Age and light grasp

[jaymoynihan]

I was recently rereading parts of "Choosing, Using & Repairing Binoculars" by J. W. Seyfried. In it he went over the whole thing about the 7-8mm maximum exit pupil of the human eye. And also, as one ages, the max exit pupil decreases, until, on the average, it is down to 4mm by your mid-50's.

Assuming this is correct, and assuming all other things being equal, would this mean regarding the differences between say, a 10x42 and a 10x50 binocular, for a person in their mid-50's:

In dim light, or at night*:

1. the 50mm would still provide a slightly higher resolution (not factoring in hand tremor etc.)

2. The 50mm would not provide increased light grasp.

:brains:

* if i remember correctly during regular sunlit daylight, the max exit pupil is 2-2.5mm, no matter what ya using.

[Fireform]

My own experience suggests that that oft-cited guideline is to be taken with a grain of salt. I'm 48 and I have no trouble at all seeing the difference between bins with exit pupils of 4 and 5 in dim conditions.

Larger exit pupils are also less critical of eye placement and thus often quicker to get on the view with.

[Kevin Purcell]

The variance in those averages is quite large (plus or minus 1mm I've seen quoted).

So that can only be taken as a trend not an absolute (as Fireform points out).

As I've mentioned many times you can measure you own pupil size in many light conditions with a digital camera and a ruler held to your forehead for scale. Turn red eye off. Adapt to the lighting condition then take the photo. Try it in the dark and the bright sun to find your full range (and also in "dim" conditions like overcast).

[jjg213]

Hi, I used Kevins system of a plastic rule held near the eye and waited for about 20 minutes in the dark before taking a picture. I was in dis-belief when the pupil measured just over 6.5mm. A few weeks later I had a routine eye test and asked the optometrist to measure my pupil, confirmed again at about 6.7mm. So now my 7x42's, 7x50's and 8x50's are still fully useable.
I will be 70 this year!
John

[Kevin Purcell]

Hi, I used Kevins system of a plastic rule held near the eye and waited for about 20 minutes in the dark before taking a picture. I was in dis-belief when the pupil measured just over 6.5mm. A few weeks later I had a routine eye test and asked the optometrist to measure my pupil, confirmed again at about 6.7mm. So now my 7x42's, 7x50's and 8x50's are still fully useable.
I will be 70 this year!
John

As you demonstrate the rules of thumb aren't that accurate for quite a few folks.

[BobinKy]

Read about the optical discussion I had with my eye doctor at this thread: http://www.cloudynights.com/ubbthreads/showflat.php?Cat=&Board=binoculars&Number=2764337&Forum=,f33,&Words=&Searchpage=1&Limit=25&Main=2764337&Search=true&where=bodysub&Name=26058&daterange=1&newerval=&newertype=&olderval=8&oldertype=m&bodyprev=#Post2764337

...Bob
Kentucky

[Alexis Powell]

As you demonstrate the rules of thumb aren't that accurate for quite a few folks.

The recommendation to not bother with large exit pupil binos if you are in the upper age bracket should never have become a rule of thumb. Maybe we need to start a campaign to do away with it. It is one of those oh-so-clever bits of "expert advice" that is really disinformation. The two or three papers on aging and maximum pupil dilation that I've read (maybe if I have a free moment I'll look one or two up again and add a link) all found a decrease in population average maximum pupil dilation with age, but that individual variation in maximum dilation at a given age was so large that the population trend is _absolutely uninformative_ w/respect to making individual decisions/recommendations. There is simply no alternative to measuring one's own pupils. For myself, I don't feel like the issue is of any practical significance in bino choice for most birding. I don't generally choose to use a particular bino because of the impact of exit pupil on low light performance. Rather, I use the largest bino (though never over 35 oz) that I can comfortably carry/pack on a given venture. The easier view provided by large exit pupil binos (because of easier eye alignment) is a much more important consideration for birders, and eye pupil diameter matters little for that.

--AP

[BobinKy]

The recommendation to not bother with large exit pupil binos if you are in the upper age bracket should never have become a rule of thumb. Maybe we need to start a campaign to do away with it. It is one of those oh-so-clever bits of "expert advice" that is really disinformation. The two or three papers on aging and maximum pupil dilation that I've read (maybe if I have a free moment I'll look one or two up again and add a link) all found a decrease in population average maximum pupil dilation with age, but that individual variation in maximum dilation at a given age was so large that the population trend is _absolutely uninformative_ w/respect to making individual decisions/recommendations. There is simply no alternative to measuring one's own pupils. For myself, I don't feel like the issue is of any practical significance in bino choice for most birding. I don't generally choose to use a particular bino because of the impact of exit pupil on low light performance. Rather, I use the largest bino (though never over 35 oz) that I can comfortably carry/pack on a given venture. The easier view provided by large exit pupil binos (because of easier eye alignment) is a much more important consideration for birders, and eye pupil diameter matters little for that.

--AP

Alexis...

You make some very interesting points. For daytime observing I think two issues you mentioned are important: Low light and eye alignment.

My own pupils measure 5mm in a lighted doctor's office, but probably less in full sunlight. Here in Kentucky we have heavy foilage in most of our forests during the summer, which limit available lighting. I have noticed a significant difference between the 4mm and 5mm exit pupil when observing under full foliage. When observing under full sun I cannot tell the difference.

Your point of eye alignment is an important issue for binocular selection, environment, and targets observed. I agree completely that objects on the fly require the easy eye alignment that large exit pupils afford. Viewing on the water or from a moving vehicle also require large exit pupils. On the other hand, viewing landscapes from a stationary position do not require easy eye alignment and smaller exit pupils easily deliver.

...Bob
Kentucky