I have the Pentax PCF WP II 12x50mm
and the Pentax PCF WP 16x60mm
& the Pentax PCF WP II 20x60mm
All three are excellnet Porro prism binoculars and rugged & higher quality than many of the Porro prism binoculars on the market in that price range.
As you stated, the Nikon AE ATB 12x50mm is multi-coated, and the Pentax is Fully Multi-Coated, my own personal comparison between the two showed the Pentax to be brighter & clearer. (better light transmission due to the up-graded optical coatings?)
The Pentax PCF WP II has what is called Inner-Focus Optical Design which gives a JIS Class 6 Waterproofing to this series of binoculars. The Nikon AE ATB binocular does NOT specify what rating of waterproofness has been tested for that particular model.
The Pentax comes with very long Eye Relief, 20mm, which is important for eye glass wearers.
The Pentax comes with a Focus Lock, you can set it and forget it.
Balance in my hands with any one of the three has always been excellent for hand holding.
The Nikon is soft at the edges, and the Pentax is sharp to the edges, which to me offsets the smaller FOV of the Pentax.
The Pentax would be better for stargazing because of the sharpness out to the edges.
I have had no problems with ghosting or internal reflections when stargazing, while using the Pentax 12x & 20x WP II models. The discontinued PCF WP 16x60mm has older optical coatings, which do show minor ghosting on very bright targets such as a full moon.
If you hand hold the 12x from a comfortable sitting position you will do well, otherwise a small, lightweight tripod is preferable, or even a monopod.
Edited by Bird Watcher - August/23/2009 at 08:23