On the Difference between Seeing and Image Quality: When the Turbulence Outer Scale Enters the Game
Abstract
We attempt to clarify the frequent confusion between seeing and image quality for large telescopes. The full width at half maximum of a stellar image is commonly considered to be equal to the atmospheric seeing. However the outer scale of the turbulence, which corresponds to a reduction in the low frequency content of the phase perturbation spectrum, plays a significant role in the improvement of image quality at the focus of a telescope. The image quality is therefore different (and in some cases by a large factor) from the atmospheric seeing that can be measured by dedicated seeing monitors, such as a differential image motion monitor.
- Publication:
-
The Messenger
- Pub Date:
- September 2010
- Bibcode:
- 2010Msngr.141....5M