[pure-silver] Re: IR light, was.
- From: Laurence Cuffe <Laurence.Cuffe@xxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 22 Sep 2005 17:56:28 +0100
----- Original Message -----
From: Robert Hall <Robert@xxxxxxxxxxxxxx>
Date: Thursday, September 22, 2005 3:57 pm
Subject: [pure-silver] Re: IR light, was.
>
> Keep in mind that IR output from the sun is constant. Blue light is
> filtered out by atmosphere. If one has the same EV level in the
> morning as the
> afternoon, then the IR component (or content) of the light spectrum
> will be
> greater in morning and evening due to blue spectrum filtration.
>
I remember reading about someone who during the war in Gibraltar was
involved in looking across into Spain for enemy activity. One thing
they noticed was that for about five minutes before sunrise the seeing
would deteriorate before falling totaly to pieces when the sun came up.
They attributed this to the IR radiation from the sun starting to heat
the atmosphere and cause convection etc prior to the visible sunrise.
From this observation it might be interesting to do "available dark"
photography with IR film either just before sunrise or just after sunset
when the IR component, weak though it might be could constitute most of
the available light.
All the best
Laurence Cuffe
> Posing the question/statement that one has better "luck" with IR
> photographyduring these times probably means that one is using the
> light meter in the
> camera for exposure. Keep in mind that the light meter is
> calibrated for
> visible light, not for IR light. So, while the film can see the
> greateramount of IR light, the meter happily measures visible light
> causing the
> variance in exposure.
>
> Robert Hall
> www.RobertHall.com
>
>
>
>
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