Subject: Re: WRT Daniel Comments

From: Tony Tyson

Submitted: Thu, 24 Apr 2003 14:10:16 -0400

Message number: 121 (previous: 120, next: 122 up: Index)

OTCCDs present yield and uncontrolled PSF ellipticity problems.
But that array design is attractive.  CMOS could solve the dynamic
range problem as well as the mechanical shutter problem.  Cost is
high now, but will be driven down.  We plan to compete CCDs and
CMOS hybrid arrays for a while before deciding. A list of specs is
on lsst.org/Project.

I agree that we must get adequate astrometry (0.1" for WL science)
and good photometry (2%).

We discussed filters before and concluded that we need two in the
g region, possibly BV.  I think this was driven by two science cases.
One of them was the need to get color-z for WL.

Tony

Dave Monet wrote:
> 
> Daniel makes good points, but I am not ready to give up yet.
> 
>   1) During the recent astrometric and photometric calibration meeting,
>      the importance of tying LSST into external standard systems was
>      noted many times.  My point for a ND filter is that LSST occupies
>      such a unique position in telescope/detector space that the
>      Project (and not the community) needs to develop a road map for
>      making sure that LSST is "on the system".  We did the 600
>      pound gorilla thing with SDSS, and unless there are really good
>      reasons for defining yet another photometric and astrometric
>      system for LSST, transformations to existing systems are just
>      as important as getting clear skies.
> 
>      My point was not so much as requiring an ND filter, but rather
>      that the Proposal needs to address tying LSST into external
>      astrometric and photometric systems.  We need to think about
>      this, and to add pieces to the design if such are necessary.
>      We can always remove these if other projects obviate them.
> 
>   2) CMOS is great for the dynamic range problem, but OTCCD would be
>      much more useful if we needed to start guiding before the
>      structure stopped shaking.  Maybe we will identify a sensor
>      technology that tastes great and is less filling before
>      we actually start cutting metal.
> 
> -Dave
> 
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