Ström (strom_photo@usa.net)
Wed, 19 May 1999 22:27:25 -0400 (EDT)
In practice, I haven't found to be true the discrediting of spectral
differences between strobe and sunlight. After all, a strobe light itself may
vary according to the manufacturer of the the light and the power source,
since both are involved. Also strobe bulbs have various properties that are
advertised. I pay very little attention to these and adjust my work according
to what is available.
The film in use is possibly more important than strobe versus sunlight. I use
Tmax 100 for most of my work, but occasionally I use Tri-X professional 120
(360 ASA) or 120 Technical Pan. Technical Pan is VERY red sensitive. The
spectral sensitivities are published in Kodak's various professional film
books, but I am practical rather than preemptive. So I suffer failures.
Outdoor work with Technial Pan can be frustrating. It works fine with
strobes. I do machine develop (JOBO) and this does present problems
(Technical Pan developer for 120 will suds up and cause bels that produce
uneven negative development--an article several, maybe 10 years ago, about
development in color print developer as opposed to POTA developer would
produce negatives with a better tonal range).
Ström
Date:
Wed, 19 May 1999 17:40:02 -0700
From:
Richard Knoppow <dickburk@ix.netcom.com> | Add to Address Book |
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Subject:
Re: Indoors film speed
To:
alt-photo-process-l@sask.usask.ca
Reply-to:
alt-photo-process-l@sask.usask.ca
At 04:45 PM 5/19/99 +0000, you wrote:
>At 11:39 AM 5/19/99 -0700, Gary Miller wrote:
>>Speaking of the difference of shooting outdoors as opposed to
shooting in
>>the studio, why are the outdoors negatives so much more dense. If I
am
>>taking a meter reading both inside and outside shouldn't the
negatives
>>ultimately be the same density if I am rating the film at the same
ASA. I
>>know that Carl has mentioned the difference between using a spot
meter
>>reading outdoors as opposed to a flash meter reading in the studio.
But
>>shouldn't it all be relative? My shoots from outside are much more
dense and
>>stained than my studio shots.
>
>
>Gary,
>It's my understanding that film speeds are slower indoors typically by
a
>stop or so as compared to their rated outdoor speed. I don't know
why,
>but I'm sure that someone on the list will explain.
>
>John Erbes
>
For panchromatic emulsions the difference in speed between daylight
and
tungsten is no more than half a stop. In the days when films carried
separate daylight and tungsten ratings the tungsten rating was
typically
the next lower film speed. Ortho films will be about a full stop slower
for
tungsten light.
If you are using strobe, there should be no speed difference, at
least
due to spectral sensitivity. There may be some reciprocity failure with
some strobes which have very fast flash times. Most modern strobes have
durations of more than 1/1000sec and don't suffer from this.
If you are getting consistent gross differences in exposure indoors,
even
with tungsten light, it is more likely to be a problem with metering
than
due to the spectral characterics of the film.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
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