Science Buddies: "Ask an Expert"

Hi Sciencebuddies!

I am attempting to complete the project described on the page https://www.sciencebuddies.org/science- ... #procedure. But today, while I tried to go through the calibration process, I ran into a problem that I'm not sure how to fix. My camera would not take pictures if the white paper filled the whole view. It would literally refuse to take a picture. Can anyone please let me know if there is a way to complete this project without having the white paper fill the entire field and if there is a way, how would that potentially affect my results for the calibration curve and EET values? Moreover, can someone please describe to me what the relevance and purpose is of using white paper for the calibration instead of per say, a differently colored picture?
Please let me know as soon as you can!
Thanks in advance for all the help!

Hello Tigerlover1,

Most digital cameras automatically focus the lens before taking a picture. The automatic focus needs some contrast (or an edge) in the field of view. I think your camera may not be able to automatically focus on the paper. Some digital cameras prevent taking a picture if the lens is not focused properly. This may be the reason that your camera won't take pictures of the white paper.

You can try setting the camera to the manual focus mode. And there may be an option to turn off the feature that prevents taking a picture if the lens is not focused.

If these suggestions don't work, you can try taking the calibration pictures without having the view filled with the paper. Then you'd need to crop the images (with an editing program) so that nothing showed except the paper.

The calibration provides the range of exposure times your camera needs to produce pixel values from zero to the maximum. White paper is a good choice because it is readily available and should produce a maximum pixel value without an excessive exposure time.

I hope this helps. Please ask again if you have more questions.

A. Norman