P3D RBT X4 - First impressions...

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

I am continuing this series of postings with the first impressions
from using the RBT X4 camera.  Being the least expensive RBT camera
it requires some extra attention.  Remember, this is a manual camera.
No automations.  The camera does not need batteries to operate.
I decided to get this one (vs. the automated X3) because I wanted 
the lightest possible camera that takes interchangeable lenses, 
to supplement my fully automatic S1.  Also, I am hoping that the
manual operation will translate to extra reliability (remains to
be seen).  I also selected the 75 mm version because I wanted
the extra stretch of depth (again to supplement my 59mm S1)

The new RBT X4 stereo camera with the standard 35-70mm linked zoom 
lenses arrived just before my trip to Greece.  I had a chance to shoot
about 15 rolls, most of which I have mounted already.  Here are my first
impressions:

Surprise no. 1:  The camera works!!!  RBT has done a fantastic job in
linking the bodies AND the zoom lenses together.  Image size and
exposures are very well matched.  This is the number one requirement
for me in a stereo camera.  If I can detect a difference in density or
size between right and left images then that spoils the fun for me. 
And I could not see any difference in the pictures from the X4.  A
camera that passes this test (both my S1 and X4 pass) is a TRUE stereo
camera (the rest are just poor imitations :-)).

Surprise no. 2:  The lenses are decent!  I estimate the sharpness from
the 35-70mm lenses to be equivalent to a good Realist 2.8, which is
pretty good for my standards. 

Some of the positive features which are obvious or became apparent
after using the camera:

- Accurate viewfinder.  This is a distinct advantage of SLR cameras
over rangefinder cameras and it is very important IMO, especially
when using slide film.

- Interchangeable lenses with standard Pentax mount.  It is nice to 
have the option of 35-70 mm zoom but I would have been equally 
pleased if all I had were 40 mm fixed focal length lenses for this 
trip.  But I am excited especially about the use of longer lenses 
for portraits, etc.  I am already shopping for fixed Pentax lenses.

- Stereo Viewfinder:  This is an interesting concept.  It is not as
useful as some people might imagine but nice to have, to judge things
like the effect of different focal lengths on stretch and squash (try
zooming to the wide angle range... you can see the scene stretching in
the 3rd dimension.)  After using the X4 for a while I felt awkward
having to close one eye to use the S1. 

- Through the lens metering.  Useful when using filters or other
attachments.  So far the metering system appears to be accurate,
but it is a bit crude for modern standards.

- Seemingly reliable mechanical operation. During the trip I dropped 
the camera and the back popped open.  I lost a few frames from the 
resulting light leak but nothing happened to the camera (there are 
horror stories about dropping other RBT cameras).  It seems that the 
camera body can take a lot of abuse (but I'd be afraid of the thin 
mechanical links of the lenses). 

- Depth boost from the 75 mm interocular (compare with 70 mm for
Realist and 59 mm for S1.)  For subjects at 10 feet of further this is
a plus.  For close-ups it is a minus.  

- Full frame pairs and film economy:  18 full-frame stereo pairs in a
36 exp. roll (result of the 75 mm interocular spacing).  Could not do
any better than that.

How does the camera handle in the field?  

It takes some time to get used to it.  The shutter button has 3
settings:  Lightly pressed it activates the light meter.  Pressed a bit
more it lifts the left mirror only.  Fully pressed it lifts the right
mirror and fires the shutter.  I managed to work this out well by
metering and then firing quickly to move both mirrors up.  In only a
few instances the left mirror got lifted unintentionally. 

Trying to change the lens aperture without taking the eyes off the
viewfinder is rather difficult with the zoom lenses.  Zooming is a bit
easier but still a problem.  Focusing is the easiest of the three.

Two things I wished the X4 had:

- Shutter priority automatic exposure. 

- Multiple exposure capability.  

The bottom line:

The RBT X4 is a welcome addition to my stereo photography tools and I
think it nicely supplements my S1.  I like the accurate viewfinder,
through the lens metering and interchangeable lens option.  

However, it is somewhat bulky, awkward to use and it takes time to 
get good results.  Not good for spontaneous stereo or close ups or 
people photography at close range. I estimate the success rate 
(pictures kept from total shot) from the X4 at around 50-75% which
I hope will improve in the future but I don't think it will match
the S1's success rate.

In my mind, the S1 is primarily a "viewer camera" while the X4 is a
"projection & competition camera".  The extra sharpness of the S1 makes
a difference in a good viewer.  The accurate composition and extra
depth punch of the X4 will pay off in stereo projection.  As you might
know, I am heavily into stereo slide competitions so I suspect I will
be using the X4 quite a bit.  But I will always carry and use the S1
too.

George Themelis