|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?
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.
How Big Can I Go?
Q I’n a previous issue of OP, I read that a camera with a native resolution of 16 MP can make a print up to 11×16 inches. On the other hand, the instruction manual for my 12 MP Canon PowerShot SX20 says that at its largest file-size setting, prints can be made up to 16×20. Moreover, I have made 13×19 prints with the SX20 that seemed very sharp and detailed to me. How many pixels are needed for specific print sizes?
Via the Internet A It depends. First, all megapixels are not created equal. DSLRs have considerably larger sensors than compact cameras such as the Canon PowerShot SX20. When the pixels are packed onto a small sensor versus the larger one, comparatively more noise is usually the result, and that translates to less detail and color fidelity. Second, different printers offer more or less capability for quality enlargement. A multiple-function desktop printer intended for quick, small prints and text won’t produce the same quality as a printer designed for professional enlargements using a larger range of ink colors. Third, the media on which the print is made can emphasize or obscure detail and affect the acceptable print size. Finally, all photographers don’t judge the quality of a print by the same standards. These variables are at the heart of disagreement about how large a print can be made from a particular-sized file.
Twelve megapixels on any-sized sensor will produce at the highest quality setting a file of 36 megabytes (8-bit). If you print the file straight out of the camera at 300 dpi, you’ll get an image of approximately 8×10 inches. Note that some printers are optimized at 200 dpi and will make larger prints from the same-sized file. To make larger prints, we instruct our image-processing software to interpolate the file to a larger size. The software essentially fills in the spaces between the pixels as the overall image is expanded. Here’s where the size of the sensor makes a difference because each of the 12 megapixels on the DSLR sensor is larger than the 12 megapixels on the compact camera sensor, and the data gathered by those larger pixels is of higher quality. How large can you go? Stop before the file begins to fall apart, that is, where degradation of the image’s color and sharpness are noticeable. And note that some specialty interpolation software, such as onOne Software’s Perfect Resize and BenVista’s PhotoZoom Pro 4, can significantly improve the quality of your enlarged files and facilitate larger prints.
The medium you’re printing on can make a big difference in both the artistic interpretation and the acceptable enlargement size of your image. Highly textured and absorbent papers, such as watercolor stocks, soften the image. Because detail isn’t the goal in a watercolor image, you can print them larger. The rough surface of canvas also softens details and slightly mutes the colors. A sharply detailed, brightly colored rendition is best printed on a hard-surfaced, smooth medium as in a gloss or semi-gloss paper. These stocks are unforgiving; they will reveal every flaw in your image, and bigger prints only will maximize the failings.
As the creator of an image, it’s up to you to determine how your vision is best conveyed to others in the form of prints. Still, one way to educate yourself about print quality is to pay critical attention to the work of others. Look for clarity and color, and check for the telltale noise and lack of sharpness—even pixilation (jagged edges)—that say a file has been stretched to the point that it falls apart. Go to high-quality, established photographic galleries to see quality prints; an excellent example is the Tom Mangelsen “Images of Nature” galleries across the country.
|This Article Features Photo Zoom|
A spray of bush lupine is isolated from the field when photographed with a medium telephoto (Canon EF 180mm macro) set to ƒ/5.6.
Focus On Flowers
Q I really like the treatment you give to field flowers, such as poppies and tulips, where you focus on one flower or a small group of flowers with the foreground and background blurred. How do you do that?
Via the Internet
A It’s a technique called selective focus, used to emphasize one plane of sharpness in a scene. The focal length and ƒ-stop of the lens are the factors that control the range of focus and the amount and look of the blurred features in the background and/or foreground.
A telephoto lens of 200mm or longer is the tool to start with because telephoto lenses have a narrow depth of field when photographing relatively close to a subject. A wide-angle lens positioned close to the subject will fill the frame, but also will capture any background distractions quite clearly. A telephoto lens positioned to fill the frame with the same subject will be farther away, but will throw anything in the background out of focus. The longer the telephoto, the narrower the depth of field the lens maintains when used in this manner. I’ve been known to use a 500mm ƒ/4 lens to photograph individual flowers from a considerable distance in order to apply this effect. Telephoto lenses can be made to focus at a closer distance by adding an extension tube between the lens and the camera. My favorite setup for these techniques is a 100-400mm zoom with a 25mm extension tube.
Adjusting the ƒ-stop (aperture) of the lens gives you some flexibility in interpretation of the subject and the background. A smaller ƒ-stop (ƒ/8) will expand the depth of field somewhat for a larger flower or a group of flowers, but it also will begin to capture detail in the background. I often set the telephoto lens at its largest opening (e.g., ƒ/4) to minimize the depth of field and expand the unsharp area, but at this aperture, you must be certain to accurately position the sharpness on the subject you want to emphasize.
A third factor that some photographers feel is important is the shape of the lens aperture; as you stop down, the lens opening is less round, so this alters the shape of highlights of the out-of-focus background. Personally, I don’t think this is a critical factor, but some invest in very expensive lenses that maintain a completely round aperture.
In considering the composition of selective-focus images, I frequently look for foreground elements, as well as background elements, that can be thrown out of focus. This gives the image more depth, and if the foreground is very close to the lens, puts a color wash in front of the subject that leads the viewer to it.
For information about upcoming seminars and digital-imaging workshops, visit www.georgelepp.com. If you have any tips or questions, address them to: OUTDOOR PHOTOGRAPHER, Dept. TT, George Lepp, 12121 Wilshire Blvd., Suite 1200, Los Angeles, CA 90025-1176 or online at www.georgelepp.com.