[Aavso-photometry] Obtaining Trans. Coeff's, Extinction Coeff's and ZP During Full Moon

[arne]

Steven Orlando wrote:
> Hello All!
> 
> Can one do an imaging run of a Landolt field through all their photometric filters for the purpose of determining transformation coeff's, extinction coeff's and ZP with the moon up, and get accurate coeffs. The field(s) are constant.
> 
> Bruce Gary mentioned to me purchasing a blue-blocker to block moonlight. I don't have one (yet).
> 
A blue-blocker is an interesting idea for unfiltered observations, as
it removes the blue end of the CCD response, reducing the effect of
scattered moonlight.  However, if used in conjunction with any
photometric filter, it hinders rather than helps.  Each photometric
filter already limits the wavelength response of the CCD; for the
Johnson-Cousins filters, only about 1000A is passed.  Therefore, a
blue-blocker will either have no effect, or else will just further
reduce the transmission through a filter without affecting the
contrast.

As for determining coefficients during full moon, you've already
gotten responses.  What I find is that the moon tends to get in
the way, as it is close to the equator this time of year when it
is full, and that is where most of the Landolt standards reside.
However, I've done coefficient calculations on any clear night,
moon or not, and if you can use moonlit nights for getting
coefficients and reserve dark nights for your science observations,
then you are clearly being more efficient.
Arne