Long exposure shots at night?

[mrfinster]

Any tips on doing these?

Presumably darker is better for getting the stars streaking on the sky, so I need to wait for no moon?

How long can I leave the shutter open at ISO100/F22 before the shot turns to crap?

I'm living in the country, no street lights etc, and got a cracking view of the mountains and night sky, so it's something I'm keen to have a go at.

[gjanz]

Moonlight is good, it can paint you some foreground. Don't put the moon itself in your shot.

Use your in camera NR, it takes a 2nd exposure with the shutter closed to get heat/light spill from in the camera (and hot pixels) and removes that from the original image.

Otherwise take your own black image and do it manually later in photoshop, if you're taking quite a few at the same time length.

As rjd mentioned there's a program to stack shorter (30s to 5m, etc) into one shot to get a full swirl. I think things get odd with really long exposures - heat issues on the chip.

[Lance v]

Any tips on doing these?

Presumably darker is better for getting the stars streaking on the sky, so I need to wait for no moon?

How long can I leave the shutter open at ISO100/F22 before the shot turns to crap?

I'm living in the country, no street lights etc, and got a cracking view of the mountains and night sky, so it's something I'm keen to have a go at.

Have you got a remote that you can set a shutter time for?

Also theres no exact rule for how long you want to leave it open for.

You can try taking a shot at say f/4 at ISO 16000 and see how long the exposure time is.

Then you shoot at ISO 100 and at say f/16 which is 8 stops difference

so you take the time you got at ISO 16000@f/4 and double it 8 times.

So if it was 20 seconds you would double it
1=40s
2=80s
3=160s
4=320s
5=640s
6=1280s
7=2560s
8=5120s

If that makes sence to you. as you can c a 85 min photo you need a programable remote lol

[Ashley Daws]

I've not tried a stary sky long exposure yet. The only long exposures I've done at night are single grabs of the ocean.

From what I've read you need to do multiple short(ish) exposures say at f16 ISO400 for 30sec and them blend them in PS or whatever.

I haven't watched this fully but......

[ame="http://www.youtube.com/watch?v=OmZSBu_rtFY"]YouTube - Night Photography: Stacking Technique For Star Trails - TMELive.com[/ame]

[SteveB]

I spend a bit of time pointing my camera skywards, although I haven't done too many star trails.
It depends a bit on what you want. With digital, you're better off to use multiple exposures and then stack them to get long trails rather than trying to get a single shot.
Do some test exposures to find your limiting factor. I have to get 50km out of Auckland before light pollution isn't the limiting factor. For you, it will most likely be dark noise from the camera. Turn off the in camera NR and take a series of shots at different ISO and shutter speeds with the lens cap on in a dim room. Just look at the jpegs to find when you start seeing noise and limit your exposure to a bit below that. Stacking will get rid of a lot of noise. You don't want the NR on for your trails as it will give you gaps and you'll end up with curved Morse code.
Easiest technique would be to set the camera on 30sec, pick an ISO that is dark at 30sec (from above), set your aperture to your foreground isn't over exposed on a single shot (under exposed is OK because to can add stacked images). Put the camera on repeat and lock the shutter with a standard cable release.
If you want round star trails with the centre in your shot, point it south. The centre point is about 40 degrees above the horizon. If you want curves and no centre point, aim north. If you want straighter ones, east or west. However, if you are going for the straighter ones, you're better off to aim either side of east or west because the trails one one side curve to the south and on the other, curve to the north. You end up with an odd looking picture. You may need to arrange your mountains to suit.
Shots at the pole take longer to get nice looking trails than those near the equator.
That's all I can think of for now. Ask away.

Steve.

[duncan]

You may need to arrange your mountains to suit.

seriously, this lot of info sounds very useful, thanks!

[rjd]

SteveB - ace info - will give that a try tonight passing Tekapo.

[gjanz]

You don't want the NR on for your trails as it will give you gaps and you'll end up with curved Morse code.

Depends on your camera and length of exposure. 4m exposure on my older d70 gave me purple blooming, which in-camera NR would remove.

The better alternative is if you know you're taking a series of photos the same length, afterwards, put the lens cap on, set to f22+, and take a blank frame. Then use a tool to subtract that photo from the rest.

[Azza]

Wow. This stacking business sounds pretty tekko.

I had a crack at star trails a while ago. This is a 240 second exposure at ISO400 taken in my backyard a few months back.

[AnthonyKo]

A lot of useful info here, I'll share mine.

I did a test shot few month ago in Nelson, which was still a very busy city at night, but luckily there was a mountain to cover the most of lights from city. What I done was first using high iso to see the correct exposure time, like f5 ISO12800 60sec will be ok, then stay at F5 but only use ISO200 to lower the noise. Thus you need to increase the time of exposure too, from 12800 to 200 will be 6 times decreasing (12800, 6400, 3200 etc.. ), so 60sec times 6 = 360sec...

So that's what I did, and I don't even know it's right or wrong theory
And since then I have no chance to do that kind of shot again...

[rob]

Here is my two cents worth. Not sure if you have to go to such a high F-stop. Moon is fun. It's just out of the frame on the upper right.
D90
10mm on Sigma 10-20
F4
-0.7 EV (oops got to remember to to zero that for night stuff!)
ISO200
30 seconds