| Telescope | Michigan Dartmouth MIT 2.4m Hiltner Telescope |
| Date | 11/3/96 |
| Instrument | Templeton |
| Filter | V at z=0.45 (corresponds to I) |
| Exposure Time |
1200 s |
| Other | Image is processed with flatfield and bias. |
Problem:Interference fringing is obvious in this image. This effect occurs due to multiple reflections internal to the CCD substrate or between the supporting substrate and the silicon. It is usually most visible in the I band, due to the abundant night sky emission lines in this wavelength range. If the fringing is very bad, it can even cause larger scale gradients in the image (on the order of half the CCD diameter), i.e., after the basic bias and flatfield correction, there is residual large scale structure in the image. This can only be corrected by using fringe flats. |
Fix:This effect cannot be avoided. It can, however, be corrected for later in the calibration with either the help of so-called fringe flats one has to take during the observation run, or by using some specific computer algorithms (which work best in non-crowded fields and with no extended objects). |