LF technique question

[Alex Hawley]

Sounds like bellows interference to me, interfering on the side, not drooping from the top. Never have seen it on my 8x10 Dorff but its happened on the 7x17. I had to ask someone else the same question before I realized what it was.

[k_jupiter]

One of my 'dorffs has the orig. leather bellows, and they do droop. When it happens there is complete mechanical vignetting, not a 2 stop loss of exposure.
Was there pre-exposure of most of the film before the final exposure? A darkroom light leak, a holder malfunction, or user error? A bad sheet of film (I, too, use Efke, though I'm sure Arista has less problems here).
What lens and what movements?

300mm Kodak Comercial Ektar. Lots of movements (how was I suppose to know *L* ?

I would thinkedge falloff would be in a circular pattern. Perhaps not though at that image circle. I am thinking it's bellows interference from too much movement.

tim

[df cardwell]

post a picture of how the camera was set up

[SAShruby]

A spider net inside the bellows close to lensboard? I had that before...

[Alex Hawley]

[QUOTE=k_jupiter;638560]300mm Kodak Commercial Ektar. Lots of movements /QUOTE]

Tim, I use a 300 Commercial Ektar most of the time on the 810 Dorff. I've never had a problem with lens coverage except in very extreme cases of front tilt. I'm still betting on side bellows interference. The other possibility is a thin place on a bellows pleat. Have you checked the bellows for a light leak?

[Don12x20]

Test for bellows sag is similar to compendium check....

With lens open, and set at the desired aperature, look through the lens and see if you can see all four corners of the ground glass. You'll see the bellows in the path if it is there. Note that this test is easier than looking through the corners of the ground glass to see if you can see the round lens aperature - both from the physical angles (especially top two gg corners) as well as the GG seems brighter at even low light conditions than the lens opening seen from the gg...

And for your deardorf with flatbed, get some scrap pieces of mounting board, and some mounting tape. Make a bottom piece that fits on the flat board of your rail section. Put some 1/4 inch strips across this piece, separated by gaps. Now take two sections of mounting board - the width of the belows and long enough to form an upside-down V between the bellows bottom and the horizontal rail platform. Use mounting tape to tape the two as a flexible V. Now tape these to the bottom mounting board along one end only -- the other goes into one of the slots you've created.

This allows it to be collapsed when traveling, and to open up and adjust to the belows height needed (one presumes you'll have to work out the lengths but this should describe the concept.
I made one of these for sagging bellows on my Canham 12x20. Works great. Cheap. With thick mount board it lasts forever. The center discard portions of mounted work are free...if you don't do your own mounting, ask a local framing shop. IF it gets wet or dirty, make another.