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#26 derangedhermit

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Posted 24 January 2013 - 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.

#27 Tony Flanders

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Posted 24 January 2013 - 05:13 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.


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.

#28 Jon Isaacs

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Posted 24 January 2013 - 05:22 PM

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

#29 Tom Polakis

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Posted 24 January 2013 - 05:28 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.


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

#30 dpwoos

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Posted 24 January 2013 - 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?

#31 TexasRed

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Posted 24 January 2013 - 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.

#32 Tom Polakis

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Posted 24 January 2013 - 11:52 PM

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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#33 BlueGrass

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Posted 25 January 2013 - 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 ...

#34 Widespread

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Posted 25 January 2013 - 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

#35 Mark Peterman

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Posted 25 January 2013 - 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.

#36 derangedhermit

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Posted 25 January 2013 - 03:36 PM

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.

#37 derangedhermit

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Posted 25 January 2013 - 03:44 PM

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 :)

#38 dpwoos

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Posted 25 January 2013 - 04:09 PM

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

#39 Mr. Bill

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Posted 25 January 2013 - 04:19 PM

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.

#40 Tom Polakis

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Posted 25 January 2013 - 04:32 PM

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

#41 GeneT

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Posted 25 January 2013 - 06:55 PM

Thanks! Ordered one.

#42 derangedhermit

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Posted 25 January 2013 - 07:36 PM

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.

#43 Tony Flanders

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Posted 26 January 2013 - 07:18 AM

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.

#44 derangedhermit

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Posted 28 January 2013 - 07:12 PM


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.

#45 orion61

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Posted 28 January 2013 - 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.

#46 Tony Flanders

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Posted 29 January 2013 - 06:25 AM

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.

#47 Mr. Bill

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Posted 29 January 2013 - 03:20 PM


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


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

#48 derangedhermit

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Posted 29 January 2013 - 08:56 PM

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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