Clipped corners on ground glass - why?

[Andrew O'Neill]

Clipped corners are there to allow arrow air to escape when the standards are brought closer together, for example, when focussing. When I built my 14x17, I stupidly omitted cut corners. It was really difficult to slide the rear standard forward. I removed the corners, and all was well. Under the dark cloth, I was impressed with how much air was being forced through the corners!

 

[eli griggs]

I think there's a disconnect among some LF photographers (and some medium and small format mat shooters) in that, they simply do not see that a bellows, is, in fact, a bellows, which is a device that compresses and draws in air (and mold and funguses and dust, etc).

The same thing happens when a one touch zoom is used, which is why it's such a bad idea (IMO) to use moldy lenses on a good camera, or good lenses afterwards a moldy zoom has been used.

 

[DREW WILEY]

Unless you want your camera to double as an accordion, yes, there can be quite a bit of pressure built up when you fully collapse the bellows for transport, especially with flatbed cameras. So that second amenity to having cut corners, releasing the air, can also be significant.

 

[reddesert]

Glass is "seamed" by putting a bevel on the edge to remove sharp edges and stress concentrations. You can do this with sandpaper, or an industrial machine. This is usually a much smaller bevel than the clipped corner. Arissing may be a less common word (or perhaps UK usage) for it.

It is true that some older wooden cameras have a ground glass frame whose inner cutout is rounded or doesn't extend fully flat into the corner. So you need the clipped corner to make the ground glass fit and lie flat. I have a Burke & James wood camera like that. It may be that routing the interior corner to full depth was difficult with the tooling they had. Here is an example on an Eastman camera (not mine). Look at how the surface on which the GG lies, is curved up in the corners. The attached photo is a detail from the full photo at http://www.piercevaubel.com/cam/ekc/1.htm

 

[DREW WILEY]

"Corner chisels" are common enough for squaring routed corners. They existed long before power routers, and today are mostly used in relation to door hinge cutouts. Round-corner door hinges are also made, for sake of high volume installation. However, probably several billion door hinges get installed per every single instance of a view camera being manufactured.

In the case of that lovely old camera in the previous post, no routing was involved, or any kind of router plane; rather, a rabbet plane,
or in incorrect non-American English, a "rebate" plane - send in the coupon and get some money back. I realize that talk like that can be controversial, but it shouldn't make your hare stand on end.

 

[inthedark_06]

Thanks!

I really don't understand about the vignetting thing.

I'll take a look at my P2 tomorrow to see if i can work out what that means!

The corners are used to see if your lens will have any vignetting on the frame, i.e. whether or not your lens has a large enough image circle for the format.
When your image is composed & focused, if you look through the clipped corners & you can see a full circle of the lens, it is large enough. If you only see a part of a circle, you will have vignetting or perhaps even a totally blank area of the film/plate.

And as some others have said, it is also to let air into and out of the bellows.

I am not sure exactly how it works nor how to look for it as my LF camera doesn't have clipped corners, but I know why they are that way.

Regards.