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Data processing of VST/OmegaCAM data: FAQs - Knowledgebase / Data processing and analysis software resources / data processing FAQ for each instrument - ESO Operations Helpdesk

Data processing of VST/OmegaCAM data: FAQs

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Data processing of VST/OmegaCAM data: Frequently asked questions

  • Are there any known problems with OmegaCAM data?

Answer: The quality control group keeps a list of know problems at

  • Where can I download the OmegaCAM pipeline to reduce my data?

Answer: ESO does not offer a data-reduction pipeline for OmegaCAM. The ESO OmegaCAM pipeline is exclusively used for quality control, i.e. it processes data to monitor the instrument's proper performance, and does not produce science-grade data products.

  • My data shows an extended, bright feature - what can this be?

Answer: It is likely that some reflections from the moon are affecting your data. These reflections are unpredictable and have been found to be more frequent when the target is closer than ~40deg to the bright moon. You might also want to check: 

where we provide a collection of example OmegaCAM images, illustrating some special data features.

A comprehensive description of features visible in OmegaCAM detectors can also be found in the quality control web pages.

  • A number of OmegaCAM filters show vignetting in their central regions. What are the causes for this and what are the dimensions of these features?

Answer: A number of OmegaCAM filters are not monolithic, but consist of four segments (each covering 8 detectors) that have a central cross-shaped support structure. This support creates a vignetting effect that will be visible in 20 detectors which is significantly larger than the gaps present between adjacent CCD's. The affected filters are: B_JOHN, V_JOHN,
H_ALPHA,  NB_659, NB_852,
and the effect looks like this (for the H_ALPHA filter):

When using these filters, one needs to take the vignetting into account when chosing a dither pattern. A conservative accounting for the total size of the vignetted area can be summarized as:


North/South Vignetting

East/West Vignetting


1405 pixels (300 arcsec)

1405 pixels (300 arcsec)


1430 pixels (306 arcsec)

1410 pixels (302 arcsec)


1418 pixels (305 arcsec)

1407 pixels (302 arcsec)


1418 pixels (305 arcsec)

1407 pixels (302 arcsec)

  • Some OmegaCAM detectors show an odd central stripe in the bias and master bias images.

Answer: Two OmegaCAM detectors (ESO_CCD_#68 and #90) show a centrally elevated structure in their bias frames. This structure, however, remains constant with the underlying bias level and can be easily corrected.