P3D Viewing with vs. without lenses

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

OK, it seems that most people think that if you don't use
any lenses you don't have any magnification.  Hence the
term "zero magnification".  But the main purpose of the
lenses it to see a clear image with relaxed eyes at a short
distance.  Stick a picture at 2 inches from your eyes.  
All you will see is a blur.  Put a 2 inch (50 mm) focal
length lens and you will see a clear image.  That's what
the lens is for.  Not necessarily to magnify. 

By convention, the magnification is one "1" when the viewing
distance is 250mm.  So even if you don't use lenses you can
get magnifications higher, lower, or equal to one.

The term stretch indicates a mismatch between the recording
and viewing distances.  You don't need lenses to experience
stretch.  As a matter of fact, chances are that you are
viewing from further away if you are not using lenses
and so you experience more stretch (try moving a stereo
view further away as you freeview... don't you "see" more
depth?  That's what we call "stretch")

I know many people enjoy freeviewing stereo prints and
claim that this viewing method has many advantages...
"zero magnification", no stretch, no chromatic aberration,
no distortion due to the lens, etc.  Freeviewing has one
big advantage:  You don't depend on a device to see
stereo.  But if you have a viewer on hand, why would you
freeview? 

IMO there are two main reasons that people enjoy freeviewing:  

1) They cannot see details, hence the image looks sharp 
(have you tried to use lenses to view stereo pairs in the 
computer monitor?  what a difference!)  

2) They like the stretch, a result from viewing the image 
from too far away.  Seeing the image at higher magnification
with a viewer usually results in a disappointment when the
stretch goes out of the window.

So, if you want to see sharp images with exaggerated distances
in the z-direction, freeview.  If you want to see details and
judge sharpness, use a viewer.  IMO, a "bad" (unsharp, not 
much depth) stereo picture looks better when freeviewed.  
A "good" stereo picture looks fantastic in a good viewer where 
all the glorious details are seen.

George Themelis