Measuring Your Eye's Entry Pupil With a Digital Camera
Version 1.0 of 12/3/2004-1:00 a.m.
Measuring your eye's entry pupil for astronomy is easy if you have a
digital camera. In this example, the author used the Nikon Coolpix 2200.
- Go out in the dark and let your eyes adapt for 1-2 hours.
- Have someone take a picture (with a flash) of your main eye (or aim
the camera to your eye and take the picture yourself). Be sure to look
at the lens. Here's what the author's eye looks like:
- After you transfer the picture to your computer, open it with Photoshop.
- Invert the pupil and change the contrast to force the boundary of the
iris to stand out.
- Keeping the Shift key down, draw a horizontal diameter for the iris. Here's what it looks like in my case:
- Change the "Units and Rulers" under "Preferences" to "cm" and "mm".
- Magnify the image using "ctrl-+" and measure the length of the
line against Photoshop's ruler.
- The author's reads 14 ticks, which divided by two gives ~7mm.
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