| Telescope | MDM 1.3m |
| Date | 9/29/95 |
| Instrument | Nellie |
| Filter | V |
| Exposure Time |
25 sec |
| Other | unprocessed |
Problem:Often on this run, bias ramping structure would show up in low level images such as standard star frames. The ramping structure varied from image to image and was not always present. Although this looks terrible, the bias level is only varying by a small amount (2.5%) which is why it only showed up in short exposures with low signal. |
Fix:The images often can be fixed during the processing because the same structure usually shows up in the overscan region. Subtracting out a fit of the overscan region frequently works well. The cause of the problem, however, lies within the electronics, so checking for things like loose cables might also be a good idea. |
a plot along the overscan region showing the same ramping
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