To Warren and others with inquiring minds-- I am reposting part of my SPORS message from 2/14/98 about the area of the sky with the bluest light, and will comment some more after that about Warren's questions.
>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. Is this the relationship between sun and lens that you were thinking of, Warren? As you see, the deepest blue color will be found at a 90-degree angle to the axis of the sun, regardless of which way the camera is pointing. At times with a wide angle lens it is possible to see the arc of blue light arching up through the sky, while the remainder of the sky was a lighter shade of blue. The time of day changes this arc of blue light--the extremes being the sun directly overhead (like at the equator) with the arc of blue light completely around the horizon and lighter blue sky high above, and the other extreme with the sun at the horizon with the arc of blue light like a wide ribbon arching overhead like the St. Louis arch as mentioned earlier. I think this is what Warren was referring to with his mention of 90-degree angles to the axis. The pola filter just makes these arcs of blue light deeper in color by removing reflections of particles in the air at that 90-degree angle to the sun. Knowing this, if you want the deepest blue sky behind the clock tower of union station as you look up at it from close by, shoot the photo in the early morning or late afternoon in order to catch this deep blue sky at its highest point in the sky. This is kind of complicated to explain verbally without drawn diagrams to show you where these areas of deep blue sky are located in relation to the ever-moving sun. Hope this explains it. Questions? Just ask. 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
