Science Buddies: "Ask an Expert"

ok, so I understand part of the experiment but what I don't understand is does the calibration curve have to be as perfectly curved as the one in the example and should the numbers end up being the same? Also, Im really confused about how you actually find the EET by using the graph... from looking at the example it gives no clear indication. My last question, does the layout of the graph itself have to be the same as the one in the example in order to find the EET? ( Also I cannot use graphing paper so it has to be done digitally, which is becoming an issue)

OK... thats all the questions I have for now. Thanks!
Anna

Hi Anna,

Your calibration curve will have a different shape then the one shown in the example. The average pixel values for a particular exposure time will probably also be different. These differences arise because the image sensor in your camera is different from the image sensor in the camera used to make that example calibration curve. The calibration curve will be slightly different for every camera.

As far as the graph goes, it's important that you have exposure time on the x axis and average pixel value on the y axis. The x axis needs to be on a logarithmic scale; the y axis on a linear scale. (A linear scale is the default in most graphing programs, including Excel.) Your range of average pixel values may be different, and that's OK. The colors you choose for the various lines and data points are totally up to you.

To find the EET, check your data tables to see what the average pixel value was for one of your sites. Then find that value on the y axis. Draw a straight, horizontal line from that point on the y axis until you reach the calibration curve. Then draw a vertical line from the intersection down to the x axis. The x axis value that your line intersects is the EET.

I hope this helps. Please post back with other questions!