RE: Autoexposure Follies? (was Re: Nikon Data Backs

[Theo Benson <TBenson@xxxxxxxxxxxxx>]

Good point about the deceptive subjects. You are so right! I've had standing
water completely absorb IR one day, and completely reflect it the next. Just
depends upon the angle of sun, I guess.

I plan to run a test using my 87C filter and my N90s internal light meter to
see if I can't come up with some kind of compensation number. I know the
meter is sensitive to IR, it just isn't calibrated for it. I'll let everyone
know what I come up with.

> -----Original Message-----
> From:	Joshua_Putnam [SMTP:josh@xxxxxxxxxxxx]
> Sent:	Tuesday, July 14, 1998 3:45 PM
> To:	INFRARED@xxxxx
> Subject:	Re: Autoexposure Follies? (was Re: Nikon Data Backs
> 
> pico <pico@xxxxxxxxxxxxxxxxxxxx> writes:
> 
> >All this talk about the difficulty of using a modern, highly
> >advanced camera for IR seems to indicate that it's simply not a
> >good choice, and perhaps a totally manual, nonelectric, simple
> >camera would be best. Perhaps an old Nikon F, Leica M, Olympus,
> >Koni-Omega 6x7, etc...
> >
> >This _assumes_ that integrated meters cannot really be set
> >properly for IR work. 
> 
> While I'll still bracket under difficult conditions, or for
> shots that would be hard to re-take if the first try doesn't
> work, I actually get fairly good exposures for both HIE and
> Konica using auto-exposure on my OM-2 and OM-4, metering through
> a no.25 filter in bright to fairly hazy conditions.  The
> exposures may not be absolutely perfect, but I get only one or
> two really useless negatives per roll.  (Of course, that's
> partly because HIE gives interesting effects over a wide range
> of exposures, so I may end up with a useful negative that isn't
> what I was planning on.)  I just set the film speed dial to 400
> and shoot.
> 
> Usually the really useless negatives are with HIE, from subjects
> that are dramatically more reflective in IR than deep visible
> red.  The slag heap of a local copper smelter comes to mind --
> in visible light the rock appears dark brown, almost black, but
> it's almost as bright as tree bark in IR.  Where the tide ranges
> over it, it's covered by a dark slimy seaweed that is also
> fairly bright in IR.  Anything shot auto-exposed at 400 against
> that background will give a negative so dense you'd think the
> film had been directly exposed to daylight.  
> 
> With an 87 over the lens, my OM-4 does get something registering
> on the meter, but I haven't taken the time to attempt to get a
> good film speed setting for auto exposure.  (The meter on the
> OM-4 is separately lit from the viewfinder, unlike the OM-2, so
> it is possible to see what reading it's getting even though the
> viewfinder is completely black with the 87 in place.)
> 
> I have not tried any auto-exposure using the between-the-rails
> filter -- I assume the auto exposure would vary wildly since the
> meter would be seeing all the light, not just what gets through
> the filter.  (Besides, right now I have the between-the-rails
> filter on my OM-1, so auto anything isn't an option.)
> 
> -- 
> 
>  Josh@xxxxxxxxxxxx  is  Joshua Putnam / P.O. Box 13220 / Burton, WA 98013
>                        "My other bike is a car."                   
>                      http://www.wolfenet.com/~josh/
> *
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