Re: correcting slope

[droege@wwa.com]

Last night I did the experiment of varying the VCO and looking at the
PSF.  I just took Norman's "vertically" as a measure.  The proceedure
was to shift to a new VCO point and wait for the CCD to clear out the
old value.  Then "vertically" was watched for typical values.  The 
minimum value for 5 PSF presentations was then picked.  A much lower
value for the V filter was thrown out at 10650 as probably not 
representative.  Obviously this is not a great way to do this 
measurement, but the data does not look too bad.  

I found the best point for the V filter to be a 0.907 second period.
The best value for R and I was found to be 0.922.  So there is quite
a difference, and the compromise value of 0.915 shows noticable trailing
in V (but not R and I).

Here is the data:

VCO           E (I)     M (R)     W (V)        Period
10800        2.47       2.42      2.03       .895    
10700        2.33       2.28      1.69       .903
10650        2.26       2.33     <1.66       .907
10600        2.10       2.03      1.60       .913
10550        1.88       1.69      1.96       .915
10500        1.84       1.42      2.23       .922
10450        2.06       1.94      2.30       .926
10400        2.26       2.17      2.46       .930     

Seems like there are two things we might do:

A) Hold a mad filter exchange so that some run VVV cameras and some III.

B) Do nothing and find a compromise VCO setting.

I slightly lean to B.  I would rather have both filters from one location
than the best PSF.  But it depends on how the software handles this.  What
say Mike G. and Arne???

Tom Droege

On Tue, 26 Aug 1997, Glenn Gombert <gleng@infinet.com> wrote:
>
>        Differentail-trailing is the best explination that I have seem for
>the gradient that occurs in TASS images and is probably what is occuring. As
>Tom posted eariler the best that can be done is to chose a VCO rate that
>gives the best "average" results between the three cameras.....
>
>
>Glenn G. 
>
>
>>>Mike G.
>>It is entirely possable that the images are smearing.
>>You are tracking for some rate in the middle of the field. 
>>The northern part goes slower than the middle.
>>The southern part goes faster if you are looking at a northern Dec........!
>>Bob
>>
>>
>Glenn Gombert <gleng@infinet.com>
>
>
>
>