Preferred star selecting in DynamicPSF tool ?

[Thomas]

Hello,

regarding to some descriptions and tutorials for the DynamicPSF tool , I was wondering if it is may better not to select stars near the corners if your scope has no absolutely flat field ?

Actually I have done some tests with exposures  from an older Takahashi FSQ 106 ED and a new FSQ 106EDXIII (they have a relative flat field) selecting  stars with an Amplitude ~ 0.3 - 0.5 around the center of the image give me mostly Theta values within a range of ~ 10%  , while close to the corners the Theta values show often big differences. 

Sorry if it is described already where to select stars is better or worse ...but didn't find anything (or just missed it) ..

CS and cheers
Thomas

[Alejandro Tombolini]

Hi Tomas,
That is right, is better to select stars far from corners where could be optical defects.
See the original post of Dynamic PSF that have al lot of good information about the tool.

Saludos,
Alejandro