One big advantage of digital images is the ease and amount of after-shot manipulation one can do. This and in-camera
white balance can replace the need for many filters on the camera. There are, nevertheless, a few filters that camera controls
and image editors will continue to have a hard time replacing. These are filters that are highly dependent on the range, direction,
type, and intensity of actual light in the scene, not what's left in the saturated, final image.
Polarizer
A polarizer is the staple of most outdoor photographers' filter diet. If you want big sky or intelligible shots of or through
reflective surfaces, you must have this filter in your bag of tricks. PhotoShop and the like are really poor or impossible
substitutes for these effects. You rotate the filter to achieve the maximum or desired degree of polarization.
Outside, the polarizer is most effective when pointing at right angles to the sun and the higher you aim, the deeper the
blue. Sunlit clouds, trees and buildings really start to pop dramatically. In the morning after a nice storm you can turn
the sky almost black at certain angles and exposures. At other angles or near the horizon, it might have little effect, but
you quickly learn when not to bother.
Sometimes you want heavy reflections when shooting through a window. Sometimes you don't and only a polarizer can help
you there. PhotoShop cannot reveal the detail behind the reflection. In color or black and white, the polarizer can. Likewise,
any shiny surface can include undesirable reflections or glare. A properly rotated polarizer can wipe them out like magic.
Soft Effect
There are a few other things you might want to do to the light before the camera other than polarizing it. If you do portraits,
consider an optical quality soft effect filter for your next purchase. The good ones blend the lighting for a kind of misty
or halo effect without degrading the focus. This generally reduces contrast but adds tonal gradations and ultimately smooths
out blemishes. Even landscapes can take on a more romantic tone. The finest I have seen are the Hasselblad Softars, which
come in 3 grades. They look like clear glass with fairly large beads of rain on them. The most common ones from other makers
such as Tiffen (which also come in grades) look like finer wavy ripples as if the rain has been blown across the glass in
a strong wind.
I have only found one obscure photo editor that even comes close to this effect. Most, including PhotoShop, degrade the
entire image sharpness. If you want sharp but not harsh renditions, a filter is your only hope because it works with part
of the light on the scene while allowing image sharpness to be maintained as usual with the rest of the light. In stronger
or contrasty light, a halo effect can be achieved. Processing a final, saturated image cannot match this romantic effect with
the quality of a real filter.
A number of variations on this theme exist that I have not tried. They include fog effects, color tinted versions, and
light or dark meshes, but a standard one will probably be more generally useful -- especially in portraits.
Special Effects
After acquiring a polarizer and a soft effect filter, you might want to delve further into the world of special effects.
If you can use a common filter size such as 52 or 55mm, there are enough goodies out there to make your head spin. As the
term "special" implies, these are a little more esoteric and not for everyday use. Their effects, however, are often so dramatic
that you might feel them cost-justified after only a few uses.
My personal favorite is the crosstar filter. Specular highlights (the real intense ones) burst into a cross of various
sizes depending on your aperture and the highlight size. Poor man's versions can easily be made with a piece of window screen,
but the optical varieties are much cleaner and available in 4-point, 6-point and even 8-point varieties. A window screen can
actually produce both soft focus and star effects simultaneously. The optical ones are designed to minimize the softening
while producing fine stars. Variations on this theme include diffraction gratings (rayburst) which produce rainbow colored
bursts.
Really Special Effects
Finally, something really specialized. Just below the visible light part of the energy spectrum (shorter wavelengths) is
ultraviolet. Just above (longer wavelengths) is infrared. Although they are designed for visible light, many digitals are
also somewhat sensitive to infrared. Simply block out visible light while passing infrared and you expose a world we never
see with our own eyes. Greenery is much brighter in infrared while open sky is much darker for example.
Completely opaque infrared filters can be very expensive, but near infrared, which lets in a little visible light, is enough
for really dramatic effects while avoiding extremely long exposures. For digitals, the Hoya R72 (Wratten 89b equivalent) is
the only one I can recommend. It is affordable at around $30 and permits reasonable exposure times. A tripod is an essential
companion device if you decide to try your hand at infrared because exposure times even in bright sunlight with the R72 will
likely be one second or more.
Caution: Infrared sensitivity may be cut off in some cameras, in which case no filter will give you a usable image. You
can test your camera with a standard infrared TV remote. Point the camera at its emitter while viewing the LCD viewfinder.
If the emitter lights up when you press a button on the remote, you have some infrared sensitivity.
