Re: Sky Quality Meter

Hi Dan,

That is a fast lens! As you say, the count rate is similar to the open
(with CM500 filter) detector we are using. As you know this is just the
Lagrange invariant at work!

We have tested the spot to zenith-pointing-SQM offset and find that it
is about 0.65 mag/sq arcsec
using visual bandpass CCD photometry with standard stars of known Vj
and (B-V)j (i.e. a minus-IR filter) which is most similar to the
bandpass of our detector/filter combo. Both light pollution and natural
OH- airglow are strongly concentrated to the red end of the spectrum,
so we believe that our test is a more fair/accurate comparison than
using Vj.

We are certainly interested in improving the calibration with
additional input and cross-checks. As mentioned in another post, these
will almost certainly be zeropoint corrections which can be applied for
specific purposes.

Best regards,
Doug

.

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