Stars

[AdamBomb]

Hey Guys, Whats a good shutter range or particular speed for capturing stars to their full potential, with out them blurring from moving. I know I could just go out there and try, but it's about -11 (F) tonight, and I'm JUST wondering. Post examples if you like. And let's just base this on, there is NO ambient lighting coming from anything else.

 

[SlimPaul]

It's best to set the aperture between f/16 and f/22. The shutter speed doesn't matter. Just make sure to lighten the image up properly. You will need a tripod.

 

[Torus34]

Stars are about as close to true points of light as you can get. There is no 'diameter' or 'width' to them. While they appear bright in dark skies, there's actually very little light involved. They appear bright because of the contrast. And that's where the trouble lies.

Even given a very fast lens, say f1.4 or so, it takes time for the recording medium, be it film or digital, to capture an image. With lengthening time, the image will be captured and will also 'flare', or broaden so that you can actually see the color of the light. [Stars have a range of blue-white through white to yellow, orange and on to a rich red.] But meanwhile the earth rotates, causing the image of the stars to 'trail' into arcs.

So it's a give-to-get situation. An exposure short enough to capture an image but eliminate trailing will produce anemic pinpoints that make almost no impact. Longer times will provide more robust images -- and trails.

The only way to 'beat the system' is to use a motorized mount for the camera which compensates for the rotation of the earth. You either make one or purchase a telescope or telescope mounting which contains a drive. If you're handy with tools, a simple drive is not all that hard to make, though it's not in the same category as, say, making a workbench.

 

[ShutterSpeed]

the only way to beat it, really, is to take the picture from space. Got any Nasa Connections?

Have access to the Hubbell?

This is a challenge everytime I go out. The biggest key to a great picture would be to have a good location. You'll need to frame the stars with a landscape or something.

If you have the chance, get outside of the city and away from city lights. Kind of easy here in the south - but not so sure about MI.

I still have yet to find a good place outside of town to get a good shot - but as it warms up, I will be more motivated to do it.

 

[Turnerea]

It's best to set the aperture between f/16 and f/22. The shutter speed doesn't matter. Just make sure to lighten the image up properly. You will need a tripod.

The OP had asked about not letting the stars move... so as i read it- NOT star trails, but points of light- shutter speed will definietly matter. Certainly anything over 20 seconds will show movement of the stars. A lot will depend on the conditions of the sky- how much light from a nearby city there is etc, but I'd say you need to stay under 20 for sure if you're looking for the stars to be single points.

That or purchase a drive that will move your camera as the earth rotates

 

[BrandonS]

Search the net. Depending on what lens you use is going to determine how long you can leave your shutter open before you get apparent trails. You could make a mount like suggested. They are called Scoth Mounts. Just search it and you'll come up with sites to make it and there are a few different variations.

I've looked into doing this myself, but haven't had the time. In any case you have a D90 which is good on noise control. What I would try is going outside with your nifty fifty, stop it down for sharpness to maybe 2.8 or so, stick your shutter speed at maybe 15-20 seconds, bump your ISO up to about 800 or so and see what you get. Adjust accordingly for any blur or horrible noise you may see.

Also look up stacking images. I can't find a site that says how to do it (and I really want to know), but you can get a program or use a graphics program to stack the images (a bunch of shorter exposure shots) together to produce accumulatively what a long exposure on a moving mount would. One of the good things about this is noise is random in each shot and the stars are not. So once you aligned all the layers based on the stars (because they'll move) the noise can be removed based off that point of luminance or what have you not appearing in each image. It's a way to get a nice black background.

That's all I've figured out so far from research. If anyone knows the answers to any of this please feel free to add it for the OP's sake and mine.

 

[iflynething]

Also look up stacking images. I can't find a site that says how to do it (and I really want to know), but you can get a program or use a graphics program to stack the images (a bunch of shorter exposure shots) together to produce accumulatively what a long exposure on a moving mount would.

I have been unable to successfully do this. I can't figure out how to merge 5-10 pictures of 5 min exposure each and just have the different star trails visible.

~Michael~

 

[BrandonS]

I have been unable to successfully do this. I can't figure out how to merge 5-10 pictures of 5 min exposure each and just have the different star trails visible.

~Michael~

If you are just going for star trails you should be able to make each picture it's own layer in photoshop. You won't have to align anything if you use a tripod since they'll be framed the same (barring any movement from pushing the shutter button). I'm not sure what blending mode you'd use, but whichever one adds brigthness from the last would be it I would imagine. Or you could just use layer masks.

 

[iflynething]

I'm not that familiar with layer masks. What exactly would I mask? The landscape...the sky?

~Michael~

 

[astrostu]

So much information here ... some good ... some not so good ...

Stars-no-trails means relatively short exposures. I've done the math before, and in fact I've posted a guide here on how to do the math to figure out how long of an exposure you need to get the trails to be a certain number of pixels ... just work backwards to get that number to around 3 or 4 (about as big as the star will likely be). Sear in the Articles of Interest section to find my astrophotography series where I discuss the star trails.

From a more practical standpoint, about 20 seconds with a 35 mm lens (on a 1.6x sensor) as the longest I could do without getting visible trails. The relatively short exposures means you want the lens as wide open as possible (while stopped down a little to maintain sharpness). You may also need to do what I always recommend against, and that's bump up the ISO.

Stacking images does not need to be done manually. There are free programs for both Windows and for Mac, plus Photoshop since CS3 can do this automatically. For Windows, there's a program that nearly everyone uses but for some reason I can't think of it and a simple google search didn't come up with it (sorry!). For Mac, there's Keith's Image Stacker, which will also work on Windows. For pay, there's AutoPano Pro which I love for panoramas, but I've not used for stacking. In Photoshop, there's loading files into a stack and telling it to automatically align everything for you (in the File menu under something like "Automate").