Affiliation
American Association of Variable Star Observers (AAVSO)
Sun, 06/17/2012 - 21:36
Hi:
I'm trying to figure out why all the images I uploaded into VPHOT for 06-07-2012 are all white (or nearly so). This is the first time I did the dark/flat processing in IRAF, so something may have happened I'm unaware of. However, the images look fine on my end when displayed in DS9, Fv, and IP4WIN. Thanks.
Jeff
hjg
Please show us your images. An image is worth 1000 words. We may find some interesting values in the FITS header (BZERO and BSCALE come to mind quickly), or something similar...or who knows?
Thanks in advance.
Here is the same image as I show it in DS9 and what it looks like in VPHOT. Thanks again.
FITS Header
Thank you for the FITS header. Off the cuff I don't see problems.
Could you make the full FITS file available? The jpeg versions do not tell me about the actual pixel values in the FITS image.
Thank you in advance.
[quote=hjg]
FITS Header
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[quote=hjg]
FITS Header....
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Your CCD is an ST-402, which comes with a copy of CCDSoftV5 camera control software. Why are you using Nebulosity to acquire images?
Interseting gain value. Did Nebulosity put that in there?
This is not needed for a monochrome CCD. Nebulosity again?
I recommend you use CCDSoftV5. If you couple that with top-level automation software...then you can run the rig unattended...more productivity.
Looking forward to the FITS file.
I'll take a look into CCDSoft. Thanks again.
Thank you for the FITS image. See attached screen shot (and text/annotations)
You have optical/focus problems of a sort that will make photometry difficult, and may confuse most aperture photometry software. Your star images have a reatively tight core, but a diffuse halo that is over 1.6 arc minutes in size on the sky. I strongly recommend you improve optical performace and/or focus. With this current setup you can only do photometry on very sparse star fields...or you will have light from neighbors bleeding into your measurement aperture...not good.
You have scaled your image so that the sky background is 0.22 ADU, and the brightest pixel in the brightest star is ADU 8. VPHOT probably expects an ADU range of a typical 16 bit CCD....from near zero, up to 65,535. Your tiny ADU range is probably confusing VPHOT.
Were you aware of these problems?
Minor point: large dust donut visible.
Minor point: saving a single image as 32 bit is overkill, and just takes up more disk space and Internet bandwidth. I recommend 16 bit unless you start stacking many images.
I'm happy to help you improve your rig and technique. We can continue in this forum, or privately.
Thanks for the info. I am aware of some of issues you bring up. The small dynamic range may come from the way IRAF applied a normalized flat. I don't see this problem when I process the images in MPO Canopus.
The focus issue is inherent in the optical system, which is a lenless Schmidt. The remaining uncorrect spherical aberration results in the halos, and obviously limits the performance to fairly bright stars in non dense fields. On the other hand the wide FOV--nearly 60 minutes, makes finding comparison stars easier. I built the system as an experiment to see how it would perform in my very light polluted skies here in Southern California where the limiting naked eye magnitude is around 3.4.
At best the system when used near the zenith can deliver accuracies on the order of 0.02 mag., if I process the images in MPO or AP4WiN. This was an attempt to automate the process using IRAF that Arne loves so much. More work is needed. Thaks again for you help.