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General Astronomy >> General Observing and Astronomy

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Mark Peterman
super member


Reged: 08/07/12

Loc: Texas
Pupil Size
      #5640279 - 01/24/13 09:45 AM

I recently had my annual eye exam and while there I asked to have my dark adapted pupil measured. The doctor said he doesn't get that request very often.

Anyway, he turned off the lights except for one dim light behind me. I would say that it was at least as bright in the room as a full moonlit night.

He waited 60-70 seconds and begin measuring. He came up with a measurement of "about 6mm". Does this sound reasonable for a 48 year old?

Since the room was 1) not fully dark and 2) white light was on and 3) he only waited a minute, is it safe to assume that my dialated pupil could be more than 6mm?

Mark


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csa/montana
Den Mama
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Reged: 05/14/05

Loc: montana
Re: Pupil Size new [Re: Mark Peterman]
      #5640352 - 01/24/13 10:25 AM

I would say that one minute is not enough time for your pupil to become completely adjusted; however, doctors spending the necessary time (20 min. or so), ties up the exam room & puts other patients in the waiting room much longer.

You might try this pupil gauge at home, before you start observing.

Pupil Gauge


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Darenwh
Carpal Tunnel


Reged: 05/11/06

Loc: Covington, GA
Re: Pupil Size new [Re: csa/montana]
      #5640365 - 01/24/13 10:34 AM

Actually, though your eye may dilate a small amount more as you wait longer, it likely wouldn't be much more. At most, half a milimeter, probably less. Dark adaption is more than just a larger pupil size. Much of dark adaption is due to chemical changes in the vitrious fluid of the eye. This is what takes 20+ minutes to be completed.

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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Pupil Size new [Re: csa/montana]
      #5640369 - 01/24/13 10:35 AM

Quote:

I would say that one minute is not enough time for your pupil to become completely adjusted.




As far as I can tell, all the pupil adjustment happens within seconds. However, I can't say for sure because I've never been able to measure my pupils with better accuracy than 0.5 mm.

Dark adaptation continues to improve for a half hour or more, but that's mainly due to chemical changes in the retina.

Anyway, 6 mm seems dead normal for a middle-aged person.


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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: Pupil Size new [Re: Tony Flanders]
      #5640440 - 01/24/13 11:03 AM

6mm tells me you'll love most all widefields......

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Mr. Bill
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Reged: 02/09/05

Loc: Northeastern Cal
Re: Pupil Size new [Re: Tony Flanders]
      #5640473 - 01/24/13 11:26 AM

Quote:



As far as I can tell, all the pupil adjustment happens within seconds. However, I can't say for sure because I've never been able to measure my pupils with better accuracy than 0.5 mm.

Dark adaptation continues to improve for a half hour or more, but that's mainly due to chemical changes in the retina.

Anyway, 6 mm seems dead normal for a middle-aged person.




At 65, my pupil dilation is about 5mm....and it doesn't get better as you age, as lots of other body stuff.



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dpwoos
Pooh-Bah
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Reged: 10/18/06

Loc: United States
Re: Pupil Size new [Re: csrlice12]
      #5640478 - 01/24/13 11:31 AM

Folks talk about this all of the time, but I never hear anyone question (except me) how accurate any such measurement can be given that the brightness of what we see is very dependent on the target as seen through the eyepiece, and so at any given moment who knows the amount of dilation?! For this reason, I think the whole endeavor of measuring one's dark adapted pupil and then using that number in any kind of actual observing context is bogus.

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Mr. Bill
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Reged: 02/09/05

Loc: Northeastern Cal
Re: Pupil Size new [Re: dpwoos]
      #5640493 - 01/24/13 11:36 AM

You can measure your pupil dilation at the telescope by using successively lower mag eps....you look for when the "fieldstop" is actually the edges of your pupil which is never completely round.

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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Pupil Size new [Re: dpwoos]
      #5640520 - 01/24/13 11:54 AM

Quote:

Folks talk about this all of the time, but I never hear anyone question (except me) how accurate any such measurement can be given that the brightness of what we see is very dependent on the target as seen through the eyepiece, and so at any given moment who knows the amount of dilation?! For this reason, I think the whole endeavor of measuring one's dark adapted pupil and then using that number in any kind of actual observing context is bogus.




I believe that the eye quickly dilates to essentially its maximum aperture and then the chemical processes that are the major part of dark adaptation begins.

