Sky Quality Measurement

[chiltonstar]

As an alternative to buying an SQ meter, can I use my DSLR to get an assessment of SQ, eg by taking a 10 sec exposure, ISO 800, 18mm lens, and then use the histogram to get a relative measure of sky brightness??

Anyone done it?

If practicable, how could you then convert the relative measurement to an absolute scale?

I'm asking because I want some actual data to pressurise my local council re lighting for a large housing development very close to an AONB (N Wessex Downs).

Chris

[dph1nm]

Should be possible. You would need to image an unsaturated star of known magnitude (on a clear night) then count how many ADU were in it (having subtracted the background). This will then let you calculate the magnitude of 1 ADU on that image. You then count how many ADU you get from sky (less dark) inside an area of 1 square arcsecond (use a larger area and scale down). You can then get the sky brightness in magnitudes/sq.arcsec. Ideally you would do this for each colour channel separately.

NigelM

[LeoLion]

If by sky quality you mean 'sky glow' then this http://media.skyandtelescope.com/documents/SkyglowDigitalCameras.pdf might do the job you require . I have a pal over in Leeds whose been looking at sky brightness changes using the method as a new lighting scheme is rolled out.