Late last year, I posted a blog entry about using the Fotodiox 145mm Circular Polarizing filter with the Nikon 14-24 lens. You may click here to view that entry. At that time, I owned just one Fotodiox filter. I tested the filter on the Nikon 14-24 lens at the widest focal length and noted that vignetting was not an issue.
Subsequently, I received numerous questions about whether vignetting would occur if a second filter was stacked on top of the Circular Polarizing filter. Recently, I purchased the Fotodiox ND32 filter. So, I was finally able to perform some tests regarding the vignetting with two filters stacked on the 14-24 lens. All images were captured using f/8 at ISO 100 with the Nikon D800. Here are the results:
No Filters @ 14mm (baseline)
One Filter (CPL) @ 14mm
Two Filters (CPL & ND32) @ 14mm
Clearly, the vignetting becomes a significant issue with two filters at the widest focal length. My next step was to determine the widest focal length that could be used while keeping the vignetting at an acceptable level.
Two Filters (CLP & ND32) is clean @ 24mm:
Two Filters (CPL & ND32) introduces some vignetting @ 17mm:
At 16mm, the vignetting is becoming an issue:
But, it's not all that bad @16mm after making a vignetting correction in Lightroom 4:
Vignetting is more pronounced at 15mm, of course:
But, somewhat improved after correcting for vignetting in Lightroom--especially if the image is to be cropped away from the edges at all:
Based upon these results, I will probably try to shoot at the 16mm or higher focal lengths if I ever stack two filters together on the Nikon 14-24. For most of my photography, I will only be using one filter. And, with one filter vignetting is not a concern at all.