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General Astronomy >> General Observing and Astronomy

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Mark Peterman
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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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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
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Reged: 05/11/06

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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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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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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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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
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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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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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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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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
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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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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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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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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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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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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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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
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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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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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dpwoos
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Re: Pupil Size new [Re: Tony Flanders]
      #5640890 - 01/24/13 03:05 PM

Let's be clear - my contention is that one's pupils contract and dilate in response to the brightness of what is seen through the eyepiece, and that other chemical stuff is going on is not in dispute. I also am claiming that when folks target a certain exit pupil for observing the Moon, or Jupiter, or M42, or M13, etc. they really have no idea what will be the actual diameter of their eye's pupil as it responds to the brightness of that exit pupil. So, it seems to me that I need to determine 1) the brightness levels of the exit pupils of various targets (e.g. by using a sky meter), and 2) the response of my pupil to those brightness levels in terms of pupil diameter.

The hard part will be controlling for pupil contraction/dilation from other sources: Pavlovian conditioning, fear, sexual attraction, etc. I will have to stay cool, calm and collected. Not my strong suit.


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Jon Isaacs
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Re: Pupil Size new [Re: dpwoos]
      #5640910 - 01/24/13 03:22 PM Attachment (12 downloads)

Quote:

. they really have no idea what will be the actual diameter of their eye's pupil as it responds to the brightness of that exit pupil. So, it seems to me that I need to determine 1) the brightness levels of the exit pupils of various targets (e.g. by using a sky meter), and 2) the response of my pupil to those brightness levels in terms of pupil diameter.




Dennis:

First, lets eliminate Jupiter and the moon, these are bright targets and normally observed at exit pupils smaller than the diameter of the eye during the day.

Then I suggest just measuring the diameter of your dilated pupil under a variety of low light conditions. I think you will find that the dilated diameter of you pupil does not change. There is so little light from the night sky that the pupil is always at it's maximum dilate if the skies are at all dark.

I just followed Tom's suggestion and photographed my dilated eye in a closet. I waited about a minute for the immediate dark adaptation finish. The flash wouldn't work without the LCD display turned on so it was not all that dark. Under those circumstance, my pupil was very close 7mm.

Jon


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dpwoos
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Re: Pupil Size new [Re: Jon Isaacs]
      #5641005 - 01/24/13 04:29 PM

Quote:

There is so little light from the night sky that the pupil is always at it's maximum dilate if the skies are at all dark.




I do not accept that because a sky is "dark" means that all exit pupils will be (even nearly) as dark, and I know you don't either as you specifically want to treat the Moon and Jupiter as exceptions though they reside in a dark sky. However, we don't have to settle this here and now. I am going to measure the brightness of some exit pupils and post the results. Then, if the data so warrants, we can subject ourselves to further cruel but necessary experiments (I see you have already begun) to determine our pupil's responses to these levels of brightness.

One other thing I have learned is that the pupils work together - a light producing a constriction of the pupil of one eye will produce a consensual constriction of the pupil of the other eye. This further complicates my testing, as I have to be careful that my bad eye doesn't taint the results by looking at something that it oughtn't.


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GeneT
Ely Kid
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Re: Pupil Size new [Re: csa/montana]
      #5641021 - 01/24/13 04:39 PM

Great advice!

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derangedhermit
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Re: Pupil Size new [Re: Jon Isaacs]
      #5641034 - 01/24/13 04:44 PM

http://www.ncbi.nlm.nih.gov/pubmed/15030828

http://www.ncbi.nlm.nih.gov/pubmed/22179219


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derangedhermit
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Re: Pupil Size new [Re: derangedhermit]
      #5641052 - 01/24/13 04:54 PM

As far as the apparent advantage of filling the pupil with light: aberrations increase dramatically (and variably on a per-eyeball basis) with larger pupil. In a number of people large enough that it makes it worth mentioning, a further increase in exit pupil results in a loss of resolution by the eye, due to the additional light at larger off-axis angles hurting the image more than it helps.

