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Thursday, November 1, 2007

Best Polarizer Techniques

A Polarizing Topic • Digital Duping Vs. Scanning Standards? • Cheaper Presentations

tech tips polarize
These two images were captured in a Kansas sunflower field. The one on the left was taken with a polarizer, the one on the right without a polarizer.
A Polarizing Topic

Most of the time, I leave my polarizer on the lens. I’ve been told that isn’t a good idea. When should I have it on and when should it be stored away?
H. Howell
Atlanta, Georgia

There’s no doubt that a quality polarizer can make all the difference in the outcome of your images in many situations. The most common use in landscape photography is to darken the sky and remove reflections from water. But anything you put over your lens will degrade your image quality slightly. The biggest problem with using a polarizing filter when you don’t need one is the loss of light—at least two stops. That means you’re being forced to use a slower shutter speed than you might want to (as in bird or wildlife photography) or a larger ƒ-stop that keeps you from achieving the depth of field you need (as in macro flower photography).

On the other hand, the polarizer can be used as a neutral-density filter, allowing you to choose a longer exposure when you want to slow down water for effect. There’s another benefit to using a polarizer. Often, vegetation reflects a sheen from a bright sky, masking the saturated greens we expect from the foliage. A polarizer brings back the brilliant colors.

Before you use the polarizer, check to see if a desirable effect can be achieved by holding it up and rotating it before your eyes. Make sure you look through the polarizer in the same direction your lens would.

The short rule is to use the polarizer when you want to eliminate reflection, deepen a bright sky or slow exposure times. Otherwise, you should leave it in the bag.

Digital Duping Vs. Scanning

I’m about to start converting thousands of old slides to digital. I'm looking at the Nikon V ED 35mm film scanner. I recall an article in the October '06 issue about duping slides with a D-SLR with an accessory that attaches to a camera lens. I’d use a 12-megapixel D-SLR to do this. Will the slide duplicator on the digital camera give me the same quality as the Nikon V ED film scanner? I'm on a budget, but I’m willing to spend the money on a dedicated film scanner if the quality is that much better.
J. Perry
Santa Maria, California

If you want to get the very best quality possible from your film-based images, the answer is a film scanner, and the Nikon Coolscan V ED or Nikon Super Coolscan 5000 ED are excellent choices. The duplicating method you mention with a D-SLR would be more than adequate if the images will be used only for the Internet or small prints. You'll get a higher-resolution file from the scanner, and you'd need this for high-quality prints. But the advantage of the film scanners are that a number of corrections can be made to the scan as it's initiated. Either individually or for a set of similar images, you can adjust the scan to correct color, contrast and exposure.

The Nikon scanners also have the advantage of eliminating any dust spots that may be present on the slides. It's almost impossible to get a slide perfectly clean, but the Nikon scanners add a scanning function (Digital ICE) that identifies debris on the surface of the image and masks those artifacts in the final file.

Considering the labor involved with either method, I suggest you do what you can to get the best possible file from your slides. That would mean the scanner.


When I switched to digital photography, I was anxious to preserve my investment in lenses and accessories. So I cleverly bought a Konica-Minolta camera just days before they announced they were selling out to Sony. The K-M RAW file format has become instantly obsolete, and I wonder how long it will continue to enjoy support in Photoshop and other image-processing programs. My immediate solution has been to convert the camera's output into Adobe DNG format, but there’s no assurance it will last forever, either. What do you think?
R. Baker
via the Internet

Standards are difficult to establish when technology in a field moves as fast as it is right now in photography. Your particular circumstance is a perfect example of the problems caused by limited backward compatibility in photographic file formats. Your use of the Adobe DNG format is the best answer at the moment, but it also may be temporary. At present, I save all my images in their original RAW format, as a DNG and, if processed in Photoshop, as a PSD.

Also, be careful of the media on which your images are being stored. CDs continue to be accessible, but they're being overtaken by DVDs and HD DVDs, and Blu-ray, and who knows what’s next? I once lost a number of images stored on magnetic optical disks proprietary to IBM. Once my disk reader failed, I could find no reasonable way to recover the images, which probably weren’t worth it anyway, considering that the scans were performed at low levels and the file sizes involved were too small to be usable now. In other words, the work was lost in technology that was no longer viable.

Those of us working within the new technologies must be ever vigilant to protect our images from becoming obsolete because they’re encapsulated in obsolete formats or storage devices. This means that if you’re serious about your work, you'll move it from one format and storage system to another in a timely fashion. Don’t wait for too many generations, or your opportunity may be lost, along with your work.

Much as we bemoan this continuing problem, we need to celebrate the benefit of new technology that gives us opportunities and tools to achieve quality we’ve never been able to approach before. However, that, too, creates a different critical environment in which to evaluate our older work and that of others. It’s all part of the progression of the art and technology of photography and, despite the problems, I love being part of it.

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