Lesson Learned

Posted on February 19, 2011

I am spending a long weekend at my parents’ summer house in Bønnerup, Jutland. It is a small and fairly isolated town near the sea, so it is wonderfully dark at night. The summer house has a balcony that points straight north towards the sea, and I have therefore appointed it as headquarters for my star trail experiments. Since shooting long star trails takes hours, it is nice to be able to go inside while the camera is working. Especially when it is freezing outside.

Last night offered a few hours of clear sky. Since there is much less light pollution here I decided to try a long exposure with low ISO and a not-so-big aperture. I pointed my camera at Polaris, focused and started the exposure. During the next couple of hours I spend most of the time inside, once in a while checking that there was no clouds drifting in and that the batteries were still working. After two hours I ended the exposure and transferred the image to my computer. But what I saw was very disappointing.

The image was overexposed, but I had expected that. I had saved the image using both RAW and high resolution JPEG. While the RAW image was saved about two hours after I started the exposure, the JPEG image was saved just a few minutes after. Both images insisted that they had only been exposed for 474 seconds, yet the star trails seemed much longer than that. I have no clue what happened.

The trails were very faint, so I guess the ISO was too low. Also, clouds must have drifted in while I was looking away, because the bottom third of the image was all hazy. Finally (and most embarrassingly) I had forgotten to clean the lens, so there were a few smudges on the image.

I used Photoshop to lower the exposure and increase the contrast in an attempt to make the faint star trails stand out more. Though the length of the star trails is cool, the final image is pretty crappy. But I have learned my lesson: next time I will take many short exposures and combine them.

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Orion and Star Trails

Posted on January 2, 2011

Last night at 22:00 I packed my equipment and walked to a field near my parents’ house. It is big and dark and an excellent place for taking astrophotos. My new tripod was a dream to work with and I even managed to find focus right away.

For the first half hour the sky was crystal clear, and I took a series of images of the Orion constellation. I used the noise reduction function in my camera, which means that every exposure took twice as long (i.e. 10 seconds for the exposure of the sky and then 10 seconds for a dark exposure), but since all my exposure were relatively short, I figured that was the easiest way to go. When I came home I used Photoshop to stack the images. Although I have never tried that before and was a bit unsure of what I was doing, I think the result looks nice. You can even see the Orion Nebula.

I also took a few images of Cassiopeia but in that part of the sky, the star trails made it too difficult for me and my humble stacking skills to make the constellation stand out.

Finally I pointed my camera at Polaris. I have always liked the long exposure astrophotos that show how the stars move in circular trails around the North Star. I set the exposure time at 10 minutes but had to cut it short since clouds started drifting in. Still, I managed to completely overexpose the image.

After a lot of tweaking in Photoshop (I have no idea what I did) I succeeded in bringing out the star trails. They are a lot shorter than what I had in mind, though. The next time I try this, I should probably take a lot of short exposures over a period of an hour or so with the camera pointing in a fixed direction and then combine them.

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Clouded Moon

Posted on December 15, 2010

The Moon and Jupiter are currently crossing the skies together. I thought it might be an interesting challenge to try to get a sharp image of them. I have tried before without luck, the brightness of the Moon makes it difficult to get a good image of its shape. The fact that my lens has a field of view of minimum 22° does not make it easier, since the Moon has an angular diameter of only 0.5°.

When I came outside I discovered that a thin patchwork of clouds were covering the skies. I decided to take a few shots anyway. Because I am still very unsure of whether I am focusing right or using the right exposure, I tried to use a method called bracketing. It simply means that you take a photograph using the setting you think is correct, and then also take a number of photographs where you make small adjustments in some of the settings. I took about 30 photos with various combinations of ISO speed, shutter speed and focus, and I think the result was surprisingly nice.

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My Debut

Posted on December 13, 2010

Last night was the first clear night in weeks. Although I have not bought a tripod yet, I could not miss the opportunity. I live in Copenhagen where there is so much light pollution that you can barely see any stars, so I packed my equipment and went north to visit my parents. They live in Hillerød and although light pollution is also an issue there, their relatively dark back yard made a fine place for my first experiments.

I do not have that much equipment to play with yet, so I had to make do with my Canon 350D camera, my remote timer, my dad’s old semi-broken and thus highly unstable tripod and a very red chair. I also brought extra batteries for the remote control (turned out to be a good idea) and a pair of binoculars to keep me entertained when the camera was working.

I first went out at around 20:00. The Moon was still up and my primary goal was to get used to the equipment. I tried to use the Moon to focus my camera on infinity, but that did not work out very well. The image on the right is supposed to look like the Pleiades. Instead I managed to focus by manually adjusting the focus and taking test exposures. I then took a series of photos of the Pleiades and Orion with a focal length of 55mm and a shutter speed of 20 seconds. It turned out that the field of view was too small for that combination to work, so all the stars came out elongated because of the Earth’s rotation. I did manage to take one picture that I like. By a mistake I used a shutter speed of 9 seconds which made it the only picture free of field rotation. And yes, the bright spot is Jupiter. :) I think Uranus is also in the picture, but it is so faint that it looks like a normal star.

Before I went inside I noticed an airplane crossing the sky and I decided to capture it in a long exposure. The airplane’s lights were blinking periodically so the result was a funny bubbling line.

At midnight I went out again. The Moon had set and I was hoping to see some meteors (after all, the Geminids was going to peak the following night). I programmed my camera to take 40 shots of 20 seconds each and pointed it at Gemini. When I came back I learned the importance of tightening all screws: the camera had slowly tipped back and was pointing straight op. Stupid old tripod. ;)

I began to take a few pictures of the Pleiades but then clouds started drifting in. They ended up covering the whole sky, so I went back inside. I did manage to get a couple of decent shots of the seven sisters, though. :)

All in all I had an awesome night! I learned a lot and I cannot wait to get out there again.

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