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Estimate the angular resolution of the human eye at the centre of the visible wavelength range during daylight. Using your answer, estimate the surface den- sity of rods (per mm2) on the retina, assuming that they critically sample the image.

The first part is easy you just use the angular resolution formula.It's the second part I'm having trouble with namely the critically sampling bit.

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    $\begingroup$ This sounds like a homework assignment, which we don’t usually answer on AstronomySE. $\endgroup$ Dec 30, 2023 at 16:18
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    $\begingroup$ It’s also a really bad homework question, because you have no rods in the very center of your vision, which is the only place you actually have high resolution. $\endgroup$
    – Topcode
    Dec 30, 2023 at 17:44
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    $\begingroup$ @PierrePaquette from Community Policy Repository in meta, find Are homework questions allowed? See also Stop the off-hand "this sounds like a homework question" comments that offer no guidance and raise false flags? I think we can offer some help improving the question. $\endgroup$
    – uhoh
    Dec 30, 2023 at 23:19
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    $\begingroup$ Hi @Rob, this question, and your other question Hi,Just wondering if anybody could help me with this exam question on radio telescopes, shown below? show no evidence of effort. The first comment someone should have left is "What did you try?" For this type of "homework-like" question where you state a detailed problem to work and just ask for the answer rather than insight, it's necessary to explain exactly where the problem is - how far you got and where you are getting stuck. Until then, down votes for lack of research will continue. $\endgroup$
    – uhoh
    Dec 30, 2023 at 23:23
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    $\begingroup$ I’m voting to close this question because this is rather a biology or physiology question. I fail to see the relation to astronomy. That said, please follow uhoh's advice on how to ask meaningful questions: dive into them yourself, see how far you get, with whatever assumptions you can make and their justifications, share your results and thought process and ask for clarification and guidance for exactly the point you seem to get stuck. $\endgroup$ Dec 31, 2023 at 10:55

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Here's how I would do it.

Estimate the angular resolution of the human eye at the centre of the visible wavelength range during daylight.

you mentioned in your comment

The first part is easy you just use the angular resolution formula.

Likely you mean the Rayleigh criteria discussed in Wikipedia's Airy disk.

$$\theta = 1.22 \frac{\lambda}{d}$$

where $d$ is the daytime pupil diameter and $\lambda$ is the

centre of the visible wavelength

Make sure to keep your units straight, convert both of them to the same units (nm or um or mm or m) before division.

The question asks about sample density in mm^-2 ("per mm2") at the back of the eyeball. so draw a triangle from the center of the pupil to the retina, and use the small angle approximation $\tan \theta \approx \sin \theta \approx \theta$ and multiply your $\theta$ by the diameter of the eyeball to get the resolution in mm at the retina.

Then google "critical sampling" and find Wikipedia's

to calculate your sampling frequency (neurons per mm).

Then square that to get neurons per mm^2.

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