Berlin (www.imagine-your-world.com): Most photographers don’t even think about filters in today’s digital world. However, some filters are – in my opinion – absolutely necessary to get the image right in camera. These filters include graduated ND filters to deal with extreme dynamic range, a polarizing filter to increase color saturation, and strong neutral density (ND) filters. There is really nothing in Photoshop’s arsenal that can truly re-create the unique effects possible with ND filters.
While maintaining proper exposures, ND filters allow photographers to increase shutter speeds dramatically, creating motion in clouds, smoothing out rivers and rendering ocean waves as white, misty fog. Another benefit of strong ND Filters is that moving objects in an image basically disappear. A 10-stop neutral density filter reduces the amount of light hitting the camera’s sensor by about 1,000 times. It effectively blocks 99.9 percent of the incoming light, which is often overkill, especially in low-light situations. In these types of environments, a 6-stop ND-filter could be the best fit. It still blocks 98% of incoming light.
In either case, users want be able to see through the filter. This means that photographers must focus and compose the image without the ND filter on. In landscape photography, I recommend using the lowest ISO-setting available on your camera, set your aperture to the desired f-number (I prefer 9 to 11), use manual or bulb mode, a stable tripod and a cable or remote release. If your camera offers live view, use it! I also recommend locking the mirror to minimize any vibrations. Be sure to cover the viewfinder of your camera during long exposures as light can leak in, messing up the picture.
The next step is to calculate exposure times. If you use a 10-stop ND filter, you must double your shutter speed 10 times (or multiplying it by 2^10). If you are using a 6-stop filter, simply change seconds to minutes. For example, an exposure time of 1/60 sec without the filter would give you 15 sec with a 10-stop and 1 sec with a 6-stop filter. Alternatively, if you have an Android based phone or an iPhone; you can download the NDtimer app that does the calculation for you. Unfortunately, each filter is slightly different, so you have to take some test shots to work out the exact exposure.
Graduated neutral density (GND) filters are an essential tool for capturing scenes with a broad dynamic range. While grad ND effect can also be applied digitally, either during RAW development or in subsequent photo editing, I prefer dealing with a broad dynamic range on location to capture as much information in highlights and shadows as possible. Graduated neutral density filters not only capture scenes whose range of brightness exceeds the capabilities of the sensor; they also help to improve the appearance of color and detail.
Polarizing filters, on the other hand, increase color saturation and reduce glare from reflected light, which cannot be accomplished via post-processing. Most filter manufacturers including LEE, Formatt-Hitech, B+W and Singh-Ray make high-quality filters. Drop in filters allow for greater flexibility since photographers can combine several filters and adjust for the horizon. All filters increase the risk of vignetting, especially with wide angle lenses. As a general rule, filters should feature slim mounts and good coatings to avoid flare.
If you’d like to learn more about filters or just practice your skills, consider joining Imagine Your World on an upcoming workshop. The use of filters is discussed during all MasterClasses. A list of upcoming workshops is available here.