how to photograph asteroids

Started Jun 9, 2006 | Discussions thread
Harry J Regular Member • Posts: 121
Re: how to photograph asteroids

Erhan,

it's good that you are planning this early. I will go though my experience on both photographing meteors (shooting stars) and on the other hand quite an interesting thing - photographing asteroids.In both of these you will be phtographing nothing else but a spot of light with shooting stars moving fast and asteroids typically slow.

First the shooting stars. In the time of film I burned dozens of film rolls and got only a couple of these on the film. It was expesive. In the digital time it is easier as one can "burn film". It will take a while to go though them all. On the other hand you can speed up this proccess by watching the same area with your eyes, and recording the time and brightness of the shooting stars.

I think the main point you need to remember in photographing shooting stars is that they are fast. This means that the trail crosses many pixels, and the light coming to a single pixel is very short. So quite a bright shooting star will produce quite a faint trail. For this reason the faster the lens the better - so you get more "beams of light" per pixel. Remember that with a faster lens you will also increase the brightness of the background. So this is a trade off. The background will limit the length of your exposures, which I would keep down to 30sec - 2 min anýway.

Shorter focal length helps you also as the shooting star stays longer in one pixel of the image (relative movement along the CMOS chip is slower). The thing you pay for going to a very short a focal length is that the trail of the shooting star is shorter. Also at least in Finland the combination of more Perseids will bring up also may satellites.

Do you need a mount to track the stars? If you want point like images of stars then yes. I have not. I have pointed my camera to fields close to the pole star (quite high up in Finland) and the stars stay quite pointlike. Also the polestar is at a good distance from the radiant of perseids.

But you need a sturdy shakeless tripod and a timer/computer control/remote control. (Note that the computer control cannot expose in bulb mode). Also lifing the mirror up befoe exposure is useful - read the camera manual for details.

Then about the multiple exposures. I think it was a 1DMarkII I used last year for Perseids. There was one fumble. I was taking something like 30 or 60 second exposures. One after another. After some time the camera buffer became full and the sequence was then braked by the chip been read. Also if you have noise reduction set on - leave enought time to empty the buffer/do noise reduction immediately after each image. This will make your set more homogenous. And if you see something odd in the sky such as a slow moving fireball, you could get a series of pictures on that.

The hit rate I had with a sigma 3.5-105 f2.8 was something like 4 shooting stars in a couple of hundred frames over 4 hours of darkness.

So that it is for shooting stars. Then about (nonspacecraft) asteroid photography. This requires usually at least a mount to track the stars. The bightest of the asteroids (Ceres, Vesta, Pallas, Juno) are visible with binoculars and are easy to photograph with a 100 mm lens mounted on a telescope. If you take another photograph later the same night or the next night you can see that it has moved. It's quite cool.

Then there are these Near earth asteroids that just miss the Earth. A couple of years there was one quite bright one called 2002 NY40. It was amasing to see it moving against the stars. It was so fast! In a five minute you could get quite a long trail with a 300 mm lens. This lens had to be mounted on a telescope.

Enjoy your meteor photgraphy. You may want to have a mock trial run before the actual perseids nights.

Harry J

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