Polarizing filters absorb just 1-1/3 stops of light, but their effect on film can cause your exposure to change by more than that amount. Be sure that your TTL reflected-light meter is not fooled by this now dark-looking subject, and does not tell you to open up the f/stop to the point of over-exposure. On the other hand, your hand-held incident light meter will not be affected by the polarizing filter on your lens, and you must compensate for the filter manually on the camera, as well as any purposeful extra exposure to compensate for the newly-darkened subject. By removing the lighter, reflected light with a polarizing filter and allowing the darker color of the subject to show up, you might have to open up your exposure somewhat in order to get more detail into this now dark-looking subject.
By the way, polarizing filters are actually clear in color--they look gray because they absorb 1-1/3 f/stops of light as we look at them. There are two types of polarizing filters--linear and circular. Some newer cameras with "auto-everything" systems need the circular type for proper operation, but either type will remove refections from your subject. You can hold a pola filter up to your eye and rotate it around an arc of 90-degrees to see the affect that it will have on any reflections of your subject and the sky behind your subject. Take a look first before screwing the filter onto your lens, as there may be little or no effect, and you may not need it after all. Polarizing filters remove different reflections at different angles--a pola filter that has been turned in order to remove reflections off the horizontal surface of a lake will not remove reflections off the vertical side of a diesel without being rotated 45-degrees in either direction. Once rotated to remove the diesel's reflections, the reflections in the lake show up again. Polarizing filters cannot remove reflections from shiny bare-metal surfaces or mirrors. Polarizing filters will give you darker blue skies behind your subject, especially when the blue sky is at a 90-degree angle to the axis of the sun (the area of darkest blue sky on any blue-sky day). Knowing this, you can see how the time of day can affect the amount of blue sky you will get behind your subject relative to the sun's position in the sky. A high-noon sun will put the bluest part of the sky in an arc lower toward the horizon, while an early-morning or late-afternoon sun will place the bluest sky in overhead arc like the St. Louis arch. If you want blue sky in your photos, plan your photos of stationary subjects based on the time of day and their orientation to the sun, and shoot them when the sun angle is best for the blue sky. Use the pola filter to darken this bluest part of the sky. How do you find a 90-degree angle to the axis of the sun as mentioned in the last paragraph? Make a "gun" out of you thumb and index finger, and "aim" your index finger toward the sun. Now, rotate your hand and wrist around the axis of your index finger, and your extended thumb (which is at a 90-degree angle to your index finger) will point to the area of darkest blue light. Play with this "gun" to see where the darkest blue light will be with the sun in different positions based on the time of day. See how the area of blue light changes? Maybe that photo of the white Soo Line diesel that you had planned to shoot in the morning would look better at noon when the blue sky is darker behind it. Just for fun, place one polarizing filter over another, rotate it, and see what happens. You can do this to get a neutral density filter with a LOT of density! But color films will take on an extreme color shift when your exposure is increased by this much. (Sorry, I no longer remember how many stops this is, but it is NOT 2-2/3 more stops!!!) With black steam locomotives, you can "over" polarize the boiler refelections to the point of making the clyindrical boiler look like a flat plane due to the lack of reflections which tell our brains that the object is curved. Foliage reflects light from the sky, so the leaves look washed out without a pola filter. On blue-sky days the leaves reflect blue, which de-saturates their green color. In the fall, yellow leaves (or orange or red leaves) reflect blue sky, and are de-saturated in color. Want great fall colors? Use a polarizing filter. Want spectacular fall colors? Use the pola filter at the correct time of day to get the best blue sky behind the leaves. How you get the train to show up at that very moment is your business! John B. Corns _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866] -> SPORRS: Serious Photographers of Railroad Related Subjects -> Web Site: http://www.anet-stl.com/acphotog/sporrs -> Message © SPORRS® 1998 - All Rights Reserved
