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Dialated pupil measurement - how?

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#26 laedco58

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Posted 12 April 2020 - 10:02 PM

I had the optometrist measure mine when I was in recently for an eye exam. In a semi dark room she measured them to be 7mm.


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#27 tommm

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Posted 13 April 2020 - 11:38 AM

 

 

...You can experiment if you observe near some woods.  Walk into the woods in the middle of the night and continue to stare at the ground for at least 5-10 minutes.  Then turn around and look at the clearing you just walked out of.  Bright, isn't it?  Now, look down.  You can no longer see what you were just looking at and the only light that damaged this night vision was the light in the clearing from the sky!

The sky itself is much brighter than that, and can really knock down your night vision capabilities.  Imagine how much damage to your night vision the use of a bright red flashlight or tablet does.

And, through all of that, your pupil probably stayed the same...

 

I few years ago I did a 20+ mile hike mostly off-trail and it took me longer than planned because I had to wade through chest high tobacco brush and wind through manzanita for about a mile, and detour around a steep-sided gorge. It was in a wilderness area far from terrestrial lights.  I was about 2 miles from my car when it became completely dark on a moonless night.  I had decided a half hour before to take a more well-used, wider, trail for the last couple miles so I could see it, though it took me out to the road about a mile from my car. The way I had planned went through thicker pine forest and I figured there was no way I would find my way through there.  I don't think there are any conditions to get your eyes more dark adapted, but all I could see was the trail was just a tad lighter than the surroundings. There was hardly any difference between it and the sagebrush I knew was alongside it, but could not see at all.  I also couldn't see rocks, so steps off of granite steps in the trail were a surprise. I walked very slowly trying to see but all I could see was a very slightly lighter area where the trail was, no other structure at all, so I mostly felt my way with my feet. I walked off the trail at a bend, and after several steps thought it seemed a bit darker, so wasn't the trail, and walked back to where the "ground" was a bit lighter.  I knew the road was just down the hill at one point and was very tempted to shortcut, but I also knew there was thick sagebrush there even though I couldn't see it at all.  As I walked along the road to my car I couldn't see the road surface either, and it felt awkard walking with no visual reference to where the ground was - except when the occasional car would pass. I was amazed at how dark it was.  The stars overhead seemed really bright. I avoided looking at them though because as you say I couldn't see as well afterward. I usually carry a headlamp, but forgot it that day.
 



#28 kjkrum

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Posted 17 April 2020 - 12:34 AM

What we need is a mobile opthalmologist to give eye exams at star parties using those eye drops that are so awful during the day...

#29 Starman1

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Posted 17 April 2020 - 01:06 AM

What we need is a mobile opthalmologist to give eye exams at star parties using those eye drops that are so awful during the day...

And awful at night too because they open your pupils so wide astigmatism results and the drug prevents your eye from focusing well.
Not useful for astronomy, I'm afraid
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#30 Jon Isaacs

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Posted 18 April 2020 - 06:36 AM

And awful at night too because they open your pupils so wide astigmatism results and the drug prevents your eye from focusing well.
Not useful for astronomy, I'm afraid

:waytogo:

 

Dark adaptation is about the chemical processes in the eye. Large exit pupils are rarely optimal so even if one's were artificially dilated and there were no other side effects, it's just not very important.  Probably the biggest advantage to a large dilated pupil is that it might make eye placement easier, it's a bigger target.

 

Jon




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