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Old 24-09-2014, 11:25 AM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
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Certainly looks like that is on the right track Peter - the Hutech made a huge difference.

The FWHM result is a bit surprising - I can think of no reason why increasing exposure should change star shape on a linear CCD (it will when the stars reach saturation, but CCD inspector throws them out). Maybe the increasing background level is upsetting the FWHM calculation. The contrast ratio is reducing with longer exposures (I think it should increase) which may suggest that the data has not been dark calibrated - that could explain the change in FWHM with increasing exposure. Perhaps rerun with dark calibration if it was not done - I think that the "Reduce" checkbox lets you do that if it has not already been done elsewhere. If you don't have darks for those exposures, maybe try something like the dynamic PSF in Pixinsight (do you use PI?).

you could use multiple exposures to gain a bit of dynamic range if saturated stars bother you - I think that Rick posted some details on this process (again in PI).

regards ray

Last edited by Shiraz; 24-09-2014 at 11:46 AM.
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