[Aavso-photometry] RE: Urgent Depth Question

[Arne Henden]

Brad, be sure to tell Maxim/cyanogen about the error.
Obtaining accurate midpoint time for stacked images is actually
non-trivial.  If you have any kind of rejection algorithm, that
modifies the center time.
Arne

Brad Walter wrote:
> Bill you have hit on a point that causes me some embarrassment. There is
> a problem with the times reported by Maxim/DL for the combined images.
> I discovered that, when combining a series of images in Maxim/DL, the
> program sets a time for the combined image equal to the time of the
> series member selected as the reference for the combination, rather than
> the earliest member. It also sets the exposure duration as the sum of
> the exposure durations of the images being combined. Then the photometry
> tool in Maxim/DL  sets the observation time for the corresponding
> photometry data table record as the arbitrarily selected image time plus
> half the summed exposure time saved in the header for that combined
> image file. In my case there were 11 x 40 second exposures so the
> exposure duration in the fits header of the combined file was 440
> seconds, and the exposure time was shown as the time of the reference
> image for the combination plus 220 seconds.  This is the same procedure
> that maxim/DL photometry uses when reporting an un-combined image, and
> it is correct for an uncombined image. 
>