
 

Mainecoonmaniac

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From my experience on my Sinar F, when I collapse the bellows, air would escape from the clipped corners. I assume it's for the air to escape when you collapse the bellows and it will allow the camera to expand the bellows by allowing air to enter the camera. I would imagine that extending the bellows before shooting and collapsing would be difficult if the clipped corners weren't there.
 

Vaughn

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I don't have clipped corners on my 8x10 -- but will if I need to replace the glass some day. It also might help with another problem I come across occasionally when taking my camera out from behind the Redwood Curtain to somewhere where the sun actually shines. The first time I set the camera up in the sun, as the sun heats up the black bellows, steam starts to form inside the bellows, coating the GG and the back of the lens. Perhaps clipped corners would allow the steam to escape!
 

David A. Goldfarb

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Clearly, Vaughn, you need a tropical camera made out of teak with a light tan leather bellows and an engraved brass plate describing it as a "tropical camera."
 

Thingy

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Steam inside the bellows? You must have one of those exotic bellows made in Finland......





.....with built-in sauna!
 
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Sanjay Sen

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Interestingly, I was reading "The Camera" and AA states the following in the last paragraph of page 37 (2004 paperback printing):

"Particularly in some older cameras, the corners of the ground glass may be cut off to permit the movement of air when the bellows is expanded or collapsed. Obviously, this interferes with seeing the corners of the image. It is better, instead, to have small holes drilled in the ground glass if needed to permit air flow (with most cameras, however, vents are provided)."

So, it appears that AA did not favor clipped corners on the ground glass.
 

jdimichele

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I'll put my vote in for non-clipped corners. I personally find it distracting when I'm examining the ground glass. I also don't buy into the "explosion from quick bellows collapse" story. If you're careful with your equipment there really isn't a point in not spending the extra second or two with collapsing the bellows.


Cheers,
Jay
www.jasondimichele.com
 

Vaughn

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Thingy said:
Steam inside the bellows? You must have one of those exotic bellows made in Finland......)
Click to expand...

I'll be focusing the image, studying the composition and notice it gets more and more difficult to see a sharp image on the GG. Finally it will dawn on me what's happening, and I take the lens and camera back off and let the steam escape and condensation of the GG and back of the lens evaporate.

One good thing that happens when I temporarily escape from behind the Redwood Curtain is that the legs of my Ries Tripod becomes a lot easier to pull out. The wood tends to absorb a little moisture and get sticky in our moist climate -- probably need to refinish the legs someday.

Vaughn
 

ic-racer

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For 8x10 I'd be lost without clipped corners. As an example, when using one of the popular 210mm lenses in copal 1 on 8x10, you can see all 4 crescents and can clearly tell if the image circle is not perfectly centered (as it needs to be when the image circle is only 300mm) This is nearly impossible to do without the clipped corners.
 
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