Ken Rockwell On Optical Filters
A master photographer, engineer, teacher and web publisher tells you how and why he uses traditional optical filters to create award-winning digital images!
Who is Ken Rockwell?
Ken Rockwell has been taking pictures since he was 5 years old, acquired his first 35mm SLR in 1973 at the tender age of 11, and his first of many film and digital pro Nikons in 1979. A professional engineer--he has a B.S. in Electronic Engineering and has been “studying pixels and digital imaging for over 30 years”--Rockwell has worked for such respected engineering companies as Sperry Gyroscope on Long Island, TRW LSI Products in La Jolla, California, and Tektronix in Hollywood. His pictures have been published worldwide and are held in many public and private collections. His engaging images have also garnered top awards in numerous prestigious competitions, including first place in a juried exhibition at Los Angeles’ Gallery at 777 in 1997, and at the San Diego Union Tribune’s Nature Photo Contest and 2002 Travel Photo Contest. A valued instructor and digital photography expert, Rockwell was invited to conduct a week-long workshop at the Polytechnic University of Turin, Italy in 2003, and to teach a workshop at the Yosemite Association in 2006, which will be repeated in October 2007. He has also taught a Route 66 workshop in 2006 and 2007, and is slated to do the same in 2008. Ken Rockwell’s popular photographic website www.KenRockwell.com offers a wealth of advice on how to create high quality digital images and has 1.5 million readers each month.
“In this digital age certain filters, like the color-color correction filters and the color conversion filters used with slide films, have basically gone away because in-camera auto white balance (AWB) and manual color-balance settings provide that type of control,” notes Rockwell. “However, there are still many things that in-camera settings, Photoshop, and plug-in filter systems cannot do, and that’s why I always carry traditional optical filters in my bag and use certain ones for a large percentage of my shooting. I am also lazy, which is another way of saying that I don’t like to waste time or to spend a lot of time fixing things in Photoshop when I could be out taking pictures. For example, a graduated neutral density or Color-Grad filter lets you match the subject’s extended brightness range to the more limited dynamic capture range of the DSLR sensor, so I can record both highlight and shadow detail even when the subject’s actual contrast (brightness range) is excessive. Photoshop and other post-production systems may let you achieve an acceptable looking result in such cases, but they can’t deliver highlight or shadow detail that isn’t there. I also use a UV Protector filter on all my lenses for basic physical protection—it’s a lot more sensible to replace a $30 filter that to write off a professional lens that can easily cost $1,000-1,500 or more.”
Ken Rockwell also has philosophical reasons for using optical glass filters. “I like to create the final image at the moment of exposure, “ he says. “Far too often these days people produce sharp pictures of fuzzy ideas and then try to enhance them into something meaningful in post-production. This seldom, if ever, works in purely practical terms, and there is also something to be said for the time-honored process of creating pictures in the camera as you look through the viewfinder. This is one of the prime virtues of a DSLR and people should take advantage of it. I’m certainly not against plug-in filters, and I use them myself on occasion, but there is something elegant and elemental about pressing the shutter release and preserving that magical thing that you saw and shaped with your own vision and insight.”
Filters I use, in order of how often:
1. UV Protector: I use a UV filter on each of my lenses 100% if the time, and it’s almost always a Tiffen UV Protector because they’re uncoated and therefore easier to clean in a motel sink with soap and water without damaging them. Another advantage of using Tiffen filters for physical protection is that they’re internally laminated, so they remain in one piece instead of shattering into shards when they’re broken—kind of like the safety glass in your car’s windshield. I also use multicoated UV filters on certain lenses that have flare and ghosting issues. In the days of shooting film, and when I was using the Nikon D1H and D70 I employed an 81A filter to get the warmish color rendition I prefer—especially when shooting Fuji Velvia film. However the Nikon D200 and D40 and the Canons I use today have a warmer color balance so regular Tiffen UV Protector filters work great.
2. Graduated Neutral Density (ND): I use a screw-in circular Tiffen Color-Grad ND 0.6 filter only in cases of very poor (that is excessively contrasty) light, typically when shooting a sunset. It darkens the sky by two stops, so if it’s used in ordinary light, the darker sky looks evil—great if that’s what you want, but I usually don’t. I prefer the screw-in Color-Grads in rotating mounts because they’re easy to use and are sealed from stray light. (I even use them on rangefinder cameras with external meters—I get a good exposure by opening up the lens one stop from the metered reading). The light changes very fast toward dusk and I don’t have time to mount square filters. Also, square filter holders allow light to get in behind the filter and reflect glare back onto the image from the uncoated glass filter. I have not had a problem with the fixed central location of the feathered graduation line between the light and dark areas of this type of filter—I just point the camera at the horizon and crop it later if I need to. However, orienting the Color-Grad filter precisely is critical. Unless you have a flat horizon, the filter must be rotated away from the horizontal to match the scene. If the angle is even slightly off, it looks bad!
