P3D Re: 3-D Photographs of Moving Trains Problems

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Lots of good twin camera questions today...

"Darren Ferreter" <DFERRETE@xxxxxxx> writes:

>I use two 35mm cameras mounted side by side with the shutters tripped 
>by hand.  I have about a 75% success rate on fast moving trains.  
>Problem being of course,  the moving object has changed position in 
>the micro second between the two different tripped shutters.  When the 
>slides are projected, the shift in position makes for a very usual 
>resulting photograph.  The train sometimes does not appear to be on 
>the track.   

I wonder how fast is the train moving and what is the shutter
speed you are using.  The reference to "micro second" might have
been a way of saying "short time", but note that "micro" = /1,000,000, 
"milli" = 1/1,000.  Most cameras have highest speed in the order
of a millisecond and in order to see the difference in movement
in slow moving object the cameras must be off, in the order of
1/100 s or less.  Such differences would cause moving objects to
appear floating in space, but of course, the speed of these objects
is a factor too.  Actually, I am surprised at the 75% success
rate when tripping the shutters by hand... unless of course if 
in 75% of the times the trains are stopped... :-)

>I'm curious what my next step is?  Is there a better way than by 
>hand?  Would two electronic remote shutter trips be more accurate? 

Potentially, the electronic remote shutter activation can be
more accurate, but there are no warranties... It is difficult
to improve the performance by hand.  Using two combined mechanical
release cables (like the set sold by Olympus) might give you
better results.  Some of the more dedicated stereo photographers
have built electrically activated units based on relays, to trip
mechanically activated cameras.  There have been a few postings
here in the past and a couple of articles in stereo magazines.

George Themelis

PS.  As an alternative to twin cameras, consider a stereo camera.
     Don't force me to say "Stereo Realist" so let's just leave it
     to "stereo cameras" which are/were made to take synchronized 
     exposures.


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