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# Thread: How Small A Gap Can you See?

1. ## How Small A Gap Can you See?

As I get older, my vision has degraded. But how bad has it become? Using a pair of parallels and a bit of shim stock, I could test my ability to see tiny gaps.

If you are interested, please see

https://rick.sparber.org/SeeingGap.pdf

Your comments are welcome. All of us are smarter than any one of us.

Thanks,

Rick

2. ## The Following 3 Users Say Thank You to rgsparber For This Useful Post:

mwmkravchenko (05-11-2019), Scotsman Hosie (05-11-2019), Seedtick (05-10-2019)

3. I'm not sure about establishing tenths accuracy using parallels that probably aren't flat to that accuracy. It might be interesting to repeat the experiment using two optical flats.

It's generally agreed that the angular resolution of a healthy human eye is about one arcminute or 0.3 milliradians. Thus the smallest separation that could be detected would depend on viewing distance (why we like to hold things closer to the eye when inspecting detail).

However, I think it would be naive to apply that to your experiment directly since, as an example, distinguishing separation between two lines on a grating just isn't the same thing as detecting when the light "winks out" in your experiment. I'm sure the backlighting in your experiment is very important but I'm not sure how to reconcile it with the one arcminute resolution.

I know I'm not being very helpful but I appreciate your attempt to quantize something we all do. Keep up the good work.

4. ## The Following 2 Users Say Thank You to mklotz For This Useful Post:

mwmkravchenko (05-11-2019), Scotsman Hosie (05-11-2019)

5. If your "finger pressure" is enough to "bend" the parallels, then I dont think they qualify as parallels

6. I suggest you try it. I can bend the head of my mill down by a thou with a hand on top. Bending a parallel by 0.0001” doesn’t take much force.

Rick

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