Peeking in the corners

[Tom N]

I've read that one can look through the cut off corners of the ground glass to make sure there will not be any vignetting. What I'm not sure of is what are you supposed to see to ensure no vignetting? Are you supposed to be able to see the whole back of the lens in each corner or just as long as you a part of the lens?

Thank you all for your time to answer my question.

Tom

[Jorge Gasteazoro]

You should see a circle, if you see an ellipsoid you are getting vignette. I find it easier to grab the dark cloth and peek through the front of the lens, if I can see all 4 corners then I am ok. There has been time when I peeked through the corners and I was sure I was ok only to find out I had some vignette....pissed me off....

Another solution is to move the front standard, up or down and see if you see any dark spots in the GG. This is what I use the most, tired of peeking and looking like fool only to find out I still messed up.

The best solution of course is to sell your house and buy all the Schneider SS XL lenses, you will never run out of coverage with them, at least up to 8x10 and in the case of the 210 XL up to 12x20. ...

Good luck.

[JimL]

I also look through the lens into the corners. My understanding is that if any part of the barrel or rim of the lens or filter is cutting into the aperture opening along the line of sight into the corners, you are getting vignetting.

[Mike Gudzinowicz]

Tom,

If you look at the lens pupil from an angle with the aperture wide open, you'll notice
that portions of the front and rear cells, filters, and possibly the lens hood, intrude
into your view through the aperture. As a result, the amount of light transmitted off-axis
is less than would be expected if the lens were unobstructed. In extreme circumstances
a photograph’s edges will fade to “nothing”… a dark unexposed image. The photo is a
“vignette”.

As the lens is stopped down, eventually you should reach a point where the intruding
elements are no longer visible. At that point, off-axis illumination is limited by the
chosen aperture, and the corners are not excessively dark compared to the center
of the field of view. Although off-axis illumination will be less than the center,
the relationship will be constant, and corners should be fairly well exposed.

If you use a compendium bellows rather than a hood, it should be adjusted by
looking through the corners until vignetting no longer occurs.

Mike