The surface brightness of any extended object is proportional to the square of either the exit pupil or the eyes entrance pupil, whichever is smaller. If you eye is dilated to 6 mm and exit pupil is 6mm then it would 4 times as bright/intense as that same object viewed with a 3mm exit pupil.

Jon Isaacs


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dpwoos
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Reged: 10/18/06

Loc: United States
Re: Pupil Size new [Re: Jon Isaacs]
      #5640532 - 01/24/13 12:01 PM

I think you are missing my point? Some targets are brighter than others, and so one's pupil will adjust depending on the target. There is no one number that is valid for all targets. In fact, I think this fact accounts for why it takes time at the eyepiece to see a lot of detail in anything - one's "dark adaption" needs time to adapt to whatever is coming out of the eyepiece for that target.

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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Pupil Size new [Re: Tony Flanders]
      #5640563 - 01/24/13 12:23 PM

Quote:

Quote:

I would say that one minute is not enough time for your pupil to become completely adjusted.




As far as I can tell, all the pupil adjustment happens within seconds. However, I can't say for sure because I've never been able to measure my pupils with better accuracy than 0.5 mm.

Dark adaptation continues to improve for a half hour or more, but that's mainly due to chemical changes in the retina.

Anyway, 6 mm seems dead normal for a middle-aged person.






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Tony Flanders
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Reged: 05/18/06

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Re: Pupil Size new [Re: dpwoos]
      #5640643 - 01/24/13 01:07 PM

Quote:

Folks talk about this all of the time, but I never hear anyone question (except me) how accurate any such measurement can be given that the brightness of what we see is very dependent on the target as seen through the eyepiece, and so at any given moment who knows the amount of dilation?! For this reason, I think the whole endeavor of measuring one's dark adapted pupil and then using that number in any kind of actual observing context is bogus.




I strongly suspect that the Moon and Sun are the only astronomical targets bright enough to make your pupils contract.

Contrary to widespread lore, my measurements indicate that there's no difference in pupil size between full and moderate darkness, such as one would find on a typical suburban ball field at night. At least for me ... can't speak for other people.


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Tom Polakis
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Reged: 12/20/04

Loc: Tempe, Arizona
Re: Pupil Size new [Re: dpwoos]
      #5640656 - 01/24/13 01:11 PM

Quote:

I think you are missing my point? Some targets are brighter than others, and so one's pupil will adjust depending on the target. There is no one number that is valid for all targets. In fact, I think this fact accounts for why it takes time at the eyepiece to see a lot of detail in anything - one's "dark adaption" needs time to adapt to whatever is coming out of the eyepiece for that target.





Unless you are looking at objects with very high surface brightness with a very large scope, I think the pupil remains at its maximum size. I have noticed that dark adaptation can be affected briefly after viewing a bright object, but that's at the low level of the biochemical changes people have brought up in this thread.

A great way to measure pupil diameter (when you have no observing plans) is to wait a couple minutes in a completely darkened room, and then take a flash photo while you hold a ruler near your eyes. Then measure it from the photo. I got 7mm with a precision of better than 0.5mm last time I tried it. Note that an electronic flash this isn't the most pleasant thing to look at when you're dark adapted, but it won't kill you either.

Tom


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dpwoos
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Reged: 10/18/06

Loc: United States
Re: Pupil Size new [Re: Tony Flanders]
      #5640704 - 01/24/13 01:33 PM

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright - seems to me more so than walking out of the optometrists without the disposable sun glasses. Looking at an unfiltered moon results in total blindness. Even my Quickfinder and Telrad have to be dimmed almost to extinction, and only newbies use a red light at anything other than the lowest possible level. A green laser beam is like a stick in the eye. Also, and as I said, I think that one reason why it takes time at the eyepiece to see faint/difficult stuff is that it takes some time for the eye to adjust to the field brightness. So, my guess is that there is a HUGE amount of mythology about entrance pupil size and dark adaption. Maybe or maybe not so much on faint fuzzies, but certainly on many targets that I think most folks would agree appear really, really bright through the eyepiece.

Our club has a dark sky meter, and the next time I observe at our site I am going to use it to check the brightness through the eyepiece when positioned on different targets. Good idea?!

BTW, I just read on Wikipedia that pupil dilation/contraction is also affected by sexual attraction. I don't know about you old folks, but in my case that is still something that has to be factored in.

