[Comm2011] Fwd: comments on OCM1B reports (fwd)

[Edwin A. Valentyn]

herewith the comments from Dietrich on our Draft report. Most of it is 
simple to fix or reply..

Edwin

-------- Original Message --------
Subject: 	comments on OCM1B reports (fwd)
Date: 	Wed, 8 Jun 2011 06:47:44 +0200 (MEST)
From: 	Muschielok Bernard <mbernard at usm.lmu.de>
To: 	Edwin A. Valentijn <valentyn at astro.rug.nl>



FYI, Regards, Bernard

---------- Forwarded message ----------
Date: Tue, 07 Jun 2011 03:11:42 +0200
From: Dietrich Baade<dbaade at eso.org>
To: Muschielok Bernard<mbernard at usm.lmu.de>
Cc: Ewout Helmich<helmich at astro.rug.nl>
Subject: comments on OCM1B reports

Dear Bernard,

Thanks again for submitting the reports such that I could read them on the
plane to Chile.They go a long way in describing what has been done and
analyzing the results.I appreciate the clear identification of things still to
be done.

Nevertheless, I still have some questions and suggestions.I hope you will not
again take them as severe criticism and perceive them as demotivating.

Regards,

Dietrich.

*_"Technical Tasks"_*

Sect. 3:Thank you.

Sect. 4.3:The last I heard about the matter from Andrea was that he can switch
off the polling of the CCC, which would automatically eliminate the issue.None
of the readings provided by the CCC need to go into the FITS header.

Sect. 4.7:The TS speak of the integral scattered light, not its peak.I don't
expect to change the conclusion but please correct the numbers
accordingly.-Even if the phenomenon is acceptable in strength and frequency, it
would be nice to understand the reasons so that one can decide whether any
remedial measure is within our possibilities.Presumably, the embedded figure
tries to give this explanation.But without an explanatory caption I'm lost.

Sect. 4.8:Basically the same.Do we know what the worst case is?

Sect. 4.9:Ditto.

Sect. 4.10:Ditto.

Sect. 4.11:Does the description given include the latest information from Olaf?

Sect. 4.12:This is not the latest information exchanged between Andrea
Baruffolo and Claudio Cumani.

Sect. 4.13:Does the Consortium intend to provide more adequate hardware?

Sect. 4.15, ETC corrections:This requirement is in the TS.-Can the overheads
please be cast into a form suitable for communication to the survey PIs (and
inclusion in the User Manual)?

Sect. 4.16, "flow inlet":What's the unit?

Sect. 5:Thanks for continuing/extending this.Please include cross references to
the DFS report where applicable.Also, please flag those points, for which final
results are not yet available (e.g., scattered light from stars).

Item 7.2:Please add label and units to the figure (or an explanatory caption).

Item 7.4:I think, Konrad's table will benefit from a minimum of an explanation.

Item 7.6:What are the units of the 4 little tables at the end?How was TEL=6.6
determined?

Item 7.24:Is the number of AG stars still sufficient at the Galactic poles?

Item 7.28:Ditto for IA stars.

Item 7.36:You don't need to be so merciless with yourself.As far as I've seen,
there is no obvious point that will keep repeating itself.

Item 7.41:Something I may perhaps ask in this context:Do the FF lamps have a
protective glass so that pieces of exploding bulbs cannot fall onto M1?(We've
talked about this a long time ago.)

Item 7.51:What's the effect on the FF images?

*_DFS Notes_*

Sects. 2 and 4:I suspect that a signal vs. dome-FF exposure time is linear
whereas the photon-transfer curves (PTCs) are not.The latter should have a kink
or bend towards a lower slope at higher flux levels.Maybe, this is related to
the seemingly correlated noise in high-flux FFs.From which part of the PTCs
were the gains derived?For tests on the ODT test bench in Garching, we have
convinced ourselves that the gain should be derived from the steeper part at
lower flux level, which implies lower gain values (in e-/ADU).

Fig. 2 puzzles me.For a constant definition and algorithm, this should depend
on CCD temperature only.But Christoph and Olaf are telling me that the
temperature didn't change appreciably.

Sect. 5:Were the corresponding images analyzed?Can you put a numerical upper
limit on the EMC interference?

Sect. 6:The quote can be replaced with a reference to the report, which has
been submitted to the Archive and will be distributed soon.-It would be
worthwhile emphasizing here that -- as far as I could see -- xtalk seems to be
the only parameter that significantly distinguishes CCDs ## 93-96 from the
other CCDs.-Last bullet: I think, what you're seeing is the nonlinearity before
physical saturation sets in.

Sect. 9:It would be very interesting (and probably more meaningful) to repeat
the linearity analysis with point sources.

Sect. 10:Doesn't the PSF dominate anyway?-Particle events may provide a useful
alternative if the statistics is sufficient.

Sect. 11, dust:Can you provide numbers?-The scratches in CCDs ## 90 and 95 (and
others) are not new).-It would be very useful indeed to learn about the
mobility of the dust particles.

Sect. 13:Why would a new master bias be needed if bias correction is done using
the overscan pixels?

Sect. 14:The diamond structure is due to the annealing of the CCDs during their
manufacturing.This is well understood and not a new discovery.

Fig. 9:The large jump in the bias level of CCD #96 was caused by an intentional
adjustment by Olaf.

Sect. 14, deviant u band:Why would low output of the lamps lead to more
straylight?Where would it come from?

Sects. 15, 17:Why is the straylight much lower in colored-glass filters than in
interference filters?Please add your explanation.

Sect. 18, "good enough":What does that mean numerically?

Table 1:Should it be Table 18?What are the errors?Was rotation excluded from
the analysis?

Fig. 18:For other instruments, such diagrams look much more ragged.Is OmegaCAM
so muich better behaved, or is the resolution of the analysis insufficient?

Sect. 21:When I read this, I find no reason to ask INAF to try to achieve any
improvements of the IQ of the VST.

Sect. 22:Do you see any variations in plate scale?This is very important if the
results of IA are to be applied during ongoing integrations.

Figs. 19-21:What are the various lines?Normally, one would in such cases plot
the residuals from a straight line.Why not here?

Figs. 22 and 23:Please add an explanatory caption.

Sect. 22, next-to-last bulletin:Where is the number of 5% derived from?What PSF
differences are meant?What's the difference to the spatial variation shown in
Figs. 29-32?(I can guess them.But please be more explicit.)

Sect. 22, last bullet:In Figs. 22 and 23, I don't see systematic offsets just
nearly as large as 1 arcsec.So, why invoke them?

Sect. 23, "nominal physical parameters":You've lost me.

Figs. 24 and 25:Please add units and an explanatory caption.How does they
relate to the shutter timing error?

Sect. 24, "inhomogeneity of the effective exposure time":I'm not sure about the
definition used.Inhomogeneity within one exposure or between several exposures?

Fig. 26 (and all other color graphs of this kind):Please state cut levels in
the captions.-Where is Fig. 26 discussed?

Fig. 27:X: 13404 -- what does this mean?-Why is the mean value more important
than the rms?-What are the units?-Why is the mean ratio 1.00768...?Why not 35?

Sect. 26:Why are some of the older zeropoints so much better?I know that they
are invalid.But why by so much?

Sect. 32:Please remember to check the linearity from observations of point
sources.

-- 
Dietrich Baade
ESO - European Organisation for Astronomical Research in the Southern
Hemisphere
Karl-Schwarzschild-Strasse 2,  85748 Garching bei Muenchen,  Germany
Email: dbaade at eso.org    Tel: +49 89 3200-6388    Fax: +49 89 3202362


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