checking for vignetting

**terry_5379** · 23-Oct-2005, 03:45

when i check for vignetting through the cutout corners when i have used tilt for a landscape, do i check bottom corners of screen or top, i get difference of two stops if i look through bottom corners compared to top, ie 16 at bottom 32 at top.
Thanks terry

**Henry Friedman** · 23-Oct-2005, 06:21

Stop down to the indicated aperture stop and leave the shutter open. If you can see all of the opening through all four cutouts you are good to go. There's no need to meter anything.

**adrian tyler** · 23-Oct-2005, 08:03

will it work also to look through the lens "backwards" to see the inside four corners of the ground glass?

**Alan Davenport** · 23-Oct-2005, 20:05

...will it work also to look through the lens "backwards"

Yes, absolutely. In fact, that's the "correct" way to do it if you want to be completely true to the retro origins of the sport. St. Ansel himself said that the cut corners (in the groundglass) were to allow air to escape when you made large adjustments to the bellows extension; AFAIK he made no mention of looking through the cut corners for vignetting.

IOW, you can do it either way. Sometimes it's easier to do from one side or the other, but it makes no difference to the outcome.

**Mark Sawyer** · 24-Oct-2005, 01:36

Mind you, you're checking for illumination to the corners, not necessarily usable coverage. Many lenses lose resolution at the outer edges of the circle of illumination, hence a smaller circle of coverage. That said, I often check all four corners, especially if using much for movements or using a lens that barely covers.

**Mike Kovacs** · 24-Oct-2005, 11:21

Looking through the front does not show if your lens hood or filters are vignetting your lens, does it?

**Mark Sawyer** · 24-Oct-2005, 13:15

"Looking through the front does not show if your lens hood or filters are vignetting your lens, does it?"

Yes it does, unless you're putting your eye inside the hood or filter rim. The light-path from the gg corner to your eye is the same as in the reverse direction, so if you can see into the corner, the corner can see out to you, (or to the subject, presuming you move your head out of the way...)