Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site tymix.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!mtuxo!drutx!ihnp4!cbosgd!ukma!psuvm.bitnet!psuvax1!burdvax!sdcrdcf!hplabs!oliveb!tymix!kanner
From: kanner@tymix.UUCP (Herb Kanner)
Newsgroups: net.rec.photo
Subject: Re: Blue tint
Message-ID: <616@tymix.UUCP>
Date: Tue, 14-Jan-86 13:42:23 EST
Article-I.D.: tymix.616
Posted: Tue Jan 14 13:42:23 1986
Date-Received: Sat, 18-Jan-86 07:15:00 EST
References: <706@hou2a.UUCP>
Reply-To: kanner@tymix.UUCP (Herb Kanner)
Organization: Tymnet Inc., Cupertino CA
Lines: 29

In article <706@hou2a.UUCP> dkw1@hou2a.UUCP (D.WOMBOUGH) writes:
>I have a question for all you netters out there. When I take pictures
>useing a electronic flash, I get a color shift, gray suits come
>out blue, and white shirts look blue .I've been told that this was
>the processings fault, but I have had the same problem with different
>Labs. Does anyone have a solution or any idea why this my be happening??
>
Two points.  First, the color temperature of flash is probably a bit blue
compared to daylight.  You can probably buy a corrective filter to
compensate for this.  Second, and I am guessing here, because I do not know
the direction of the effect, but there may be an effect due to reciprocity
law failure.  That is the the failure of a constant value of

                (light intensity) * (exposure time)

to produce a constant effect on the film for extreme cases.  By extreme
cases, I mean exposures like several seconds or 1/10000 sec.  Because the
reciprocity failure may be different in the three layers of a color film,
this can produce a color shift.  It is well-known, for instance, that a
ten-second or greater exposure on Kodachrome will tend to produce a
greenish image.  There may be something to this, because in the early days
of (non-automatic) electronic flash, 1/1200 of a second was a common flash
duration, and then, a few years later, they all gave about 1/800 sec.
However, with automatic flash, the automatic quenching when the subject is
close to the camera can give a very short exposure indeed.
--
Herb Kanner
Tymnet, Inc.
...!hplabs!oliveb!tymix!kanner