CFHT, Instruments, Imaging, AOB, Instrumentation

The CFHT Adaptive Optics Bonnette :
Preparing your astronomical observations

Although we've done our best designing the AO bonnette, it will not provide diffraction limited images over the whole sky. The principles of adaptive correction impose theoretical limits to what is achievable by an AO system. The correction will get worse as :
- the seeing gets worse
- the imaging wavelength gets shorter
- the magnitude of the guide star increases
- the distance to the guide star gets larger
If you want to have a quick look on how the performance behaves with wavelength, guide star magnitude and seeing (excluding the distance to the guide star), you can follow this link (in this link, the seeing is quoted in r0. r0 is proportionnal to 1/seeing, and a seeing of 1 arcsec corresponds to a r0 of 10 centimeters. Typical free atmosphere seeing is about 0.5 arcsec at CFHT).
If you want to treat a particular case, or want to have an idea of how the correction degrades with the distance to the guide star, use the interactive forms below.
Enter your parameters (Please note the parameter range quoted [min,max]) :
Note : This interactive feature is not available at the Starsbourg www server.

Seeing at 0.5 microns (FWHM in arcsec) [0.26,1.03]
PSF Wavelength (microns) [ > 0.3]
Guide star R magnitude [10,18]
Distance to guide star (arcsec) [0,90]
PSF sampling (pixel size in arcsec) [typically 0.02]
When you are done, press here :
Expect up to 2 minutes delay for the PSF computation.

The PSF image will be a 128x128 image, therefore showing a field which side is 128 times your requested pixel size. This program uses pre-computed images at selected guide star magnitudes, seeing values and guide star to object distances to obtain your image. The attenuation of the modulation transfer function brought by anisoplanatism effects has been computed separately, assuming a complete decorrelation between anisoplanatism effects and the other sources of image degradation. The pre-computed PSF were obtained by numerical simulation, using a code developped at CFHT by F.Rigaut. It includes a realistic model of the atmosphere, close-loop, wavefront sensor and bimorph mirror.
Created 10 November 95.
Page maintained by Jean-Luc Beuzit.
Please send comments to :