Edited by dpwoos (01/24/13 01:45 PM)


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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: Pupil Size new [Re: dpwoos]
      #5640730 - 01/24/13 01:45 PM

Quote:

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright - seems to me more so than walking out of the optometrists without the disposable sun glasses. Looking at an unfiltered moon results in total blindness. Even my Quickfinder and Telrad have to be dimmed almost to extinction, and only newbies use a red light at anything other than the lowest possible level. A green laser beam is like a stick in the eye. Also, and as I said, I think that one reason why it takes time at the eyepiece to see faint/difficult stuff is that it takes some time for the eye to adjust to the field brightness. So, my guess is that there is a HUGE amount of mythology about entrance pupil size and dark adaption. Maybe or maybe not so much on faint fuzzies, but certainly on many targets that I think most folks would agree appear really, really bright through the eyepiece.

Our club has a dark sky meter, and the next time I observe at our site I am going to use it to check the brightness through the eyepiece when positioned on different targets. Good idea?!




I discovered long ago, in any field or endeavour, given X number of people, you'll get X number of opinions....we're all different. For all our discussions, rants, and raves, bottom line is, only the eyeball to eyepiece will tell...


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Pupil Size new [Re: dpwoos]
      #5640777 - 01/24/13 02:03 PM

Quote:

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright - seems to me more so than walking out of the optometrists without the disposable sun glasses. Looking at an unfiltered moon results in total blindness




Your eyes entrance pupil is not relevant when viewing the planets and double stars because they are done at higher magnifications and small exit pupils. In any event, a dark adapted eye is not the best choice for viewing planets, adding some ambient light is one technique used by planetary observers to prevent dark adaptation.

The discussion here I believe is about observing deep sky objects were dark adaptation is critical. In this situation, the eye will be fully dilated regardless of the brightness of the DSO.

Bye the way, viewing the moon does not result in total blindness, it just results in losing ones dark adaptation. It's probably the only object bright enough and large enough to cause this loss. The contraction of the pupil when viewing the moon is the reason that one can often see the secondary's shadow at low magnifications.

Jon


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Tom Polakis
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Reged: 12/20/04

Loc: Tempe, Arizona
Re: Pupil Size new [Re: dpwoos]
      #5640778 - 01/24/13 02:03 PM

A better way of determining if Tony's observation about pupil size applies to you would be to go out in a suburban setting in which you can barely see the Milky Way, and take the flash photo of your eyes with a ruler, as I recommended. Then close yourself in a dark room, and do the same thing. The darkest sites in the world are nowhere near the darkness of an indoor room, so you will be overestimating the difference. Then report your measurements here.

Tom


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John Bordelon
journeyman


Reged: 08/31/11

Loc: Marietta, GA
Re: Pupil Size new [Re: Mark Peterman]
      #5640802 - 01/24/13 02:12 PM

I asked my ophthalmologist this question about a year ago. I am 71. The answer was that my open iris measured about 4mm. I should point out that my iris has been affected by the use of eye constriction drops for many years, a necessity because of my glaucoma. The 4mm value was about what I had measured previously.

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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Pupil Size new [Re: dpwoos]
      #5640839 - 01/24/13 02:34 PM

Quote:

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright.




Yes, the planets can appear painfully bright for a short time, at least through a big telescope. But that's due to the chemical changes, not the pupil size. It takes your pupil a measurable fraction of a minute to dilate fully, but it takes less than a second for them to contract.

Try it. Go into the bathroom at night, turn the light off, and wait for a minute. Stand in front of the mirror and flip the light on. You can actually see your pupils contract. It's even more obvious if you look at someone else's eyes.


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Jon Isaacs
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Re: Pupil Size new [Re: Tom Polakis]
      #5640847 - 01/24/13 02:38 PM

Quote:


A great way to measure pupil diameter (when you have no observing plans) is to wait a couple minutes in a completely darkened room, and then take a flash photo while you hold a ruler near your eyes. Then measure it from the photo. I got 7mm with a precision of better than 0.5mm last time I tried it. Note that an electronic flash this isn't the most pleasant thing to look at when you're dark adapted, but it won't kill you either.





Tom:

I have wondered about doing this. My concern is whether the image is in focus. How did you ensure that the camera was focused? Or maybe it just was???

Jon


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