Merlin66
26-01-2012, 08:10 PM
Well, I never give up....
Without boring everyone (again!) I've put the detail in the attached doc files.
Here's the executive summary:
1. All stars recorded on the one frame have exactly the same FWHM.
2. Depending on the exposure and the gain/ white point settings the apparent size of the star image can be altered. Faint stars can appear smaller than the FWHM.
3. When the brighter star image satuarates the chip, the size of the star image can grow well beyond the FWHM.
This is summarised in the attached graph.
These factors are important in the field of Photometry, where eventually I found the answer.
Without boring everyone (again!) I've put the detail in the attached doc files.
Here's the executive summary:
1. All stars recorded on the one frame have exactly the same FWHM.
2. Depending on the exposure and the gain/ white point settings the apparent size of the star image can be altered. Faint stars can appear smaller than the FWHM.
3. When the brighter star image satuarates the chip, the size of the star image can grow well beyond the FWHM.
This is summarised in the attached graph.
These factors are important in the field of Photometry, where eventually I found the answer.