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After experimenting a bit I can see the parallax reduction effect that the article talks about using a magpul AR-15 rear sight I had lying around. It's more noticeable if you compare the amount of parallax with and without the aperture, all else being equal. It's very impressive but it still doesn't seem to work for with with the actual rifle pointing at a reasonably distant target.
I think there are a few reasons:
* I noticed that the effect is far more pronounced with a shorter sight radius, and unsurprisingly, with a closer target.
* I suspect that the numbers they picked for the example in the paper are a little exaggerated. They use a 1mm aperture and a 4.2mm camera to simulate the human pupil. But 1mm is close to the smallest aperture you ever see on target sights. AR-15s have 1.8mm apertures, Tech Sights come with a 1.5mm as standard. And 4.2 seems to be towards the bigger extreme for a human pupil in good light .
I happen to have one of those cardboard scales used for measuring interpupilary distance (it came with my glasses). I held it up to my eyes and took a selfie, then zoomed in and measured out 4mm on the photo of the scale with my caliper. The width of the caliper jaws was then easily twice the diameter of the pupil in the photo. Now the scale was a few mm in front of my pupil so it's far from a perfect measurement, but I am confident that 4.2mm is an unrealistic estimate for moderate indoor light, and probably a worse one for good outdoor light. It seems to me that with a typical 1.8mm aperture and good light, the aperture and pupil could be very close to being the same size at least for my eyes.
Of course I already knew from experience that sight alignment matters for me with this rifle, but it's good to be able to reconcile my experience with the theory in the paper. I'm interested to see how things work out with smaller apertures as zukiphile suggested.
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