During daytime, the pupil ranges from around 3.75mm for young adults (on average, add disclaimers, ...) down to around 2.25mm for 60 year olds, where it apparently levels off as one ages further (on average, dah dah dah). Even this is large enough that some eyes' resolution benefits from a reduced pupil.


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Tony Flanders
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Re: Pupil Size new [Re: dpwoos]
      #5641079 - 01/24/13 05:13 PM

Quote:

Let's be clear - my contention is that one's pupils contract and dilate in response to the brightness of what is seen through the eyepiece.




Quite so. But do you have any evidence for that contention?

It's mighty hard to test, because one's pupils react to changes so quickly.


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Jon Isaacs
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Re: Pupil Size new [Re: dpwoos]
      #5641095 - 01/24/13 05:22 PM

Quote:


I do not accept that because a sky is "dark" means that all exit pupils will be (even nearly) as dark, and I know you don't either as you specifically want to treat the Moon and Jupiter as exceptions though they reside in a dark sky.




There is some confusion here.

The reason I want to treat Jupiter and the Moon differently is that one's pupil dilation does not matter, exit pupils that are reasonable for observing these objects will always be smaller than the dilated pupil, it doesn't matter if you pupil is dilated to 4 mm or 6mm or 3mm, the exit pupil of the eyepiece will be smaller than this.

- One has to distinguish between looking through the eyepiece at an object and the object being present in the sky. Jupiter being in the night sky will not affect the dilated diameter of your eye. It probably won't even affect it when you look directly at it in the eyepiece.

When it comes to Deep Space Objects, there is not enough light to cause a change in the dilation of the eye. As Tony and others have said, the eye dilates to it's maximum diameter quickly and it doesn't need to be very dark for it to happen. Go in a dark closest for a couple of minutes and watch your eye dilate.

Jon Isaacs


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Tom Polakis
Carpal Tunnel
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Re: Pupil Size new [Re: Tony Flanders]
      #5641108 - 01/24/13 05:28 PM

Quote:

Quote:

Let's be clear - my contention is that one's pupils contract and dilate in response to the brightness of what is seen through the eyepiece.




Quite so. But do you have any evidence for that contention?

It's mighty hard to test, because one's pupils react to changes so quickly.





I don't think it's all that difficult to test. Simply use an extreme range of brightness levels, and take flash photos. I am going to go out into my extra-bright backyard observatory, where the zenith sky brightness is around 18 mag/arcsec^2. Heck, I'll even let the light of Jupiter flood my vision. While I'm staring at the bright sky, I'll take the photo. Then I'll photograph my eyes in my pitch-black background, and see if the pupil diameter is larger. If my pupil size is equally large looking at my backyard sky, then it's safe to say that it doesn't vary while looking at much dimmer objects through an eyepiece.

Having mentioned my backyard observatory, we are currently entering a period of four or five days of likely overcast in Arizona, which is following one of the clearest months of Winter I have ever experienced. So maybe I won't be out there looking up at the rain tonight after all.

Tom


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dpwoos
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Re: Pupil Size new [Re: Tony Flanders]
      #5641128 - 01/24/13 05:41 PM

No, I don't have any evidence. Seems obviously true to me and I thought that most other folks would find it so as well, but I guess not! Now that I know that the pupils constrict in tandem, I am thinking it is possible to monitor the pupil size of the non-dominant eye while observing with the dominant one. That would be a pretty cool gadget - webcam, IR illumination, headband - maybe get one of my sons to test it for me? Just kidding, of course. After many years they still talk about how I made them and their friends ride around with me in our car in the dark with paper bags over their heads to do star counting. I think they are actually sorry that the state police didn't spot us. Anyways, simpler is to record the brightness of the exit pupil when observing a collection of targets (e.g. with a sky quality meter), and then to separately measure my pupil diameter when my eyes are exposed to the same light level.

What do you think?


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TexasRed
scholastic sledgehammer


Reged: 05/17/11

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Re: Pupil Size new [Re: Tom Polakis]
      #5641149 - 01/24/13 05:51 PM

Thanks to the original poster for starting this interesting thread. I had the exact same experience at my optometrist's a few weeks ago, except she said my dark adapted pupils measured about 6.5 mm at the age of 62, which beat the average of about 5.7 mm for my age. I had the same questions about the accuracy and validity of that.

