P3D Re: 3-D Photographs of Moving Trains Problems

[George Gioumousis <georggms@xxxxxxxxxx>]

Dr. George A. Themelis wrote
> 
> 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.
> 
> 
If the two cameras are SLR's (with focal plane shutters) there is another
sort of distortion even if the two shutters are synced pretty well. I
well remember elliptical bicycle wheels.

George G.


------------------------------