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Just a few hours between road trips here, so a shorty answer tonight about altitude and UV light. Besides, Dave Cohen got all the technical stuff right-on, and there is little that anyone could add to his erudite answer other than their own experiences. The important thing here is to remember to USE FILTERS ON YOUR LENSES!!! This persistent, whining crap that I hear from railfans about "not using filters because they detract from the sharpness of your images" is mouthed by a bunch of brain-dead doofusses (is the plural of doofuss, doofi ?) who have no business giving any advice about photography that other less-informed and/or impressionable people might hear. Filters are not some gimmick devised by camera store owners to separate you from your cash--they are indispensible tools in a photographer's bag of tricks. You get what you pay for, so buy high quality filters to ensure sharpness. A high quality UV filter or 1A skylight filter will help a lot, particularly if you are shooting in open shade in higher altitudes. Personally, I like the UV filters for b&w work and the 1A for color work, as I feel that the UV filter adds a slight yellow-green cast to color photos at lower altitudes, while the 1A filter tends to render the same color balance at all altitudes. Yep, I'm lazy, and by using just the 1A filters on all of my lenses all of the time, I do not have to remember to remove them and add UV filters at higher altitudes. What are higher altitudes? Hmmm. Got me there. I suppose that one would see differences in side-by-side comparisons of railroad photos shot with and without UV or 1A filters near sea level and up on Cumbres Pass (elv. 10,015 feet), but I would bet that, otherwise, most folks could not tell the difference. The change in the amount of UV light would be gradual, being bluer in color as you increased altitude. The use of such UV or 1A filters evens-out these color differences at different altitudes. Do not use warming filters in the 81-series in an attempt to remove excess UV light, because they add a "tan" color to your image, but do not remove any UV (blue) light. But then we get into that "iffy" area of the clarity of the sky, amount of sunlight, time of day, atmospheric pollution, amount of clouds, etc., all of which will alter the color of your photos from day-to-day or even hour-to-hour. With so many variables that affect the "true" color of an image, for my money I am happy with the results achieved with just the 1A skylight filter in these "higher" altitudes. I have shot photos up in the mountains at altitudes higher than Cumbres Pass, and have noticed slightly more blue light on my slides. Was this from a deeper blue sky with less pollution or from increased UV light? Not sure, but the difference was not worth worrying about. Since there is no such thing as "color memory", you cannot look at a scene and tell how much more blue there is than at another place and time, or how much filtration to add or subtract from your lens. Your brain constantly attempts to correct this off-color balance that you see to appear as neutral, but the film cannot make such automatic adjustments. Therefore, anything you do to adjust the color balance by "eyeballing it" will be erroneous. Sure, color temperture meters can be employed, but I have found these to be tricky and not always accurate, and they do not read the amount of UV light in a scene, so they will not help you with UV. Besides, if you were to correct all color balances to be "neutral" under all lighting situations, wouldn't that be boring? Finally, with so many other differences in color balances among F-word and K-word films, variations between emulsion batches, pre-exposure storage times and temperatures, aging characteristics, inconsistant latent image storage temperatures, chemical processing variations, ad nauseum, will anyone really notice? John B. Corns Owings Mills, Maryland _____________________________________________________________________ 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 © 1998 SPORRS® - All Rights Reserved =======================================================
