A Comparison of 
Two Medium Format Stereo Viewers:

Uni-Colour International's STL vs. the SaturnSlide STL
( A Medley of Measurements and Opinions by Michael K. Davis )

Medium Format Viewer




Lens Type Glass Achromats Glass Achromats  
Lens Diameter (mm) 32 46 1
Viewable Lens Diameter  (mm) 30.5 41  
Interpupilary Distances Supported (mm) ~ 57 to 71 ~ 56 to 75 2
Lens FL (mm) 75 78 3
Magnification When Focused at Infinity 3.33x 3.21x 4
Magnification When Focused at 10 inches  - 4.21x 5
Apparent Size of 50mm Aperture with Infinity Focus (in.) 6.6 6.3  
Apparent Size of 50mm Aperture with 10-inch Focus (in.) - 8.29 6
Apparent Size of 55mm Aperture with Infinity Focus (in.) 7.2 -  
Apparent Size of 55mm Aperture with 10-inch Focus (in.) - -  
Lens Separation (mm) 64.5 65.5 7
Mount Aperture Separation (mm) 65 62 8
Mount Aperture (mm x mm) 55 x 55 50 x 50 9
Distortion with 50mm Mount Aperture Negligible Negligible  
Diffuser Density (stops) 1.2 0.6 10
Film to Diffuser Distance (mm) ~ 30 ~ 5 11
Focus Fixed at Infinity Adjustable 12
Weight (oz.) 6.1 11.1 13
Backlight Available? No Yes 14
Assembly Required? No Yes 15
Cosmetic Appeal Fair Excellent 16
Ergonomic Appeal Excellent Good 17
Current Retail Price $39.00 $225.00 18


Summary Opinion: 

Alan Lewis' SaturnSlide essentially remains unchallenged. Uni-Colour's viewer misses the mark on every count except price, the film-to-diffuser distance, no assembly required, and how it feels, both in the hands and on your nose. Smaller lenses lowered the price and increased nose comfort while simultaneously reducing the supported range of IPD's. The lower price was also achieved, in part, by using a fixed-focus design, which itself reduced the population of compatible users further still. Speaking of compatibility, if you intend to use Uni-Colour's 55mm mounts, only rubber-eyed, veteran stereo buffs can be content with more than a few minutes of the uninterrupted divergence that will be required to fuse every part of every view.  The fixed-focus design robs us of the higher magnifications we can enjoy when focused short of Infinity. The SaturnSlide's 8.29-inch apparent image size is significantly larger than 6.6 inches. Lastly, the diffuser may be far enough out to avoid visible dust problems, but it's just too dark and there's no readily purchasable light box option. The Uni-Colour viewer may be "affordable" and, certainly, ready-to-use right out of the box, but I can't recommend it except for one, limited set of circumstances: Personal use only (having tested the fixed Infinity focus and the narrow IPD range against your eyes, before purchase), with intent to use RMM mounts (to avoid the divergence problem forced by use of Uni-Colour's mounts), and the understanding that you will be sitting very close to a very bright light bulb, if not retro-fitting a home-brew light source.)  By the way, if you turn the diffuser upside down, the slot makes a snug fit for RMM mounts.  At the very least, Uni-Colour should add adjustable focus, a less dense diffuser, and an optional light box, in addition to moving their lenses out to 65.5mm and their mount's aperture separation down to 62mm, shrinking the apertures some, if necessary. A model designed specifically for RMM mounts (skinnier slot) would be nice, too. 

See these URL's for more on lens spacing vs. aperture spacing: 

Mike Davis

"SaturnSlide" is a trademark of Alan Lewis, the viewer's designer and manufacturer.
Content by Mike Davis.  HTML formatting by John Thurston