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From: bhaskar@cvl.UUCP (Bhaskar)
Newsgroups: net.rec.photo
Subject: Zooming during an exposure.
Message-ID: <1278@cvl.UUCP>
Date: Wed, 5-Mar-86 13:22:07 EST
Article-I.D.: cvl.1278
Posted: Wed Mar  5 13:22:07 1986
Date-Received: Fri, 7-Mar-86 08:27:59 EST
Distribution: net
Organization: Center for Automation Research, U. of MD, College Park
Lines: 33

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  I have a question regarding the use of a zoom lens and hope that somebody
will be able to help me. I have consulted my camera manual, and the zoom 
lens manual as well as most of the books on photography I found in the
libraries on campus - but still came up empty. So here goes :

  The zoom lens in question is a Vivitar 70-210mm f/2.8-4.0 Series 1 lens 
and the camera is a Nikon FE2. I am planning to zoom during an exposure  
at dusk, with the camera set on automatic (aperture priority) mode. 
  
  During the zoom the effective aperture of this lens changes. My question
is if the automatic exposure system will respond to this change by adjusting 
the shutter speed DURING THE EXPOSURE - the shutter has already been released
and the exposure is in progress when the aperture changes because of the
effect of zooming with this lens. Does the metering system select a shutter
speed at the instant  the shutter release is depressed and "freeze" it for the
duration of the exposure ? Or does the system respond to changes during the
exposure ?

  I am concerned about this because I expect the exposure to be fairly long.
If the exposure was short, a decrease in aperture during the exposure would
probably not have any significant effect. For all I know, there may be no
significant effect even during a long exposure - I have still not made the
exposure I had in mind. Perhaps the best thing is to expose in manual mode
for a "mean value" aperture between 2.8 and 4.0 and bracket around it.
But I would still like to KNOW WHAT HAPPENS !

I hope this is clear enough to be comprehensible .