Some days are Flat out and Dark. But I'm not Bias
Wednesday, September 22, 2010 at 8:33AM
Pete - Admin in Calibration, Remote Telescopes, darks, flats, telescopes

What can I say about your average Calibration frame? They are sorta dull to look at.

On my back yard Meade i would take a few darks and the odd Bias on rare occasion, Flats? Rarely, yet here I am at my iTelescope workstation, monitors spread around me, On one I'm trying to keep an eye on the systems and on top of things, and on the other monitor  I have gigabytes of fresh calibration data to plow through! Its a living.

Can you imagine what is involved in gathering these vital data files from all the iTelescopes spread across the globe? Its no picnic. But it has to be done. Often.

As the sun sets at our remote observatories they roll open to collect their daily quota of skyflats, then later maybe a few hours of Darks and Bias if the roof or domes are shut, then again more skyflats at dawn. Your telescopes never really sleep at all.

We actually have a very sophisticated AutoFlat (AF) application running on all the telescopes. NO, you cant find it at the local store, it was written just for us and our rather heavy duty needs.

Lets add it all up.

Our sample remote telescope, lets say T14 in New Mexico, will take a set of Dusk flats later today before it opens to the members. It may be a set of Red-Green-Blue, Clear or Ha-SII-OIII, and if the scope is set up for science duties it will also have a set of U-V-B-R-I onboard its filter wheel as well. So that can be up to 12 filters to run through before its too dark and the stars pop out. More often we spread out the collection of various flats during the week.

The T14 AF application wakes up and asks a few questions every afternoon and pre-dawn, it has a binary conversation with the other iTelescope software sharing its hard drive. What time is it? Where is the sun? Is the roof open yet? Do we need a special filter order today? Do I have to send or pickup any new files? It then swings into action and takes charge. It slews the T14 telescope to the best part of the eastern sky, it opens its CCD eyes and has a little peek.

Is the sky too bright? Then AF will wait a little while longer and carefully countdown as the sun dips ever lower towards the western horizon. If its too dark it must be cloudy and the roof will still be closed. So AF goes back to sleep for a while.

But when AF finds the sky is bright enough to make a start it will trigger a script in the ACP Control software. It Chills the camera, selects a filter set and begins to fire exposuress at an automatically corrected duration. This flat frame image is capturing the unavoidable optical gunk that collects in a telescope that works hard for a living.

Dust is the enemy. Tiny dust motes and other particles that penetrate to the filters or CCD will show up as dark donuts of various sizes on the white flat field images the CCD collects. These flat frames will 'cancel' them out of a user's image during realtime calibration and post processsing stages.

So T14, our sample system has now gathered between sunset, during the night and finally at dawn all its filtered flats plus if the roof is closed, a wide selection of dark frames at five standard exposure times, 60-120-180-300-600 seconds. The darks have been recorded at both 1x1 binning and 2x2, as have the bias taken along with them. Three of every flavour.

This calibration data, from each of the remote telescopes on the iTelescope system is then automatically collected by AF, named, compressed and sent via the internet to make its way to the correct folders in my 'Darkroom' workstation. About 7 Gb of raw calibration data files. All packaged and ready for inspection and conversion into master calibration frames.

The number of files I have to chew through visually to check for quality can get a bit mind numbing.  As its final task for the day, AF takes the fresh master files from my workstation and transmits them back the way they came for installation on the telescopes and into the member data server for your use when needed.

Things can and do go wrong at times. But your results are worth the work. Black Coffee helps too :)

See? At iTelescope your remote telescopes are never too idle. Thanks AF,  I for one appreciate you!

Article originally appeared on Remote Internet Telescope Network - Online Imaging & Telescope Hosting Service (
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