Zooming during an exposure.
Bhaskar
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 .
David Scarbro
> 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 ?
Nikons don't meter during exposure. Olympus is the only maker of SLR's that
I'm aware of that meter "off-the-film" during exposure.
A simple way of testing this is to meter off a dim (but not stupid subject)
at a small aperature setting (to guarantee a long exposure). Then begin the
exposure and point the camera at a bright subject.
David Scarbro
Integrated Solutions (an NBI Company)
..!nbires!fred!hds
John Hofbauer
> 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
The meter cell of the FE2 is located in the viewfinder area, so
no light will reach it during exposure because the mirror is in
the up position. Therefore the exposure must be determined before
the shutter is released. A shift of aperture during a long exposure
is less critical than during a short exposure. Reciprocity failure
makes just as much difference. Forget about the technical details,
just do it, and bracket liberally. Zooming during exposure produces
wonderful results. I've had great success with it. One was published
on the cover of a local magazine who paid me handsomely for it.
Jordan Hayes
>> is if the automatic exposure system will respond to this change by adjusting
>> the shutter speed DURING THE EXPOSURE
If you're that concerned about an aperture shift (how much of a shift
is there? More than the exposure latitude of the film? More than the
failure of reciprocity on the long exposure? How are you going to
determine the reading anyhow?), do a lot of bracketing. Is there any
other answer?
/jordan
dol...@uiucdcsb.cs.uiuc.edu
Different cameras use different schemes (eg Olympus uses off-the-film
metering, in which case the overall exposure would be adjusted, think of
it as an integration of light over time); I suggest that you experiment.
The simplest thing to do is the following: when the camera does not have
any film set the ASA to the lowest value, and take three 'fake' exposures:
one with max. focal length one with minimum and one with varying focal length.
The exposure time for a normally lit subject should be easy to monitor.
Repeat the experiment in order to get some statistical significance (read:
peace of mind that you did it right). As you may guess, the inference can
easily be made from interpolation of the time exposures!
As a final word, you may have to place in the inside of your camera
an 18% gray paper (this depends on where the light meter is located) in
order to get realistic exposure times.
Good luck!
Apostolos Dollas
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smith
> I'm aware of that meter "off-the-film" during exposure.
The Pentax LX also meters "off-the-film" during exposure.