Variable apertures

Posted by CraigNZ on Apr 25, 2018; 9:46am
URL: http://astroimagej.170.s1.nabble.com/Variable-apertures-tp989.html

Some questions about the variable aperture feature.

1. Is the variable aperture size constant, for all stars on a given image, of a series?  In other words, is the aperture size = FWHM_mean x scaling factor.

2. In the measurements report, column Width_xx, is this the diameter of the FWHM?  As I understand, FWHM is a radius and I guess width is then the diameter (FWHD)?

3. Using data from a recent measurement report which used 1 target and 7 comparisons across 15 images, image 1 I have:

Width_T1: 8.06 (I assume this is the FWHM diameter in pixels)
FWHM_T1: 4.05 (in pixels)
FWHM_Mean: 4.18 (average across all comparison stars)
Source_radius: 20.70 (?)
Source_radius(base):  25 (a radius in pixels, so FWHD = 50 pixels)
FWHM_mult: 1.4

I think I read Source_radius = FWHM_xx  x  FWHM_mult.  But using the data above I don't think this is right.  Assuming these are all in pixels (except for the multiplier), shouldn't Source_radius = 4.18 x 1.4 = 5.85?

4. Is the Sky_Rad(min) and (max) scaled using FWHM_mult?

Craig