[photo-3d] Checking & adjusting alignment by projection

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

OK, this is something new for me... Normally, I mount 
slides by checking them in the viewer.  I do not use 
alignment gauges, but just rely on the top and bottom 
edges of the mount, making sure that they intercept
homologous points.

Last night I was preparing the "Easter in Greece" stereo 
slide program, for my Greek class on Monday.  I selected
50 slides, mounted all of them in RBT mounts, put them in 
an RBT 50-slide tray and checked the tray out. I noticed
a couple of slides had a vertical alignment error. 

Definition of vertical alignment error: Even though the
frames of the mount overlap (and they stay overlapping
once the projector was adjusted for the first slide)
the R and L images show a height difference on the screen.
This difference is consistent, e.g. the L is always
higher than the R image (if that's not the case then
we have a case of rotation error).

After I approved all slides, I went back and fed each
one individually in the RBT projector, checking for
alignment.  I checked alignment by observing bright spots 
and their horizontal alignment.  Sometimes I would move
my hand in front the lenses, observing how the two
images "jump" around.  If re-adjustment is needed I
would keep a mental note, e.g. "Lower left chip".  I
would then take the slide out, open and flip the RBT
pin bar to lower the left chip.  From the total of 50 
slides, I remounted 5-6, by changing the pin bar by 
one increment (0.1mm).  

Question: What contributes to this misalignment and
why it cannot be seen in the viewer?  The problem IMO
is the fact that some times the two halves of the
RBT mount do not overlap perfectly. 0.1mm is a small
vertical step and it can be missed, but it becomes
clear in projection.

At the end of this process, I have 50 well-aligned
slides, stored in a tray.  They will project well-aligned
again and again with the RBT projector.  One advantage
of the RBT is that the lamps come on only when the slide 
is dropped in the slot.  No need to turn on and off the 
projector when checking alignment and adjusting in-between.

---

BTW, here is my new personal stereo projection setup:  

I am sitting at the kitchen table, 8 feet from the 50 in. 
screen.  The RBT projector is right behind me on the 
kitchen counter.  I hold the wired-remote to change slides 
and adjust the focus, R/L independently or both together.  
The projector is fitted with 85mm/2.8 lenses.  I got these 
lenses from ebay, brand new for $30 a piece!  They are made 
by Will-Wetzlar in Germany!  Good quality.  Leica mount.  
3 1/3" focal length. Shorter than the desirable 4" TDC 
lenses.  (I am now investigating if I could use these
lenses in a TDC projector too - stay tuned!)

This setup fills the 50 in. screen nicely and I even
turn the brightness down a bit.  My wife is watching
TV a few feet away.  The kids are playing around.
Imagine, I project and enjoy stereo slides under these
conditions!  No one is bothering me and I don't bother
anyone. I still feel I am part of this family. I hear
their conversations and I contribute too.  This was 
really unthinkable in the pre-RBT times.

George Themelis

 

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