The size of the available field of view is limited by the movement of the M6 mirror, which in turn is limited by the size of the dichroic. As a result the available field of view is a circle of 30 arcsec radius, centered on the wave front sensor (WFS) center (which corresponds to the reference star).
The size of the camera field of view depends on the chosen pixel scale (see tables below).
It is possible to move the M6 mirror in order to centre the camera field of view anywhere within the available field of view. Remember, the M6 mirror is on the bench and so it is completely independent from the telescope control.
For the example shown in the figure, the camera field of view should be centred on the science target by adding an offset to the M6 mirror. Note that the adaptive optics correction performance decreases with distance from the WFS centre.
|Pixel scale||Field of view||Recommended purpose|
|100 marcsec/pixel||25.6" x 25.6"||Search for faint object,
Mapping of large areas
|50 marcsec/pixel||12.8"x 12.8"||General purpose|
|35 marcsec/pixel||8.5"x 8.5´||J, H band,
under excellent seeing
|Filter||Central wavelength [µm]||Resolution||Transmission [%]|
|Broad Band Filter||Central Wavelength
|Bandwidth (µm)||Transmission [%]|
|IR filter||magnitude||Additional condition|
|J||20.6||50% flux within 0.50"|
|H||20.4||50% flux within 0.47"|
|K||19.9||50% flux within 0.31"|
We have the usual Nicmos III remanence effect using SHARPII+. To avoid that, wait images have to be taken between different positions of the chopping mirror. This time lost must be included in the time budget estimation.
See, for more information, the September 96 Messenger (p.39) issue about Comic camera performances.
|Pixel scale||Field of view||Spectral Band|
|100 marcsec/pixel||12.8"x12.8"||L, L', M|
|35 marcsec/pixel||4.5"x4.5"||J, H, K', K|
|Line||Wavelength [µm]||Bandwidth [µm]|
|Br alpha continuum||3.757||0.386|
|Broad Band Filter||Central Wavelength
See also51-Pegasus image.
|Point Source||Extended Source|
|mJ = 13.0||30||9.3|
|mH = 12.5||30||9.4|
|mK = 11.8||40||9.0|
|mL = 10.7||50||8.6|
|mL' = 10.1||50||8.2|
|mM = 7.7||50||6.3|
Note that higher limiting magnitudes may be reached with careful flat-fielding.
Note: we experience non-uniform background due to the relay mirrors/dichroics.
We should correct this by March 97.
|IR filter||Zero point (mag)|
Integration time in L and M band:
The COMIC camera is optimized for L and M band. In these band, integration time is strongly dependent on the background level.
Comic has a deep well capacity of about 64500 ADU. Observers will have to avoid that the level background + science object reaches 64500 ADU.
Typical background limited integration time on the telescope are about 7s in L band and 1s in M band.
Comic Camera is equipped with an antibloomming CCD. Antibloomming system permits to get saturated or very intensive pixels that do not give any consequence on the sensitivity of the other nearest pixels.
This allows to observe the close neighboring of very bright object.
Pattern in the background:
Due to gratings disuniformities on the ADONIS bench, we are suffering of a non-uniform instrumental background. This problem has been partially corrected changing the dichroic in August 97. The patterns won't be the same if you move the ON/OFF mirror. Due to the instability of the background in L and M band, sky subtraction has to be done using the ON/OFF fast moving capabilities, even if different patterns will appear in the images.
One way to get rid of that problem is to be able to evaluate the level of these patterns and subtract them while processing data in your home institute. Therefore, we recommend to do an offset of the telescope and take a few images on the free sky near your object and that for each configuration of the ON/OFF.
This procedure takes no much more than one or two minutes for each object. Please contact the support astronomer to get more information on the faisability of your program proposed with this camera.
Choice of the lens scale:
Two different lens scale are available with COMIC:
- 35 mas/pixel for J, H and K band
- 100mas/pixel for L, L' and M band.
Coatings for lenses have been optimized respectively for each IR band.
So, one should not observe in K band with 100mas pixel scale.
Images are taken by the camera and displayed after Quick Look Analysis on a control screen. Adocam Computer stores raw or processed data in FITS format.
ADOCAM computer controls:
A thorough description of the ADOCAM software is given in the COMIC User's Guide which is available as a gzipped postscript file (860Kb).