Measuring skyglow with a camera

[Emmyd_24]

Hi, I'm doing the measuring skyglow with a digital camera experiment and I've analysed the calibration photos with the imagej software and have written it all down. I'm having trouble making the graph, I understand that I have to graph the mean of the histogram but what I'm having trouble with is what numbers I have to put on the x axis- the exposure times. I don't know how to convert the exposure times (30 sec, 15 sec ect) into a logarithmic scale, I'm not that great at maths Also I don't know what graph paper to use. Thanks

[theborg]

Emmyd_24,
Welcome and thank you for your question. You don't need to convert any of your values if you use the right graph paper. You will need to get a special graph paper called "semi-log" paper. You can make it yourself, but it's much easier to buy it. This is a graph that is a normal linear scale on one axis and a log scale on the other. You want the kind that is linear on the vertical (Y) axis and log on the horizontal (X) axis.

An alternative is to use a graphing program like Microsoft Excel. To do this, plot your data using a scatter plot then right click on the x-axis and select "format axis", then under "axis options" tick the "logarithmic scale". Leave the base as 10.

In both cases, paper or excel based, exposure time should be plotted on the x-axis (log scale) and pixel average on the y-axis (linear scale).

[Emmyd_24]

Thankyou very much, your reply was very helpful

[theborg]

That's great. If you have any more trouble or inquiries, please don't hesitate to ask.