I bought a Canon EOS 1000D with EF-S 18-55 and I immediately thought of sperficiale try to measure the magnitude of the sky using the camera. The method I described it in this post and some below.
Before now I had a compact digital camera with a small CCD and limitations of sensitivity, which did not allow me to measure over 20.-20.5. The EOS 1000D with its large CMOS sensor is more sensitive and can easily reach 23 and go.
The photograph (click to enlarge) I took it back home with the manual setting: ISO1600, 30, F3, 5. I have cleared the elaborations that increase the contrast, sharpness, color saturation, and I set the temperature color day.
You see the Big Dipper. orgiginale Pictured are visible stars of about magnitude 8.
reading levels of intensity on the picture (with any utility) is in the somewhat 'brighter near the Big Dipper R = 128, G = B = 72 and 61 that correspond to surface magnitude 18.99 (in red) 19.97 (in green) and 20.23 (in blue). The SQM
at that moment I gave readings around 19:01 to 19:05 (I have a sky of 19, 5 + mv, behind the house, which would make the happiness of so many amateur astronomers sedentary, but not mine). The direct comparison can not be done strictly speaking, because the scale R, G, B and SQM photometric scales are different (different spectral sensitivity). The maximum sensitivity of the SQM is around 500-600 nm (see article Cinzano ) then somehow reading the SQM should be compared with R and G. If we take the average of R and G leaves 21:48, which would be compared with the SQM that says 21.03. There are about 4 tenths of a difference, on which I propose to investigate.
Whatever happens, the result is good and, above all, the photograph provides more information. For example tells us that the bulk of the IL is already in the red and green there is a magnitude more (and in fact with the deep sky filter visually improve the situation). We also notice slight irregularities of the bottom polluted. In a previous photo on the recognition of the glazes.
One thing I like to do is a time-lapse fork that points to the Casera Razzo Friuli, during the night to see how you change the IL. We'll see ...
For those wishing to use the same method, following this link you can download an Excel spreadsheet where you can set the parameters of the camera's exposure and the levels read on photography. The paper calculates the magnitude and the surface also shows in a chart.
The spreadsheet assumes that photography is encoded in the sRGB color space (some fotocasmere allow you to choose more than one color space: Choose this).
http://rapidshare.com/files/222586514/misure_digicam_v3.xls.html
Addendum.
I delete the background sky (by cutting up to those levels of light pollution) and is a nice photo with stars up to magnitude 7 (click to enlarge). Too bad it's a trick.
