Dependence of Image Quality on Sky Position

Dependence of Image Quality on Sky Position - August/September 1998

The figures below demonstrate the image quality that observers can expect from the IRTF telescope at various positions on the sky. Two sets of images were obtained on 08 August and 11 September 1998, by D. Toomey and W. Vacca, using a K'-band filter and the Shift & Add Mode of NSFCam at the 0.055 arcsec/pixel plate scale. Each image is the result of stacking a large number (typically about 20-30, although in some cases as few as 13, and in others as many as 70) of 0.1s exposure frames. Thus, "seeing" (both dome and atmospheric) effects should be minimal and these images therefore provide a measure of the true image quality delivered by the telescope. All images have been rotated so that North is up and East is left. The red circle has a radius of 0.5 arcsec and is centered on the highest pixel. The radial profile plot associated with each image can be found by clicking on the image; it presents the azimuthally averaged intensity - normalized by the value in the highest pixel - as a function of radius. The dotted line in the radial profile plots represents the intensity of an ideal PSF for the IRTF mirror.

Note that not all observers should necessarily expect to obtain point-spread-functions as good as those presented below: the image quality obtained during exposures substantially longer than 0.1s will be the result of the convolution of the images below with the effects of dome and atmospheric seeing; this will result in profiles that are significantly broader than those presented here.

Three sets of images are available:

September 1998 - Images taken at zenith angles = 30 degrees
September 1998 - Images taken at zenith angles = 60 degrees

An expanded view of each image, as well as radial profile plots, can be obtained by clicking on the images.

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