Tuesday, April 26, 2011
Filters On Filters • How Big Can I Go? • Focus On Flowers
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?
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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