3. Circular Polarizer: I don’t use polarizers that often, but when I do it’s mostly to amplify the contrast between a dark sky and light clouds. I also use it if I want to darken the sky regardless of whether clouds are present or not. I generally avoid polarizers with ultra-wide-angle lenses since the polarization of the sky varies with the angle and this can lead to unnatural-looking dark bands across the sky. Modern ultra-wide lenses like the Nikon 12-24mm and the Canon 10-22mm and 16-35mm L no longer have problems with vignetting when using rotating filters like circular polarizers. I therefore use a regular circular polarizer rather than spending a lot extra on ultra-thin ones. If you have any concern about this, it’s amazingly easy to test for vignetting—just shoot some photos of a clear blue sky and look at the images on your LCD. I don’t think I have to mention that the term circular polarizer does not refer to the shape of the filter—a common misconception—but to the type of polarization. Basically a circular polarizer is required when using cameras (e.g. virtually all DSLRs) that have semi-transparent mirrors in their metering or auto-focus systems. Using a linear polarizer with such cameras can result in exposure or focusing errors. Basically I use the circular polarizer because it saves me from having to select the blue sky and darken later, and I can see what I’m doing as I do it. With ultra-wides, Phiotoshop or some other post-production system may work better since it’s insensitive to the real polarization angles of the sky.
4. Once-in-a-blue moon filters: There are certain classic optical filter effects, such as the star effect that gives little starbursts at points of light in the image, fog filters in various strengths, or subtle softening filters like the Tiffen Black Pro-Mist that give a distinctive look to pictures that isn’t always easy or possible to achieve in post-production. When they’re used injudiciously the effects they produce can look contrived and gimmicky—just like bad Photoshop. However, once in a blue moon they’re just the ticket for the perfect image. Yes, you can achieve similar effects in post-production, but often they just don’t have “the look.” That’s because, for example, a star-effect filter actually relies on specular highlights to deliver its distinctive appearance and the Photoshop effects that mimic this don’t quite cut it visually. It’s also worth noting that Tiffen’s contrast and softening filters are the standard for Hollywood movies and TV—they’re one of the few makers who offer them in the huge sizes needed for $250,000 motion picture cameras. My suggestion is to have a few “once in a blue moon” filters on hand to give you certain predictable effects you may want to achieve once or twice a year. They’re all about creating your personal statement at the moment of exposure.
“Let’s face it, while optical filters provide a crucial control element in photography, finding the right place and having the patience to wait for the right moment is at least as critical as what filter you use,” Rockwell sagely observes. “That’s what defines the precise moment of exposure. People need to open their eyes—it’s not magic; just look!”
Circular Polarizer adds drama: Picture on left, shot with no filter, looks OK until you compare it with picture on right made with circular polarizer. Note darker blue sky, more emphatic clouds in polarized image. Both pictures were taken in Yosemite National Park, California with Nikon D200 and 12-24mm Nikkor lens set at 12mm. Handheld exposure for picture on left: f/8 at 1/250 sec; picture on right, 1/60 sec at f/8. Other data: +0.3 stops exposure compensation, Auto White Balance, program mode, JPG normal.
Color-Grad ND to the rescue: Lush California scenic shot without filter (left) has well-defined foreground detail, but sky looks anemic. Same picture taken with 77mm Tiffen Color Grad ND 0.6 filter shows excellent pictorial detail in sky without affecting foreground exposure. Both pictures taken in San Diego County with Canon 30D amd 17-85mm f/4-5.6 IS lens at 17mm. Exposure with no filter, 1/80 sec at f/5.6. Exposure for image at right--with 77mm filter handheld over 67mm threads of lens!--1/80 sec at f/6.3. Other data: AWB, program auto-exposure.
Filter foibles: Otherwise appealing picture of Stovepipe Dunes in Death Valley National Park, California shows unnatural bands in sky that you sometimes get when using a polarizing filter on an ultra-wide-angle lens. Picture taken with Nikon D200 and 12-24mm Nikon lens set at 12mm. Exposure data: 1/125 sec at f/5.6 handheld, ISO 100, White Balance set at “shade” to obtain a warming effect.