Problems with DynamicPSF with synthetic star profile

[mcgillca]

Hi - not sure if this is a bug, or something unusual I'm trying to do.

I've been trying to understand an unusual aspect ratio pattern in my telescope (an 8" RC). I think its because the primary is misaligned, causing coma across the field.

In an attempt to test this, I've created some synthetic star profiles using ray tracing. When I import these into PixInsight and try to use the DynamicPSF tool to analyse the aspect ratios, PixInsight stops responding.

I've included a small portion of a fits file with just 1 synthetic star, and this exhibits the problem.

Any idea what I'm doing wrong? I have the same problem in CCDInspector - it does not recognise the stars.

Thank you,

Colin

[Juan Conejero]

Hi Colin,

Bug confirmed. The problem is that this image has no background, i.e. the background is zero. A simple workaround is to apply the following PixelMath expression before using DynamicPSF:

$T + 0.005

Now DynamicPSF will fit your synthetic star without problems. FYI the parameters are:

Gaussian PSF
B .......   0.005220
A .......   0.912878
sx ......   1.52 px
sy ......   1.39 px
FWHMx ...   3.58 px
FWHMy ...   3.27 px
r .......   0.912
theta ...  +0.00 deg


I'll try to fix this bug ASAP. Thank you for reporting.

[mcgillca]

Thank you very much, Juan.

I generated this using an Real*4 fortran array, which did have a non-zero floor, but the results seem to get scaled between 0 and 1 - not sure if this is the result of the CFITSIO routines I called, or something that happens when PI reads this sort of array?

Either way, I'll see if I can fix it by reducing some of the values in my array so that it gets a non-zero value in most places, or if not, I'll use the PixelMath tweak you suggested.

Thank you again,

Colin

[mcgillca]

Thanks, Juan - introducing just one pixel with a lower value preserved the non-zero floor elsewhere in the image and this has done the trick, for both PI and CCDInspector.

Colin