how to take photos of the stars ?

Posted: Fri Sep 21, 2007 6:37 am

Hi all hope someone can help me . I was trying to take some shots of a starfilled sky . it was pitch black and the sky was full of stars and not a cloud anywhere -a truely superb view . I tried for about half an hour and couldn't get a good shot . I was using a tripod and used every lens i have but got no good results . I found that the only way i could get a good exposure was to have 30 seconds but the shots were blurred . the camera never moved as it was on a tripod and i used a remote switch . when i used my 170-500 lens set at about 400 it looked as if the stars themselves had moved causing a blurred image . is this the case and can anyone advise me as to the best settings and lens to use

very best regards steve

Joined: 03 Aug 2005 Posts: 51 Location: SE Missouri

There are a couple of problem with shooting a star filled sky. First the earth itself is moving (Rotating), so the stars will drift. Second, changes the atmosphere will cause the postion of the star to appear to change. This is why stars appear to twinkle at night.

Special tripods that track the earths movements will take care of the earths rotation. To reduce the atmosperic effect you need to at higher atlitudes. Less atmospere means less twinkle.

Posted: Fri Sep 28, 2007 2:46 pm

Your observations are quite correct: Stars move - or better: The earth spins and the effect is, that we see the stars moving in semi-circles across the sky.

If you want to photograph a star field, with pin-point stars, you have to move the cameras with the apparent star movement. You have to mount the camera on a tlescope or trcker platform to achieve this.

For a start you should try to photograph star trails. I f you expose the stars with a fixed camera (mounted rigitdly to a tripod) for a longer period. Let's say 20 minutes or even longer, you will see, how any star paints a small track (part of the said semi-circle) onto the image. This can be a very rewarding experience, especially if you chose a nice foreground (tree silhouttes, a reflecting lake etc.), which add interest and shape to the image.

Start with a wide-angle lens to do so! A tele lens is simply not useful for that kind of photography. A tele lens (not a zoom! a zoom will show zoom creep during a long exposure and further more, shooting stars will competely reveal the optical shortcomings of any lens and zooms are on the compromised side...)

As a rule of thumb: a 15 sec. expsoure with a 50 mm lens on a full-format camera will just show pinpoint stars. Any longer exposure will start to show the star trails. You can interpolate that to other focal legthes. With a 24 mm lens you can expose roughly 30 secs. before the trails are visible, a 100 mm lens will show trails after 7.5 secs. For an APS-C sized sensor, you have to reduce these times (or focal lengthes) by the crop-factor.

If you want to show detailed images of small star fields or even the famous colourfull nebulae the Hubble Space Telescope produces, you should visit the next astronomy club in your vicinity and try to get some hands-on advices and perhaps a night with one of their telescopes, to mount your camera on.

You won't succeed with this on your own. Believe me, I have been photographing and doing astronomy side by side for the last 25 years. And still, despite having a large telescope and mount weighing in at more than 100 kg making tele photos is a challenge.

regards
René