# Thread: Good Idea? or not?

1. ## Good Idea? or not?

Last allergy season, I noticed that after using visene allergy, the eye that I put the drops in, started to "overexpose" (to use a photography term) well, just about everything. I went to a mirror to check things out, and noticed that my pupils were no longer the same size! The allergic eye was now several times bigger than the non-allergic eye.
So I guess, what I am getting at, is that to aid your night vision, a few drops in your eyes should open up those pupils....

A good thing? Or a bad thing?

Justin

2. Dilating your pupils will let more light in.

It also allows the funkier parts of your lens to admit light, emphasizing the flaws in your vision. You will experience more astigmatism and other vision defects than with smaller pupils. (This is why they recommend using bright lighting when reading.)

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deaman49 (06-28-2011)

4. It would only make a difference if the diameter of the exit pupil of your telescope is larger than your normally dark adapted eye pupil diameter.

Normal healthy humans, who aren't on drugs or medication, have a dark adapted pupil diameter of around 7mm. This is closer to 6mm if you're old, and 8mm if you're young. So, for most people, if the exit pupil diameter of your scope is less than 6mm it will not be improved by dilating your eye's pupil, as the limiting factor is your scope not your eye.

To calculate the exit pupil size of your telescope you simply divide the diameter of your scope in mm by the magnification.

Don't know the magnification? Divide the focal length of the scope by the focal length of the eyepiece.

For example, if the focal length of your scope is 1200mm and you're using a 25mm eyepiece, that gives a magnification of 1200 / 25 = 48x. If the diameter of the scope is 8" (200mm) then the exit pupil size is 200 / 48 = 4.1mm. Thus, in this example, so long as your eye's pupil is 4.1mm or greater in diameter, you will not be letting any more light into your eye by dilating it.

With the example scope above, you'd have to get into the realms of 40mm EPs and as low as 30x magnification before the exit pupil starts to get too big for normal dark adapted eyes to fully utilise

Of course it depends on the scope setup. The shorter the focal length, wider the primary lens/mirror, and bigger the EP, the bigger the exit pupil size.
Last edited by VincentMcKenzie; 06-27-2011 at 10:35 PM.

5. ## The Following 4 Users Say Thank You to VincentMcKenzie For This Useful Post:

andyst4545 (06-28-2011),Apollo17 (06-29-2011),deaman49 (06-28-2011),DrNature (06-27-2011)

6. Hey! I learned something again.
Clear Skies!
Lee

7. I guess this question would have made more sense if I worded it more specifically toward general stargazing.

I understand the concept of only as much as the smallest diameter orifice( I work in autobody, so the airhose for sprayguns is my "real world application"

Thanks for the input guys!

Justin

8. If you are REALLY OLD like me then maybe 5mm is all you will get when your eye is dark adapted.