Re: V image fainter than I

[Arne Henden <aah@nofs.navy.mil>]

This is no different than the case of going through a reddened region,
where you see more Ic stars than V stars.  Just leave everything alone
and have a few more unmatched Ic measures.
   In general, the throughput between V and Ic is about equal for most
CCD cameras.  Stars tend to be brighter at V and the QE is higher at V
(not Ic, as Tom suggests), so the net effect is to compensate for the
wider Ic bandpass.  My usual exposure times are about 1.2x longer
at V than Ic.
Arne

droege@snapmail.us wrote:
> As I am setting up the camera for the coming run I notice the V camera is
> even fainter than usual from the I camera. I don't know why and have
> changed out the camera.  We shall see if it is a camera problem when I get
> some clear sky.  I have done all the obvious things like look through the
> lens for dead bugs and hanging chad.
> 
> There has always been a bad match.  Many stars are lost because they are
> too bright in the I images and others are too faint in the V.
> 
> Rob tells me that different exposure lengths are a pain.  The alternative
> is to stop down the I camera.
> 
> The I filter has about twice the bandwidth of the V filter, further the
> CCD is more sensitive in I.
> 
> At the moment, the I camera has a great focus.  I really hate to throw
> away all those photons now that they pass through the optics so well.
> 
> Should I stop down the I lens?
> 
> Any comments?
> 
> 
>