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Filters On Filters • How Big Can I Go? • Focus On Flowers

With the Canon EF 100-400mm lens set to 200mm and a Singh-Ray Vari-ND filter, a ½-second exposure renders this rock along the California coast sharp, while the water shows movement. This image represents the outer limits of the lens’ capability to retain sharpness when working with a variable neutral-density filter.

Filters On Filters
Q I was photographing along the coast, doing studies of the surf. To lengthen the exposures, I used a Fader filter and a polarizer on my 70-200mm ƒ/2.8 lens. All the photographs from the shoot were unsharp! I practice good technique, use a tripod, lock up the mirror and usually get much better results. What happened?
H. Pati
Via the Internet

A The more pieces of glass you place between your lens and your subject, the greater the chance of degradation of image sharpness and color. For this reason, I would never advise using more than one filter at a time. The deterioration of the image is emphasized with telephoto lenses, so it’s especially important to use the highest possible quality filters on those optics. Fader filters, and other adjustable neutral-density filters, actually attain their wide range of variable neutral density by placing two polarizing filters together and rotating them to achieve cross-polarization. My colleague Vincent Laforet has tested the Faders alongside other high-end filters and found the Faders to be less sharp by comparison, but still, in his opinion, well suited for DSLR HD video capture (see Vincent’s blog at blog.vincentlaforet.com/ 2010/11/24/fader-filters/). It appears to me, however, that the difference would be quite noticeable in a still image.

In your case, you’ve added a Fader filter (actually two filters) and a third polarizing filter on a 70-200mm medium telephoto lens—thus the lack of sharpness in your captures. As a side note, I’ve used Singh-Ray’s Vari-ND filter, a variable neutral-density filter using two polarizers, for several years with excellent results up to 200mm. My advice is that the next time you want to slow down exposures to a significant degree with your 70-200mm lens, you may want to use a single ND filter with significant darkening power (3 to 5 stops) and the lowest ISO possible.

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