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Re: Filter factors



Rolleis,

I wonder if SL filters will do the job. I have also noticed that many of my
high-altitude slides have a bluish appearance, especially at higher
altitudes. I have a couple of SL filters, but they are E-39 size and
intended for a camera whose owners do not use filters or flashes. 

Another problem may be light meters. These tend to have reduced sensitivity
in the blue and UV. This would lead to overexposure.

In any case, I am taking Marc's comment seriously. I was only joking when I
wrote that air above 5000 feet does not support life.

Best of Light

Chris

At 09:16 AM 9/8/97 -0500, you wrote:
>Hmm. How did this start ? Oh yeah, Marc's remark about high altitude and 
>UV filters.
>
>Drawing from experience gained from years shooting in Colorado, my 
>memory tainted I confess by all the coffee I've been drinking this 
>morning- UV is an enormous problem.
>
>Working with post '60s objectives [when I'm serious, I never say 
>'lenses'] which were made with Absorban or other UV Absorbing cement, UV 
>has never been a problem for me at sea level, or even in Denver, at 5280 
>plus or minus a hundred or so feet. Similar to Jo-burg or Beijing, I'm 
>told: a high prairie city. 
>
>But a thousand feet higher, and in the rural if not completely wild part 
>of the state, more deep, or higher energy, UV passes through the 
>atmosphere. Our eyes don't see it, our meters don't see it; it passes 
>through the lenses, and film loves it. The proportion of ambient light 
>comprised of deep UV is so high that overexposure is inevitable. Not 
>simple color-shift: we photograph something that the film sees but we do 
>not.
>
>Aerial shooters solved it decades ago, using UV filters that bear a 
>shocking resemblance to yellow filters. What they are, are yellow 
>filters: Wratten 2A, 2b, and 2E, etc., and they simply cut off the UV 
>light at different steps on the spectrum before it hits the lens. Some 
>cases we need to cut out blue as well, and then we shoot color through 
>filters normally used for B&W. Of course, even I figured out that at 
>some point trading UV for yellow isn't a perfect solution. So, the best 
>you can do is to use a 2A, shoot in the morning or evening when the 
>color energy is lower [shifted toward red] and when possible use chromes 
>rather than negs [on the principle that one tends to expose for 
>highlights for chromes, giving less exposure to UV than with negs.
>
>Well, that's the idea. And, of course, using these deep UV / aero 
>filters in normal shooting makes about a 2 or 3cc yellow shift, so you 
>really don't want to do that ! In short, the lenses EVERYBODY has been 
>making lately are UV proof for normal purposes, and all need help in 
>high altitude, at the beach, and in tanning booths. 
>
>But all Rollei lenses are better anyway.
>
>Don
>
>


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