What causes errant vignetting?

JC

What would cause my lens to errantly vignette like this?



I was at ~13000 feet, (that's Whitney ridge across the way), but wasn't freezing, I should have been well within the lens and camera tolerances.

Canon 17-40mm L. I don't usually use a CP with this lens, but I did have the polarizer on for the next series of shots, probably had it on here too, can't really remember, I think I killed quite a few brain cells here . Lens was at 17mm, but I was stopped down to F10. If it was due to the filter, wouldn't stopping down to F10 eliminate the filter ring vignetting? Or is that more a function of the focal length?

perroneford

Stopping down will not solve this. Your focal length and polarizer were the likely culprits.

ziggy53

Yes, this is almost certainly the result of using a "thick" filter on a super-wide lens, and most polarizers are pretty thick.

Consider using an oversized filter and thin step-up ring.

I don't care to use a polarizer on super-wide lenses because they generally present an uneven polarization, as in:

http://media.the-digital-picture.com/Images/Other/Circular-Polarizer-Wide-Angle.jpg

JC

ziggy53 wrote: »

Yes, this is almost certainly the result of using a "thick" filter on a super-wide lens, and most polarizers are pretty thick.

Consider using an oversized filter and thin step-up ring.

I don't care to use a polarizer on super-wide lenses because they generally present an uneven polarization, as in:

http://media.the-digital-picture.com/Images/Other/Circular-Polarizer-Wide-Angle.jpg

Thanks Ziggy, Perroneford.

Right, I usually don't use my CP on this lens, but I had it on here because the circumstances seemed to favor it, the clouds would mask the part of the sky at the largest angles from the sun, and I wanted to play with the reflections or lack thereof on the lake. The pictures I took later at a longer focal length didn't show this problem.

I do have a slim/thin UV filter for this lens (for protection, mostly), and I've never noticed the vignetting with it.

77mm has been my largest filter size, I have a few expensive filters at that size and step down rings for my smaller lenses. Good thing I don't feel the need to go for the new EF 24-70 f/2.8L II, otherwise I'd have to accept that my filter strategy was short sighted.

For some reason I thought stopping down would eliminate this problem, I guess I was wrong.

For example, 2nd shot at 29mm. You can see the gradient in the polarization between the blue sky at the top, and the cyan sky by the ridgeline, but it looks more natural seeing just the vertical sky gradient. Clouds on right mask the horizontal blue gradient you would have seen otherwise.

ziggy53

kolibri wrote: »

... For some reason I thought stopping down would eliminate this problem, I guess I was wrong.

For example, 2nd shot at 29mm. You can see the gradient in the polarization between the blue sky at the top, and the cyan sky by the ridgeline, but it looks more natural seeing just the vertical sky gradient. Clouds on right mask the horizontal blue gradient you would have seen otherwise.

Vignetting caused by internal shading certainly can be positively affected by a smaller aperture. Vignetting caused by an external obstruction, in this case the polarizer housing, will generally just get sharper with a smaller aperture, although that may allow less cropping to eliminate the affectation.