La Silla - Science Operation Department
Fringing in the images taken with EFOSC
The fringing pattern:
This page contains fringing pattern for EFOSC2 through the filter i#705. The image has been created the following way:
We took I-band images of different fields (spread over one night) and corrected for bias and flatfield.
We flatcombined the images.
We computed the average value and subtracted it from the image.
So far we do not know how variable the pattern is. The intensity varies a lot, but the shape seems to be quite stable. We plan to do more measurements in the next future to clarify this point.
September 2003 (fits.gz file, 4.1M)
How to correct for fringing?
Fringing is an additive pattern, hence it has to be subtracted from the images after the pattern has been scaled to the actual value of the fringing in the image.
Measure the difference between high and low level in some well defined parts of the image (preferably at positions with large fringing).
Measure the difference between high and low level in the same positions in the fringing pattern.
Compute the scaling factor by dividing the two values and scale the fringing pattern accordingly.
Subtract the scaled fringing pattern from the image.
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Last update: Nov 17, 2004, Linda Schmidtobreick