Science Buddies: "Ask an Expert"

Hello!

I am conducting a variation of the Science Buddies project, "Using a Digital Camera to Measure Skyglow". In this variation, I will attempt to use the spectral information (red, green, blue values) of the skyglow images to determine the main source of the skyglow. I was just wondering about the calibration part of this experiment. When you use the white paper for calibration, are you trying to expose the camera's sensor to the brightest amount of light possible? And if that is so, I believe that all measurements would have to be relative to the white paper (the brightest). And if that too, is correct, then how would you expose the sensor to the darkest amount of light possible, since the measurements would have to be relative? If I am not making sense, please tell me. Thank you very much for your consideration in this issue.

Sincerely,
LookingToTheSkies

Hi LookingToTheSkies,

I think I'm answering your question, but if I'm not, please let me know!

The goal of the calibration is not to exposure the sensor to the brightest light possible. The goal is to see how the pixel values in an image change as the amount of light entering the camera sensor changes. You change the amount of light entering the camera's sensor by varying the exposure. The most light will enter the sensor during the longest exposure; the least light will enter the sensor during the shortest exposure. Take another look at the background section of the project idea, which explains this in more detail, and then post back with any remaining questions you have.

You are correct that the measurements made using this procedure are all relative. That's why the procedure refers to an "equivalent exposure time" instead of an absolute measurement of brightness. You would need a different - and much more complicated - procedure to measure absolute brightness.

Thank you very much! I think you've cleared it up for me. Have a great day!