Telescope Reviews: Nikon 10X50 Cf Action Vi Binoculars

Tom ,

I'm not quite sure whether your latest question ( 7 x 50s)is in any way linked to my last post on this thread when I was suggesting the 10 x 50 versions of the same Pentax model for consideration by George , who specifically expressed an interest in 10 x 50s available in the UK.

Or I wonder are you simply asking the broader question about exit pupils of 5mm versus 7mm per se ?

Assuming the latter , it's a little ironic that over the past two days and nights I've exchanged several messages on another popular bino forum that I frequent , "defending" the 7mm exit pupil that I've spent the best part of two years contesting as a "waste of objective glass"

So at risk of sounding hypocritical in the eyes of anyone sad enough to recall any of my previous comments on the topic , my very latest thoughts are that generations of binocular designers who have forgotten more about optics than I will ever know can surely not all be wrong or stupid to have designed so many 7 x 50 , 8 x 56 , 9 x 63 , 10 x 70 and 11 x 80 binoculars over so many years.

I'm more than familiar with stories of sailors on rough seas in fading light needing that 7mm exit pupil but surely there can't have been THAT many sailors spending so much time scanning the horizons.

If there were so many, it seems odd that none of them ever seem to have left us any momentos of their experiences or joined forums such as these to add their few cents' worth , and in any case most of these 7mm exit -pupil binos are promoted as "astro -binos".

More recently , "accepted theory" seems to indicate that generally speaking people over around 50 years of age have maximum pupil dilation of only around 5mm in darkness.

I bravely pronounce that this assumption is somewhat flawed if not complete poppycock.

A noted regular contributor to this wonderful site ,let alone forum , who is over the age of 50 , has recently had his dilated pupils measured at 7mm --and that not in COMPLETELY dark -adapted circumstances .

There may well be very good arguments that a binocular with an exit pupil as large as 7mm is performing nowhere near it's maximum potential , but that is not to say that the same binocular will not provide a much more "bright , easy and comfortable " image than would the same body with higher power eyepieces.

Because terms such as "brightness " "ease of view" and "comfort" have no measurable units , they are unlikely to stand -up well in any technical tug of war against the advantages of higher power ( and thus smaller exit pupils) that CAN be measured in the very significant and universally accepted and very real properties of contrast and resolution.

So it is the old argument of "swings and roundabouts" , another example of the fact that no matter how good any particular binocular is for any specific intended purpose , there is always a compromise.

When you gain in power you lose in brightness and field of view , when you gain wider fields of view you tend to lose "flatness" -- a desired quality for stargazing.

Another "con" of a large exit pupil is that it amplifies any human eye astigmatism , making it virtually impossible for anyone with such afflictions and NOT wearing glasses or lenses to correct it, to attain "crisp ,sharp, clear " images , which again are terms not to be found in an optics expert's vocabulary but which are more "artistic" terms I have chosen to use intended to convey just about EVERYTHING desireable about a magnified image .

I happen to prefer very wide fields of view with hand -holdable low power and "easy to see with " 6mm exit pupils
which is why I wouldn't swap my Zeiss 7 x 42 for any binocular in that size or price range.

All this said , I would estimate that 90% of the time a 5mm exit pupil is ENOUGH IF NOT TOO MUCH for binocular astronomy pleasure and performance.

I hope this helps rather than confuses you Tom , or any other reader of this midnight waffle !

Regards -Kenny.

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Two eyes and a preference to use both

Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera