Exit Pupil

[Alien 13]

When I was a lad it was always said that 7x50 was the way to go and I can even remember 10x50s being frowned upon by Sky at Night presenters in the 70s my own experience with large exit pupils was a WW2 tank scope ithe 70mm objective and 6x magnification and nothing I have looked through since has come close so whats changed in the last 40-50 years is it LP that has made smaller EP more popular.

Alan

[ollypenrice]

I take the naive view that anything above about 5mm may not get into my 62.7 year old pupils. However, this may be a naive view. Following with interest.

Olly

[ChrisLX200]

If you're 18 yrs old or less your pupil will likely expand to around 7mm, the older you get the more restricted it gets due to aging muscles and old folk like Olly ( ;-) ) and me it's likely 5mm or less even when fully dark adapted. To add insult to injury, your cornea yellows with age making things appear even more dim. I recall my mother having an eye operation for a cataract where they replace the lens and she remarked how 'blue' and 'bright' things looked afterward. Anyway, 7x50 would be good for youger folk while we seniors :-) would be better off with 10 x 50.

ChrisH

[pipnina]

If you're 18 yrs old or less your pupil will likely expand to around 7mm, the older you get the more restricted it gets due to aging muscles and old folk like Olly ( ;-) ) and me it's likely 5mm or less even when fully dark adapted. To add insult to injury, your cornea yellows with age making things appear even more dim. I recall my mother having an eye operation for a cataract where they replace the lens and she remarked how 'blue' and 'bright' things looked afterward. Anyway, 7x50 would be good for youger folk while we seniors :-) would be better off with 10 x 50.

ChrisH

I'd heard people who get cateracts can become sensetive to near-ultraviolet wavelengths. That would be pretty cool if that happened, though I wouldn't rush to get new eye lenses since there is a risk of... "Retinal detachment" which does NOT sound appealing!

In regards to exit pupils... I think lower ones do tend to respond better to LP to a certain extent but, really, the best way to find out what exit pupil is best is by trying multiple on each target you view. 7mm may wash out the target, 5 down to 3 may provide a segnificant improvement in contrast and 2 and below may dim the object... But it will depend on your sky conditions and the object being viewed... So try everything

My scope only came supplied with EPs for up to 3.5mm exit pupil... I had considered getting a 32mm EP to bring that up to 4.6... But I decided it wasn't worth it and I should save for a better scope instead.

[ChrisLX200]

I remember as a kid looking at Coma Berenices (naked eye) and thinking it was a beautiful cascade of sparkling diamonds. These days I doubt I could see it at all. Skies were better back then - and I lived in the sticks so no LP.

ChrisH

[acey]

When I was a lad it was always said that 7x50 was the way to go and I can even remember 10x50s being frowned upon by Sky at Night presenters in the 70s my own experience with large exit pupils was a WW2 tank scope ithe 70mm objective and 6x magnification and nothing I have looked through since has come close so whats changed in the last 40-50 years is it LP that has made smaller EP more popular.

Alan

Bear in mind, those instruments weren't specifically intended for astronomy. They were expected to be used in daytime when the eye pupil is typically 3mm. But also, 19th century observatory telscopes were often used with over-size exit pupils. The concern about "wasted light" does seem to be a relatively recent thing.

[ronin]

Agree with Acey the instruments mentioned are/were designed for daylight use - looking at the greater spotted lesser striped loony bird on a branch 80 yards away with the sun shining off it.

The criteria for the real sort of astronomy binocular are the comet hunting types with 45 degree angled and interchangeable eyepieces.

[BinocularSky]

My £0.02:

• 7x50s were favoured by the Navy as low-light binoculars because 7x magnification was about the max usable on the heaving deck of a boat. Birders tend to limit themselves to 8x (usually 40 or 42) for a similar reason (but they use hand-held binoculars in a different way - typically considerably longer on a given target -  to astronomers.
• I consistently see more in the night sky with 10x50s than with 7x50s (my pensioner-pupils still do 6.3mm) and, even under very dark skies, there are very few objects that I find easier with 7x50s (M33, NGC7000, M101 lurch to mind). I'm beginning to like 8x42s more, but still not as much as 10x50s.
• The only generalisation about age and dark-dilated pupil is that for each individual, it will tend to decrease as s/he ages. The variation within any given age cohort is enormous. See this table:

• Glass quality makes an enormous difference. I've mentioned this before, but we tested this earlier this year: we could see M79 low on the horizon with a hand-held Leica 10x40s, but not with a mounted Celestron Skymaster 15x70.

[Alien 13]

Thanks everyone for your views I get the feeling that there might have been a lot more quality 7x50s around in the early 60s due to there populariy with the military so it was probably natural to point them skywards, I do miss the the lack of low power optics even if some of the EP is wasted.

Another factor that might be involved was the inky black skys I had when I was a kid.

Alan

[Stub Mandrel]

Woo-hoo! In a darkened room right now my pupils are about 6mm, and the other night they were a good 7mm when I was dark adapted - certainly equal to my daughters' and she's only 16 (we were comparing them).

This seems to be pretty awesome for 54 in a few weeks! So there's something good about my poor short-sighted, astigmatic and over-presured peepers!

Now I've always been pretty good at seeing my away round in the dark, I wonder if this is why.