Thu, 09/06/2018 - 22:11
I use MaxIm DL to generally capture and perform photometry on them after standard calibrations.
I use a QSI532 camera which operates at 16bit
I found that when I saved images as 16bit I would often get a central dark spot on the brighter stars, particularly when I used other software to view the images. I found that finally saving them as ieee float with MaxIm solved this problem.
Question is it ok to carry out photometry on images saved this way? I seem to recal I got slight differences when I compared results.
Regards,
Eric
Hi Eric,
Saving in floating point is fine, and the photometry should be good. It may differ slightly from photometry done on a 16-bit image, depending on whether it is a raw image straight from the camera, or whether you have calibrated it with darks and flats.
In the other method, saving in unsigned 16-bit format, some systems don't handle the FITS standard very well, especially for display/viewing purposes. I've never had any problems with VPHOT or MaximDL in this regard, so I can't say anything regarding central dark spots. That sounds like a truncation issue (obviously avoided with floating point).
Arne
Hi Arne,
thank you for your reply which eleveats my worries.
The images are fully calibrated and I find viewing them with MaxIm fine. It's when I use Astrometrica and possibly AstroImageJ, I can't remember exactly which other software.
Knowing now that the photometry will be ok was the main issue. I already do a lot of asteroid work and I'm moving across to variable stars and exoplanets.
Best wishes,
Eric (UK)