Re: Sawyer Bi-Lens viewer ghosting

[P3D Michael Watters <mwatters@xxxxxxxxxxxxx>]

The ghosting is NOT caused by coating problems.   The ghosting is a problem inherant to  
the design.   The image is initially split by a beam-splitter (ie a REAL beam-splitter,  
partially silvered mirror that reflects 50% and transmits 50%).   Now, when the light first hits  
the beamsplitter it hits the mirror and reflects SOME and the rest goes into the glass of the  
beam-splitter (exiting to be sent to the other eye).  Anyway, it's the exiting from the  
backside of the beamsplitter that causes the problem.  Even though it isn't silvered, you  
get SOME reflections just because of the transition of light from the glass to the air.  (BTW  
This is EXACTLY why diamonds sparkle and why your rear surface bathroom mirror will  
give ghost images too...  The front side of the mirror reflects a little even though it isn't  
silvered.  That's also why good quality optical mirrors are FRONT silvered.  Can't do that  
with a beam-splitter though)

The actual mirrors in the bi-lens are front surface and pretty good.

My experience with it has been very good.  I've only noticed the ghosting on images with  
strong contrast (night shots of lights and such).

As long as the price is right (I've never paid more than $5 for one) they are a great viewer  
and my choice for viewing flat 2x2 slides.

mike
watters


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