Re: V image fainter than I

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

I don't see what you gain.
If you leave the exposure as it currently is, you have lots of
unmatched Ic stars.
If you stop down the Ic camera, then you have the same number of
matched V/Ic pairs, but you've lost the unmatched stars.
If you increase the exposure, you pick up the current unmatched
stars with matches to the longer V exposure, but now you lose
the 2/3 stars that would normally appear on the full-aperture Ic
frame.
   So the only gain with stopping down the Ic camera is to remove
the unmatched Ic stars.  Software removes them already, but gives
you the option of sometime in the future using these unmatched
objects in some other way.  Why not just leave things alone?
Arne

droege@snapmail.us wrote:
> Richard,
> 
> This does not work.  A star that is saturated in I is not saturated in V
> and so is lost.  There are lots of I stars for which there is no V star
> detected, like a factor of 3.
> 
> The scheme would be to stop down the I camera and take longer exposures so
> that at the faint level there was a rough match of detection.
> 
> Tom Droege
> 
> 
>>Speaking as a lurker, I'd change the V vs I parameters in the data
>>reduction
>>process to accept the difference.  Don't throw out (or block) good data.
>>
>>Richard
>>
>>-----Original Message-----
>>From: owner-tass@listserv.wwa.com [mailto:owner-tass@listserv.wwa.com]On
>>Behalf Of droege@snapmail.us
>>Sent: Friday, 18 March, 2005 13:20
>>To: tass
>>Subject: V image fainter than I
>>
>>
>>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?
>>
>>
>>
>>
> 
> 
> 
> 
>