Holger Merlitz recently tested the 12x50 Optolyth Alpins and found the exit pupil to be a mere 3,5mm. This makes them effectively 12x42s.
I have just read a report on a German forum, in which the exit pupil of the Canon 12x42 L IS WP was measured at 3,7mm. As the 10x magnification was found to be correct they are, despite their excellent optical qualities, effectively only 10x37s due to the inadequate diameter of the stabilizing prisms.
Rather than a deliberate attempt to delude their customers, I suspect however that the manufacturers have just not completed their homework - remember the "Elk Test"?
John,
Where can the Merlitz article be found?
Thanks,
Ed
John,
Prompted by a thread on Cloudy Nights, I made some measurements on the Canon and a Nikon 10x42 SE. It turns out that matters are not quite as simple as manufacturers not doing their homework properly. True, the exit pupil of the Canon is not 4.2mm wide, although it is not 3.7mm either. I got 4.0mm horizontal e.p. diameter, 3.9mm diagonal diameter and 3.8mm vertical diameter. For the Nikon, I measured 4.2mm horizontal, almost 4.2mm diagonal and only 37mm vertical diameter. These results, however, do not mean that the entire objective diameter would not be utilized. For the Canon, even with a 43mm mask covering the objective centrally, a sliver of field edge could be seen on either side. Every point of the objective lens is contributing to the image at least partially, but it seems that the very edges of the objective are not contributing to the image center. It would be just as misleading to call the Canon a 10x37 or a 10x39 when masking the aperture to those dimensions would cut out light that in the present design is contributing to the image. I'm quite sure that Canon knows what they are doing, and that the overall design compromise they have reached is a conscious and deliberate one. Anyway, the proof of the pudding is in the eating.
Kimmo