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Tom Polakis
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Re: Pupil Size new [Re: TexasRed]
      #5641753 - 01/24/13 11:52 PM Attachment (20 downloads)

This is one of the weirder things I have posted on a forum.

Here are my and my wife's pupils fully dilated after five minutes in a black, indoor room. In addition to the scale, the white lines superimposed on all four pupils are 7mm long. Mine are just slightly shy of 7mm, and my wife's just more than 6mm.

Tom


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BlueGrass
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Re: Pupil Size new [Re: Tom Polakis]
      #5642027 - 01/25/13 07:21 AM

I've rethought my post and I'm going to try this. I'm on the downside of 55 and this could be something I can use at my next optometrist visit ...

Edited by BlueGrass (01/25/13 12:13 PM)


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Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Pupil Size new [Re: BlueGrass]
      #5642217 - 01/25/13 09:46 AM

Page 52 of RASC's 2013 Observer's Handbook has a great exit-pupils diagram. According to the diagram, the average exit pupils by age are as follows:

Age 10: 7.7mm
Age 20: 7.3mm
Age 30: 6.9mm
Age 40: 6.5mm
Age 50: 6.1mm
Age 60: 5.7mm
Age 70: 5.3mm
Age 80: 4.9mm

Best,
David


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Mark Peterman
super member


Reged: 08/07/12

Loc: Texas
Re: Pupil Size new [Re: BlueGrass]
      #5642223 - 01/25/13 09:49 AM

Thanks to everyone who responded to my original question. I guess I was a bit suprised to learn that I am at least a 6mm. For some reason I had figured it would be less.

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derangedhermit
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Re: Pupil Size new [Re: Widespread]
      #5642821 - 01/25/13 03:36 PM

Quote:

Page 52 of RASC's 2013 Observer's Handbook has a great exit-pupils diagram. According to the diagram, the average exit pupils by age are as follows:

Age 10: 7.7mm
Age 20: 7.3mm
Age 30: 6.9mm
Age 40: 6.5mm
Age 50: 6.1mm
Age 60: 5.7mm
Age 70: 5.3mm
Age 80: 4.9mm

Best,
David



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.


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derangedhermit
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Re: Pupil Size new [Re: Tom Polakis]
      #5642840 - 01/25/13 03:44 PM

Quote:

This is one of the weirder things I have posted on a forum.

Here are my and my wife's pupils fully dilated after five minutes in a black, indoor room. In addition to the scale, the white lines superimposed on all four pupils are 7mm long. Mine are just slightly shy of 7mm, and my wife's just more than 6mm.

Tom



Pupils contract at near focus as part of the accommodation process. You need to be focusing on a distant object, say on the other side of the room (15-20 ft away).

Please tell your wife for us that she has pretty eyes


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dpwoos
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Re: Pupil Size new [Re: derangedhermit]
      #5642889 - 01/25/13 04:09 PM

So when I look through an eyepiece is it near or far focus?

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Mr. Bill
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Re: Pupil Size new [Re: dpwoos]
      #5642907 - 01/25/13 04:19 PM

Quote:

So when I look through an eyepiece is it near or far focus?




The ep creates a virtual image that is (as far as the eyes concerned) at infinity.


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Tom Polakis
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Re: Pupil Size new [Re: derangedhermit]
      #5642936 - 01/25/13 04:32 PM

Quote:

Quote:

This is one of the weirder things I have posted on a forum.

Here are my and my wife's pupils fully dilated after five minutes in a black, indoor room. In addition to the scale, the white lines superimposed on all four pupils are 7mm long. Mine are just slightly shy of 7mm, and my wife's just more than 6mm.

Tom



Pupils contract at near focus as part of the accommodation process. You need to be focusing on a distant object, say on the other side of the room (15-20 ft away).





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


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

Thanks! Ordered one.

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derangedhermit
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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
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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
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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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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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Re: Pupil Size new [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
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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
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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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