[vsnet-chat 3361] Re: V382 Vel comparison stars

[aah@nofs.navy.mil]

Some comments regarding Stan's posting:
>I found that vignetting with the filters and the need to refocus
>(unfiltered and BVRI don't share the same focal plane) was a constant
>annoyance, as was the need to locate a series of new fields.
  You can purchase a clear glass filter of equal thickness to your
BVRI filters to make unfiltered observations parfocal with filtered
observations.  Why should the filters cause vignetting?  Perhaps
they are undersized for your system?  Locating new fields is certainly
a problem, though ameliorated by proper finding charts and GOTO capability.

>It's a waste of time making sequences if they're not adopted by everyone.
Now, this is a comment I agree with!  At least the AAVSO has now decided
to use Johnson V as a standard, which should make the use of Johnson-Cousins
photometric sequences more prevalent.

>You can either do sequences or CV monitoring, but in practice not both.
Here I beg to differ.  I reserve good photometric nights for projects
where standardization is needed, and then use the poorer nights for
differential photometry.  In a poor climate, you may only have 10percent
or so of available nights that are photometric, so the 'hit' is not
all that large.

>It seems the problem in this area is between magnitudes 10 and 11 which is
>a difficult area for CCDs in that you're back to ordinary sequential
>photometry over a wide field. I don't really want to get involved in that.
This is true if you don't have a wide field of view with the CCD.  It is
also the reason why I rarely do photometry brighter than 12th magnitude
with my 11x11arcmin field of view -- just too few good nearby comparison
stars.  You adjust your projects to optimize the use of your equipment.

Arne

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