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General Astronomy >> General Observing and Astronomy

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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Pupil Size new [Re: csa/montana]
      #5643162 - 01/25/13 06:55 PM

Thanks! Ordered one.

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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Pupil Size new [Re: Tom Polakis]
      #5643218 - 01/25/13 07:36 PM

Quote:

The room was completely black, so there really was nothing to focus on. What do eyes do in this situation? I know that they have a problem coming to focus on a blank sky (looking for Venus in the daytime, for example). Do you know if they also contract in complete darkness?

Tom



My guess is that if there is nothing to focus on, then the pupils are relaxed, and wide open. The effort to focus on near objects invokes the decrease in size. But as I say, that is only a guess.

You don't need absolute darkness to do this, since the night sky isn't absolute darkness. An indoor test at night with the closet door cracked into a dark room with just enough light to see something on the other side, will eliminate any doubt.


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Tony Flanders
Postmaster
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Pupil Size new [Re: derangedhermit]
      #5643879 - 01/26/13 07:18 AM

Quote:


It is common for a person to have several tenths of a millimeter difference from the average age. I guess that's why people measure their own.




Forget tenths! It's very common for people to have a full millimeter difference from their age average, and not rare to have two millimeters difference.

I doubt that it's possible to measure your pupils accurate to a tenth of a millimeter. Nor is there any reason to do so.


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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Pupil Size new [Re: Tony Flanders]
      #5648995 - 01/28/13 07:12 PM

Quote:

Quote:


It is common for a person to have several tenths of a millimeter difference from the average age. I guess that's why people measure their own.




Forget tenths! It's very common for people to have a full millimeter difference from their age average, and not rare to have two millimeters difference.

I doubt that it's possible to measure your pupils accurate to a tenth of a millimeter. Nor is there any reason to do so.



The studies I read showed a variation of 0.8mm among participants of similar age. I wasn't willing to go beyond that. There's not much difference between "several tenths" and "a full mm". Perhaps worth an ! to some...

Your pupils can certainly be measured to a tenth of a mm, for example using an infrared instrument designed to measure pupil diameter.

I didn't suggest a need to measure a pupil to a tenth of an mm.


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Pupil Size new [Re: derangedhermit]
      #5649139 - 01/28/13 08:08 PM

On My DSLR Nikon I can disable the auto focus and set it up on a tripod. This could be done by anyone with similar equipment.
After getting everything lined up, you could use a remote shutter release, After sitting in the Darkened room for 15 minutes or so, fire the remote. The flash will be fast enough the pupils won't have the chance to constrict.
It would be a bit painful.
I am lucky at 51 I still reach 7mm down only .5 mm from my 20's. I was in the optical business for about 15 yrs, Until I couldn't take the whining Optometrists any longer. LOL
I rarely need the full 7mm because I prefer to kick the power up a bit anyway. I like the larger image scale, even if it is at the cost of a bit of brightness.
Then again at F-10 It seems my 6" sct is as bright as my 8" just a smaller image scale. I can see as much detail on DSO
objects on the smaller scope as long as the object is fairly large. It isn't until I look at Planets that the difference is apparent.


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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Pupil Size [Re: derangedhermit]
      #5649743 - 01/29/13 06:25 AM

Quote:

My guess is that if there is nothing to focus on, then the pupils are relaxed, and wide open. The effort to focus on near objects invokes the decrease in size. But as I say, that is only a guess.




Sounds plausible, but boy is this hypothesis going to be hard to test! You can attain total darkness by doing flash photography in a windowless room, but you can't focus in total darkness.

The whole discussion reminds me a little of Schrodinger's cat.


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Mr. Bill
Postmaster
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Reged: 02/09/05

Loc: Northeastern Cal
Re: Pupil Size new [Re: Tony Flanders]
      #5650561 - 01/29/13 03:20 PM

Quote:



The whole discussion reminds me a little of Schrodinger's cat.




I think we've pretty much reached the end of this thread...RIP


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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Pupil Size new [Re: Tony Flanders]
      #5651154 - 01/29/13 08:56 PM

Quote:

Quote:

My guess is that if there is nothing to focus on, then the pupils are relaxed, and wide open. The effort to focus on near objects invokes the decrease in size. But as I say, that is only a guess.




Sounds plausible, but boy is this hypothesis going to be hard to test! You can attain total darkness by doing flash photography in a windowless room, but you can't focus in total darkness.



Trivial. Starting in total darkness, measure pupil diameter while trying to see something close and then something far away at intervals while gradually increasing the light level until the difference in diameter due to accommodation is noted. Compare this set of measurements v. first measurements.

As far as "can't focus in darkness", I'm not sure that's entirely correct. I can at least unfocus (blur) by trying to when looking at a nearby object. I can't tell where focus then is, but there is some degree of conscious control of focus. It may be that by one knowing beforehand how far away something is, and looking at or for it in darkness, the eye adjusts, even when it can't see it. I think it is possible.


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