Just to resurrect an old thread I was looking at the difference between old 12x36 IS and newer 12x36 IS II models.
As the technical detail are missing from above discussion and you can find them on the Canon USA website I summarize them below for the optical geek
old 12x36 IS
http://www.usa.canon.com/consumer/c...lTechSpecsTabAct&fcategoryid=128&modelid=8167
newer 12x36 IS II
http://www.usa.canon.com/consumer/c...lTechSpecsTabAct&fcategoryid=128&modelid=9836
The older 12x36 IS:
uses a roof prism for image inversion rather than porro 2 prism
uses a more complex eyepiece (7 elements in 5 groups versus 5 elements in 4 groups) with a bigger 67 degrees versus 60 degree AFOV and a little more ER (15mm vs 14.5mm).
bigger AFOV leads to a bigger FOV (at the same magnification).
has a closer Closest Focusing Distance of 3.7 meters/12.1 feet rather than 6 meters/19.7 feet on the IS II
has older stabilization system with a smaller stabilization angle of 0.7 degrees versus 0.8 degrees. I wouldn't be surprised if other parts of the IS system hardware and software are different and the newer ones perform a bit better.
can use 43mm photographic filters in front of the objectives (for polarized filters, or color or neutral filters or even just UV or clear filters to protect the objective from dust ingress or damage or fingerprints. The newer one can't use filters (this is a loss).
has a smaller IPD range (60 to 70mm) than the newer IS II (55 - 75mm)
is heavier (without batteries but that's the same for both) at 890g/31.4 oz than the newer IS II 660g/23.3 oz
is bulkier versus 169 x 141 x 73mm/6.7 x 5.6 x 2.9 in. versus 127 x 174 x 70mm/5.0 x 6.9 x 2.8 in.
So it's a mixture. The filter feature was lost, EPs simplified reducing AFOV and FOV and close focus moves out whilst the bin gets smaller and lighter and perhaps has a better IS system.
Optically I suspect the porro 2 should beat the roof (just because it's much easier to get the latter right) but it would be nice to do a side by side comparison. Though I wonder if the EP design has a ED/UD/LaK element that was dropped in later design.
I believe the newer IS II shares it's EP design and it's porro 2 inversion system with the other more recent 3mm exit pupil IS bins. Rather like the Nikon SE family with a constant exit pupil and identical EPs.
I note on eBay the wrong pictures are used all the time. The original IS is more boxy with the EPs lower down. The newer IS II is more round with the EPs sticking up higher.
Old one
http://www.usa.canon.com/app/images/binocular/12x36is_586x225.jpg
New one
http://www.usa.canon.com/app/images/binocular/12x36isii_586x225.jpg
The obvious field mark is the button which is medial in the new design but offset on the right barrel in the old design.