Why “Post-Processing” Matters

We’re very used to having great photos delivered by our digital cameras these days. Point and shoot is the order of the day. Astrophotography is a little different, because of the tiny amount of light involved, and the specialized, custom nature of the photographic and telescope equipment.

I thought an example might indicate what I mean. The image below is of Bode’s Galaxy, M81, which is a large, bright galaxy close to us. I set up the Rigel 37 cm telescope in the Sierra Stars Observatory Network (http://www.sierrastars.com) to take five shots of M81, each one being a five-minute exposure. I then used software to combine the images, and to adjust the contrast and brightness of the resulting “stacked” image. These sorts of images are taken with monochrome cameras – or black and white – that are sensitive to all frequencies of visible light.

Here’s what the “tuned up” image of M81 looks like:


A processed image of Bode’s Galaxy, M81, created by stacking five 300 second exposures taken with the 37 cm Rigel Telescope in Arizona. This bright galaxy is relatively close to earth and can be located on a clear night with binoculars or a small telescope in the constellation Ursa Major.

Here’s one of the five original 300 second exposures, displayed more or less as it looked when it was delivered by the telescope and camera. The fine details of the finished image are in there, but in order to see them the brightness and contrast needs to be “stretched” a bit. This process changes the relationship between the light values recorded by the camera and the shade of gray displayed on the image, to show the fainter light of the outer edges of the galaxy.

M81 unpriocessed

An unproccessed frame of M81, one of five taken as a 300 second exposure without filters on the Rigel Telescope in Arizona on the evening of 15 April 2013.

I’m feeling a little more confident about monochrome images now, but I still need to update my computer for doing this sort of “Post-Processing.” My next step will be to take some images of M81 and other objects with these remote telescopes using colour filters. By shooting images with colour filters on monochrome cameras like those on this sort of telesope, you can reconstruct a colour picture in post-processing.

Copyright © 2013 David Allan Galbraith

Try Something New: Rent an Observatory for a Few Minutes

(Updated 21 April 2013)

Observatories can be very, very expensive undertakings. Some amateur astronomers have large disposable incomes and can buy and set up larger scopes – and even buy land for their own observatories. For others (I think the silent majority) using a large telescope can seem like an impossible dream.

Not any more.

It’s possible now to effectively rent a bit of time on an observatory from a distance, for either photographic purposes or even to undertake original research. Essentially, it`s astronomy time-share.

I’ve been interesting in trying this sort of thing for some time. You can find several services on-line that will let you join up and, from your home computer, direct a large telescope to do what you’d like it to do.

There are several approaches that these services take. Some are very consumer-oriented, such as the SLOOH Space Camera service (http://www.slooh.com/). SLOOH provides a lot of “added value” in astronomy, such as programmed events. Some other services allow users to take control of remote telescopes in real-time. With these services you need to be able to use a high-speed internet link and sophisticated software on your own computer to take control of all aspects of the distant observatory.

I’ve recently joined the Sierra Stars Observatory Network (SSON; http://www.sierrastars.com), which has a unique approach. The SSON consists of three different telescopes in the south-west USA, linked together with a scheduling service. The telescopes belong to educational or academic institutions, and are set up with sophisticated cameras. all that a user needs to do is to decide what to image. It’s not necessary – in fact it’s not possible – to run these telescopes yourself.

Using a very easy web-based form, users of SSON submit jobs to the telescope of their choice. The system operator cues up targets for the completely robotic observatory, and their computer takes care of the rest of it. When the images have been shot you’re sent an email message. You can then download the completed files from an FTP site. Not very hands-on, but very efficient and precise. The on-line scheduling system includes drop-down menus of thousands of celestial objects.

Membership programs like SSON can give you access to major, research-grade telescopes for a very small investment. An introductory membership package for SSON is $50 US, which gives you 83 credits. Subsequent credits are $1 each, unless you buy a lot of time, in which case the rate drops a bit. Charges are applied only for actual use of the telescope cameras – so if you take a five-minute exposure, you get charged only for that time. The rates run from about $1 per minute (actually $50 per hour) for the 37 cm Rigel telescope to $160 per hour for the 81 cm Mt. Lemon Sky Centre instrument.

There are some remote astronomy services that are less expensive per hour, but what convinced me to try SSON is the ease of submitting a request for imaging, and the fact that this is supporting research and educational telescopes.

I submitted two types of jobs to SSON to try it out this week. I sent in instructions to photograph M81, a lovely galaxy in Ursa Major, and also to try a photo of Comet S/2012 S4 (ISON), which might turn out to be a beautiful comet visible to the naked eye later this year. The observatory system ran my requests for exposure overnight between 13 and 14 April 2013. Here are two of the images taken by the Rigel 37 cm telescope, part of the SSON.


My first shot of M81, a bright galaxy in Ursa Major, made by stacking several short images taken with the University of Iowa’s Rigel telescope… from my apartment in Hamilton, Ontario. This is pretty crummy; I still have a lot to learn about processing, and longer shots are coming, too. A start, though. M81 is a beautiful and very bright galaxy. Longer, better-planned exposures and better image processing will give nicer images in the future. This was produced by stacking 9 individual frames exposed without colour filters: 3×30 sec, 3×60 sec and 3×120 sec, for a total of 630 seconds. I am trying a second run of 5×300 seconds (1,500 seconds). I hope this will reveal some of the finer, more distance lanes of stars that extend out from M81. For those who have more experience with this than I, rest assured that the FITS files that come from this system are indeed 16 bit. This was a crude stacking attempt.

I was encouraged by the first shots of M81, but I didn’t set up the observatory to make very long exposures. The longest you can shoot on SSON is a 300 second individual exposure. I’ve re-programmed the 37 cm Rigel telescope for five exposures of 300 seconds each, for a total of 25 minutes of light-gathering. I hope to have these new frames in the next few days and will post updates.

Updated 21 April 2013: Here’s a much better version of the M81 image, prepared on the 21st from the second run of five 300 second exposures and a better job of managing the post-processing:


Bodes Galaxy, M81, imaged using the 37 cm Rigel telescope on SSON by taking five 300 second exposures and combining them.

I did get a good-looking frame from the single request I sent for a photo of Comet C/2012 S1 (ISON), but I’m not 100% sure I know which object is the comet! I am looking into confirming the identity of the objects in the frame below. As of 16 April, I haven’t confirmed the location yet.

Update 21 April: Here’s the actual interpretation of my image from earlier in the week:


(Updated 21 April 2013) BLUE ARROW: The bright star in the middle of this field is not Comet C/2012 S1 (ISON) – but the comet should be somewhere nearby. In fact, it’s just at the tip of the RED ARROW. Photographed on the night of Saturday 13 April 2013 by the 37 cm Rigel telescope in the SSON. A single 300 second exposure with no filters, and with the guidance system set up to automatically find the comet.

Once I have a bit more of a handle on things like exposure times, I’ll also start shooting with colour filters. For now, I`m just trying the cameras without filters – essentially, black & white. I also have a challenge at the computer end of things. I need to upgrade my computer at home to allow running some better image processing software.Nothing can take the place of the thrill of actually seeing a celestial object live through a telescope. However, photography by remote control is also interesting, and accessible. I will be posting more updates on this process as I generate more results.

Copyright © 2013 David Allan Galbraith