Binoculars - Restricted Exit Pupils

[John]

In the latest issue of Astronomy Now they review 7 pairs of 10x50 binoculars ranging from £25 to £120. What really suprised me was that in many cases the measured exit pupil was smaller than it should have been (5mm). In one case (not the cheapest) it was as low as 3.9mm which aparrently equates to a light loss of 39% !. Only 2 pairs offered the full 5mm.

Surely in this day and age of informed consumers we should be entitled to know if a pair of binoculars is actually stopped down in some way - ie: it should be clearly marked on the packaging and published specs rather than having to find a review where the actual exit pupil has been measured ?. In the worst case sample tested you were effectivly buying 10x40 binoculars rather than the 10x50's they purported to be.

John.