Re: [Utah-astronomy] Measuring pupil size

Easiest way is to use a set of metric allen wrenches. While looking at a bright star in the dark, slowly wave an allen wrench back and forth. If the allen wrench is smaller than you eye's pupil you will see difraction effects from the light passing both sides of the wrench at the same time. Your pupil size will be between the largest wrench where you see the effect and the next largest size where you don't see it. This method is at least 20 years old, I have no idea where I first read about it. But you need to hold the wrench so the light passes the flat sides and not the edges so the width is the true size of the wrench. DT