[Comm2011] Fwd: Re: some data... to be better analyzed

[helmich]

-------- Original Message --------
Subject: Re: some data... to be better analyzed
Date: Fri, 01 Apr 2011 17:30:56 +0200
From: Lothar Noethe <lnoethe at eso.org>
To: Pietro Schipani <pietro.schipani at oacn.inaf.it>

Dear Pietro,

it would be nice if you could generate the PSF anisotropies also for the
images 2011-04-01T06:18:06.160 and 2011-04-01T06:20:30.072.
If the orientations of the elongations do not change, there are two
possibilities.
  1. The defocus range may be too small.
  2. The elongations are, at least partially, generated by coma.
The elongations should, as a function of defocus, first increase
linearly, then reach a maximum and then go down rather slowly.
To check if the range was large enough, one could try to get into the
range above the maximum.
I attached a note describing the expected elongations as functions of
the coefficients of defocus, astigmatism and the seeing.

Ciao
Lothar

On 01/04/2011 11:05, Pietro Schipani wrote:
> Dear Konrad and Lothar,
>
> 1) during this night we have produced some sets of through focus images,
> using an observation block (donuts) which takes first an image of the
> field and then two defocus images (moving M2 by -0.2 and +0.2mm). I have
> not had a look yet, we are producing more data than I can analyze
> quickly...
>
> The fits files are automatically copied through EVALSO to Garching, from
> which I could access asking Stefano Zampieri (the files are there for
> some days, then they are deleted for storage problems).
>
> For example a set of such 3 images (taken at rot angle=0) is in the
> folder /OMEGA/2011-03-31/raw
>
> OMEGA.2011-04-01T06:18:06.160.fits.fz
> OMEGA.2011-04-01T06:19:03.501.fits.fz
> OMEGA.2011-04-01T06:20:30.072.fits.fz
>
> The PSF anisotropy of the first one is shown in the attached image
> 061806.jpg.
>
> In the same folder there are also other sequences at rot=90-180-270,
> starting at
>
> rot=0: 06:18:06
> rot=90: 06:31:40
> rot=180: 06:42:27
> rot=-90: 06:54:31
>
> 2) We also took focus sequences (2 fits files each, image + focus
> sequence) at the same rot angles (physical angles) in order to measure
> the tilt.
>
> rot=0: 06:05:00
> rot=90: 06:25:30
> rot=180: 06:36:52
> rot=-90: 06:48:53
>
> but I still was not able to analyze the data with the Konrad's program,
> it has failed but maybe it's my fault.
>
> These tests have been done at an altitude angle of about 50 deg.
>
> 3) We measured defocus differences with the Shack-Hartmann with the
> probe at 0-90-180-270. They were quite repeatable at least at the same
> altitude angle, but could depend on the probe arm itself in principle.
> So we really need the cross-check with data taken with OmegaCAM.
>
> 4) Measuring the PSF anisotropy of one image we obtained a not expected
> very flat PSF anisotropy, with a FWHM between 3 and 4 pixels. I attach
> the figure for reference.
>
> Maybe you can help us in some way...
>
> Ciao,
> Pietro
>
>
>
>
>

--
Lothar Noethe    European Southern Observatory
Karl-Schwarzschild-Strasse 2,  D-85748 Garching bei Muenchen,  Germany.
Email: lnoethe at eso.org    Tel: +49 89 32006xxx    Fax: +49 89 3202362
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