I will be 68 before the end of the year and my pupils dilate to 6.8mm in a DARK (SQM-L 22.8) room. No chemicals. MEASURED in dim red light after allowing time for adaption. Charts be hanged. Some folks older than me dilate even more.
And I say get the ES82 30mm. It's more useful in more circumstances. I have an ES68 40mm and a 31T5 Nagler. The 31T5 is more often useful, by far. The 40's a nice ep but the ES82 30 is a better one with better edges than the ES68 40 and a flatter field than my big Nagler. I have owned it too. Max TFOV is wonderful but it's not as simple as the arithmetic. You're close enough w/the ES82 30 that you'll never notice and the field will be really nicely rendered.
I have other ep's that render exit pupils up to 9.3mm in some of my scopes. Now & then I give 'em some focuser time to see the effect of very large exit pupils and also to enjoy the crisp presentation despite the lower efficiency.
Precisely where did you get that dictum? My own experience is precisely the opposite.
Like you, I think that eye pupil size is somewhat of a red herring -- but in the opposite direction. Let me tell you my own experience.
My experiences agree with both Dick and Tony. My scopes are mostly around F/5, the 12.5 inch operates at F/4.67 with the Paracorr, the 16 and the 22 inch are at F/5.06 with a Paracorr, the NP-101 is at F/5.4. My longer focal length eyepieces include the 21mm Ethos, 31mm Nagler and the 35mm and 41mm Panoptics. I play around with large exit pupils. I am 70 and about 18 months ago I photographically measured my pupil at about 7.7mm.
About the only time I find a near maximum exit pupil to be useful is when using an H-Beta or maybe an O-III filter for large dim objects. Good examples are Barnard's Loop or the HorseHead with an H-Beta. Otherwise, I almost always see more with the 31mm and 21mm Ethos. A smaller exit pupil means a larger image scale so details are more easily seen. The contrast of an extended object is unchanged but the contrast of a star, open cluster or to a certain point, a globular cluster is dramatically improved by increasing the magnification. Doubling the magnification does not affect the brightness of the star but it dims the background sky by a factor of 4, that's 1.5 magnitudes greater contrast. Increasing the magnification can make cluster come alive as those faint tiny stars pop out.
Something to consider: Even under dark skies, the sky glow is bright enough to affect the dark adaptation of the eye. Dimming the sky glow and the object with a smaller exit pupil means that the eye can be better dark adapted, this would be the photo-chemical aspects which are the important aspects of dark adaptation. I think this is why I really only notice an improvement of dim objects using an 8mm exit pupil if I use an H-Beta filter or possibly an O-III filter. The sky is so much darker with a narrow band filter, my eye can more fully dark adapt. An H-Beta or O-lll filter might have a bandwidth of 12nm, the brighter part of the visual spectrum is around 200nm, this means the sky is dimmed by about 3 magnitudes, a sky that is 21 mpsas is now about 3 magnitudes dimmer at 24mpsas, a factor of about 17.
And too, as much as I enjoy wide field viewing with the big, bright exit pupils, and as much as I am a vocal proponent of large exit pupils and wide fields of view, the vast majority of the objects out there are small, making them larger is probably the most important aspect of seeing them better.
As a finder eyepiece, I primarily use the 21mm Ethos, at F/5, the 4mm exit pupil is plenty bright but the increased magnification means that I can see small objects like galaxies etc much better than with the 31mm Nagler. The 13mm Ethos provides a 2.6mm exit pupil and it is even better for picking out small objects, the field of view gets somewhat narrow, less than 1/2 degree in the 22 inch but I can certainly pick out the faint fuzzies.
As far as measurements:
Two-hundred sixty-three individuals participated.
For participants aged 18 to 19 years (n=6), the mean dark-adapted pupil diameter was 6.85 mm (range: 5.6 to 7.5 mm);
20 to 29 years (n=66), 7.33 mm (range: 5.7 to 8.8 mm);
30 to 39 years (n=50), 6.64 mm (range: 5.3 to 8.7 mm);
40 to 49 years (n=51), 6.15 mm (range: 4.5 to 8.2 mm);
50 to 59 years (n=50), 5.77 mm (range: 4.4 to 7.2 mm);
60 to 69 years (n=30), 5.58 mm (range: 3.5 to 7.5 mm);
70 to 79 years (n=6), 5.17 mm (range: 4.6 to 6.0 mm);
80 years (n=4), 4.85 mm (range: 4.1 to 5.3 mm).
These values were consistent with studies using infrared photography. The standard deviation was >0.1 mm in 10 (3.8%) participants, all of whom were younger than 55 years."
However, in my experience, the main takeaway is that very large exit pupils, very large dilated pupils are rarely an advantage and one almost always sees more with a 6 mm exit pupil rather than with an 8mm exit pupil as well as with a 4mm exit pupil rather than a 6mm exit pupil. There are specific circumstance when I will choose large exit pupils, the Heart and Soul nebular complex is large and dim, low contrast, a 7+mm exit pupil with a narrow band filter is about optimal.
Bottom line: Get the 31mm Nagler/30mm ES 82 degree. Get the 41mm Panoptic/40mm ES 68 degree after you purchase the 21mm Ethos/ 20mm ES 100 degree if you want to see what it looks like. I think you will find most folks working at F/5 rarely use a 40mm eyepiece. Even for those with large dilated pupils, it's just rarely an advantage.