[Aavso-photometry] Adequate FOV size?

[Tandy, David]

I assume the problem that arises with imaging brighter stars is that one
should try to have comp stars brighter and fainter than the target star and
that is not always possible at the brighter magnitudes, right?

Also, why is binning detrimental if a sampling rate (maybe 3 pixels per
FWHM) is maintained?  I ask because I would still like to be able to shoot
through a short focus refractor occasionally for some pretty picture work
and small pixels are a better match at 800mm focal lengths while at 3556mm a
15-20 micron pixel works well.  Binning would provide that versatility but
at what expense in accuracy for photometry?

Dave

 

-----Original Message-----
From: aavso-photometry-bounces at mira.aavso.org
[mailto:aavso-photometry-bounces at mira.aavso.org] On Behalf Of Keith Graham
Sent: Thursday, December 30, 2004 2:52 PM
To: aavso Photometry
Subject: Re: [Aavso-photometry] Adequate FOV size?

> Necessary field size is largely dependent on the brightness of the 
> target object and the distance from the galactic plane.  I rarely if 
> ever have trouble at 11.5x11.5arcmin with the 1.0m telescope for the 
> "sweet-spot" objects around 14th magnitude, but quite often have 
> trouble getting good comp stars when trying to observe some 9th 
> magnitude object.

Agreed. I was thinking of only the fainter objects. If there are no brighter
comps nearby when the star goes into outburst, this could be a problem. But
even so, I find most of the charts I use have comps nearby that will cover
the outburst mags.

Keith









>    Larger fields often have other problems, such as vignetting, poor 
> flatfielding, curved focal plane (so not all objects are in focus), 
> and optical distortions.  Probably 20x20 is a convenient compromise.
> Arne
>
> Keith Graham wrote:
> > I see that a large FOV (30'x30') appears to be favored by some. I 
> > must
say that I have a 11.5'x11.5' fov with my ST9e and LX200 12". It is a very
rare occasion when I cannot get the variable and 3 comps from an e chart
within my fov. For photometry, I will use only f charts when available, and
these are well within my 11.5' x 11/5' fov. I will resort to the e charts
when no f chart is available, but even then there are plenty of comps from
which to choose that lie in my fov.
> >
> > Cheers,
> >
> > Keith Graham
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> >
> >
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