47 SA XL vignetting on my Ebony SV45U

[Jan Becket]

I found I needed wider coverage than my 75 Grandagon offers and sprung for a 47 Super Angulon XL and the corresponding center filter. My Ebony is advertised as able to mount a 47 SA XL, but I have tried numerous configurations and still get vignetting in the corners, about 1/4 to 1/2 inch. I cannot seem to get a full 4X5 neg. This is strange because I came up with a method of focusing that involves a small LED flashlight placed 6 or 8 feet away. That makes it possible to focus accurately and then to check that the point of light appears in each of the 4 corners. However, the fact that the light appears does not seem to indicate that there will not be vignetting, as in a totally clear corner, no exposure. Weird.

I just concluded (another) test in which I
1) Set the asymetrical rear tilt to the max
2) Raised and tilted the lens on the front standard to make it parallel with the rear standard and centered
3) Used the LED flashlight to focus (8 feet, f/16 @ 1 sec)
4) Removed the rear ground glass to check that the bellows is not blocking the rear element of the lens (which it can do sometimes)

I see that I could somewhat balance the corner vignetting, since the lower corners on the image have more than the upper ones. This means lowering the front standard - I think. However, there will still be some vignetting in all corners. I have previously tried the standard rear tilt rather than the asymetrical rear tilt, and have tried a combination of the two. I called Bruce at Badger Graphic Sales, where I purchased the Ebony, but he could not offer specific advice, and commented that 47 SA XL lenses can have varying coverage. Anyone else run into that issue?

Iʻve used 4X5 for 30 years and have a book out - I have the feeling that I should be able figure this out. Or maybe not. This is beginning to remind me of when I first started and needed to figure out where in the film holder to place those notches ...