Chromatic aberration

Posted on August 23, 2012

I have bought a new camera at Astronomiser. They sell astronomy modified cameras with a one year guarantee, so I am now the proud owner of a Canon 550D with no infrared filter. This should make photographing the red hydrogen alpha light from nebulae much easier.

I did some tests shots last night, and I am really amazed at how good the photos turned out. Of course, there are five years of development between the Canon 550D and my old Canon 350D. Looking through my photos I noticed something interesting. The brightest star trails had a blue line on one side and a red line on the other side: Chromatic aberration! Sure, it is not a desirable effect, but it was actually kind of cool to see something I have learned about in class. :)

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The Perseid Meteor Shower 2012

Posted on August 13, 2012

This weekend the meteor shower known as the Perseids peaked. I was out two nights in a row and took about 300 photos. The conditions were not that good, it was cloudy and the air was so humid that my lens kept fogging up. I have to buy some sort of dew heater. Anyway, guess how many meteors I caught? Two! Both of them pretty faint, and one of them even partially hidden behind a cloud. *sigh*

I used my standard 18-55mm lens at 18mm. I took a series of 20 second exposures at f/3.5 and ISO 1600. Zooming in on the non-clouded meteor I discovered something cool: The first half of it is green. Apparently this is because the meteor contains magnesium, which shines in blue-green when ignited.

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Hello Andromeda

Posted on August 11, 2012

The dark twilight-free nights have returned and I thought I would celebrate by trying to photograph the Andromeda Galaxy. It is the most distant object visible with the naked eye, and as I could barely see it from my parents’ backyard, I was wondering if my puny 18-55mm lens could do the job at all. But no try, no gain, right?

It almost took me a full hour to get everything set up. I am getting more routined but it is still a lot of work to set up the equatorial mount, find the north star in the scope, attach the wires, mount the camera, find the target and focus. At least I did not have to backtrack.

I programmed the camera to take 5 exposures of 3 minutes each, but halfway into the second exposure I realized I had forgotten to stop the aperture all the way down. I adjusted the settings but then had trouble focusing: The stars were missing. It turned out that my lens was covered in dew. I wiped it clean, focused and took a trial exposure, but the lens quickly dewed up again. The lens was so cold that the water vapor in the surrounding air condensed on it. So, as I have no heater for the lens, I took it back inside and sat with it under my shirt for half an hour to warm it up.

When I came back outside the Moon had come up and was lightening up the sky about 40° south of the Andromeda Galaxy. Sigh. Well, I took my 5 exoposures of 3 minutes each (55mm, f/5.6, ISO 800) and the lens stayed dew free. Back inside I got a first good look at the image and lo and behold – there was the Andromeda Galaxy! Sure, it was small and faint, but it was there no doubt.

I was a little disappointed to see that my mount had not tracked the stars perfectly. For a single exposure there was no problem, but I could see movement from frame to frame. Luckily it was nothing DeepSkyStacker could not handle. I tuned the levels to make the galaxy stand out as much as possible, and you can clearly distinguish the luminous core. Interestingly enough, it seems my CCD is most sensitive in the middle. Or maybe it has something to do with the lens? Anyway, may I present: The Andromeda Galaxy!

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New Year 2012

Posted on January 1, 2012

Happy New Year!

I had my first go at photographing fireworks last night. It turned out to be very fun and extremely rewarding – I think the photos look amazing! I have posted some of my favourite shots below.

Photographing fireworks is similar to astrophotography: you need a tripod and a remote timer as you want to take relatively long exposures that are timed with the exploding lights. Even though the fireworks were much closer than what I usually photograph on the sky, setting the focus at infinity seemed to work just fine. Since the light from the fireworks were so bright, I quickly learned to turn down the ISO to a mere 100 and to use an aperture of f/8. I pointed the camera in a hopefully fruitful direction, and with the remote timer in the hand I then waited for the sound of a rocket going up. That was my signal to push the button and start the exposure. As soon as the last light died out I released again, giving an exposure time of 1-3 seconds.

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First Polar Alignment

Posted on October 23, 2011

It has now been almost three months since I bought my motorized equatorial mount, so I guess it is about time I get to know it and its many controls a little better. My previous plan to just take it outside and figure out how to align it on the go turned out to be quite disastrous. I have since then been reading various tutorials online and studied it closely, testing all the controls, and I now feel much more comfortable around it. So it was with a renewed hope I carried it out in my parents’ backyard tonight.

The initial rough aligning went fine, but I had problems finding Polaris in the finderscope. Just when I was about to give up, an airplane crossed the sky right under the star allowing for an easy identification. I couldn’t see the scope’s internal reticle very clearly, so I just centered Polaris in the field of view. I then mounted my camera and pointed it at Cassiopeia. Finally, I turned on the motor and the small gears began to hum quietly.

I must have done something right, for my 3 minute long exposure of the sky showed no sign of the Earth’s rotation. :)

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