From: Sandy King (sanking@clemson.edu)
Date: 12/12/01-01:43:37 AM Z
John,
>
>Assuming that you are correct about the inverse square not being applicable
>to linear source light (and I'm still not convinced that this follows
>logically-a line is an arrangement of points, yes? and filtered, to boot!),
>the question remains: Is there any evidence of banding due to proximity of
>negative and print to the light source?
People certainly have reported banding. Dick Arentz, for example,
warns against it in his book on platinum printing and he is one of
the most technically proficient printers working today. However, I
never experienced it working with my UV bank with very close (1/4")
spacing. On the other hand I am sure that at some tube spacing (2",
4" 6"?) you would see banding.
>
>And a second question occurs to me: Is there a predictable behavior (sorry,
>I'm trained as a shrink) for light that is not point-sourced? A
>correspondent to the inverse square rule, perhaps?
Did you read the previous message from Richard Koolis?
>
>And might there be other variables not accounted for?
>
>I'm not blindly argumentative here. My reasoning is that the inverse square
>behavior is useful to astronomers, etc. who are observing phenomena not that
>unlike a fluorescent tube. Cosmological point sources (i.e., stars) are
>filtration devices, with atmospheric influences which defuse the source
>radiance.
>Right?
All stars are point source lights, no question.
>
>And does the inverse square not apply out from the filter? Is there a
>compounded inverse square as affected by some rate or factor of diffusion?
>(Assuming that all diffusers are not equal.)
>
>--> Is there any banding? That's the question.
>
>And what did you think of Beth Daniels?
I like Beth. She is a good colleague and friend! You think she might
know something about the inverse square law and/or banding?
Regards,
Sandy
>
>--John
>
>www.photogecko.com
>
>
>-----Original Message-----
>From: Sandy King [mailto:sanking@clemson.edu]
>Sent: Tuesday, December 11, 2001 10:21 PM
>To: alt-photo-process-l@skyway.usask.ca
>Subject: Re: uv ballast ground, yes
>
>Anyone with a UV bank of fluorescent tubes and a step wedge can
>easily verify that the inverse square law does not apply when
>exposing with such a unit. You can easily test the premise.
>
>Using whatever process you are familiar make one exposure of the step
>wedge with the tubes at at 2" from the exposing plane. Assume that
>the exposure is 20 seconds. Develop and process the step wedge and
>note the first step that gives you maximum density. Now make another
>another exposure with the tubes at 4" from the exposing plane. Apply
>a correction for time assuming that the inverse square law applies
>and give 4X the first exposure, or 80 seconds. Develop and process
>the second step wedge. For the inverse square law to apply both step
>wedges should record the first maximum density on the same step of
>the wedge, after exposure and processing. They will not. The step
>wedge that received the 80 second exposure will be very much
>overexposed when compared to the one that received 20 seconds.
>
>There is no magic here. The inverse square law only applies to light
>rays diverging from a common point, as with a point source light. In
>a UV bank of tubes the total amount of radiation that falls on the
>exposing plane is a combination of rays: point source, near parallel,
>and rays intermediary between the two. The inverse square law only
>applies to those rays which emanate from a common point, not to the
>near parallel and intermediary rays.
>
>
>Sandy King
>
>
>
>
>> >light has no "choice" but to obey the laws of physics, that
>>>includes the inverse square law. Light is not magic, it can and must be
>>>described in a rational way.
>>
>>I am puzzled by the explanation why the square inversion law should not
>>apply for the bank of lights, and I'm too not convinced that this is
>>true, but on the other hand light IS magic. Funny things happen to it
>>(although on a different scale). If you are curious and have a moment to
> >spare please read a very short book by Richard Feynman: "QED - The
>>Strange Theory of Light and Matter".
>>Have fun.
>>Ben
>
>
>--
--
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