Why does the ground glass lack four corners?

[qinghua]

why the view Grid Ground Glass lack 4 corners ?

[qinghua]

why the view Grid Ground Glass lack 4 corners ?

[Dugan]

The ground glass lacks four corners for two reasons:
One is to prevent the bellows from expanding or collapsing when focusing. Some cameras have tight tolerances, almost air-tight.
The other reason is so that you can check for vignetting. When set up to take the photo, if you can see the complete aperture through all four corners, the will be no mechanical vignetting. This is useful when using filters, lens hoods, etc.
I hope this helps.

[Tin Can]

Not all do. Some like cut corners for at least 2 reasons

We can use a corner to see the aperture and they allow less dust with bellows vacuum

[Oren Grad]

Threads merged.

qinghua: Please don't start start threads with the same question in more than one subforum... thanks.

[Tin Can]

'this this' I do that all the time

[Havoc]

I would think they cut them to avoid the weakest point of the glass. A bump or pressure on the corner is the best way to crack glass. Also less sharp points during production, transport and repair.

[Tin Can]

Some GG Frames have raised corners not allowing GG with square corners

Most seem deliberately designed and manufactured with that 'not' a flaw

Look at a few

[Paul Ron]

because large format is so tedious, they need to cut corners anywhere they can.

[John Layton]

I'd prefer square corners...but I do like to be able to check coverage when using "extreme" movements.

As for the other issue...that of air compression/suction exploding/imploding one's bellows (ouch!) - there is another very easy solution, without cutting (ground glass) corners. Simply cut some air relief channels in the underside of your ground glass frame - on the film insertion side. Obviously easier with wood...but in designing my L-45A camera, I incorporated this feature so that I could preserve the squared screen corners.

Of course, my next move is to insert some accordion reeds into these channels - would make the act of focussing a musical event!