P3D Re: Twin rig exposure question

[Brian Reynolds <reynolds@xxxxxxxxx>]

Phil Palmer wrote:
> 
> I have recently finished wiring 2 XA2's together and have shot some
> colour print film for viewmagic viewing - these have come out great.
> 

I use a pair of Lubitel 166U's on a flash bar with the Olympus twin
cable release.

> Whilst messing about with the unloaded cameras in low light I have
> noticed that the shutter on one camera stays open for longer than
> the other.  With a bit of experimentation I have synchronised the
> speeds by increasing the film speed selector on one camera by two
> thirds of a stop.
> 
> Within the print film negatives I did not notice any difference in
> density - I realise print film is more tolerant to lighting
> conditions so based on the fact that I intend to shoot some slide
> film my question is
> 
> Should I keep the 2/3 of a stop difference at higher film / shutter
> speeds?  Or is it more likely that the camera light sensors are just
> a lot less accurate at low light ?
> 
> Could the cameras be in need of a battery change ?
> 
> If there is a real 2/3 stop difference in cameras am I likely to be
> able to tell when viewing the slides in a red button viewer ?
> 

How sure are you that the shutters are firing at different speeds?  Do
these cameras tell you what shutter speed and aperture is being used
for an exposure?

If you want to be sure, replace the batteries and shoot some slide
film in normal lighting conditions (daylight, open shade).  I'd
suggest using ASA 100 speed film.  Low speed film (Kodachrome 25,
etc.) might be out of the metering range of a P&S camera, and most
meters are calibrated for 100 speed film.  If you do regularly shoot
low light without a flash try some test shots under those conditions
too.

If after testing you find that one camera does need to be adjusted go
ahead and try a roll with the adjustment.  If you can tell the
difference (in a viewer or projected, however you plan on viewing
them) use the settings you like best.

With my Lubitels there is at least a one stop difference between the
shutter speeds based on looking at the slides (I haven't checked with
a densiometer).  When mounted and viewed I do not notice the
difference.

By the way, print film does not necessarily have greater latitude than
slide film.  The problem with using negative film to test exposure is
that you have to be sure that the lab does not change the exposure of
the print for each shot.  Given that most (all?) of the automated
processors in one hour labs do this, getting consistent prints for
testing exposure is more trouble than just using slide film.  With
slide film what you shot is what you get.

-- 
Brian Reynolds                  | "Humans explore the Universe with five
reynolds@xxxxxxxxx              |   senses and call the adventure science."
http://www.panix.com/~reynolds/ | - Edwin P. Hubble


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