Time lapse night sky image

[choochoo_baloo]

Dear all,

I want to experiment taking time lapse images of the night sky from where I live, but with a slight twist. I wish to have the buildings which are are a key part of the composition along the bottom, with the rest of the frame filled by sky. I wish to capture the stars' arc trails. 

I have a Nikon DSLR, and tripod, and remote shutter control. I have fiddled with the 'bulb' setting before but never properly looked into it. But my main concern is how to I ensure the correct 'detail/contrast' of the foreground buildings, with their fairly sporadic artificial light, do not blow away all the precious photons gathered of the arcing stars over say a 45 minute exposure? It seems a fairly popular method of long exposure sky imaging. The image I found on Google portrays exactly what I hope to do (similar composition of the buildings and their light intensity):

I'm guessing it must be fairly simple to keep out the excess artificial light whilst slowly collecting that of the stars?

Many thanks in advance.

[jambouk]

Here's a guide i recently put together:

http://www.eastmidlandsstargazers.org.uk/topic/6922-star-trail-guide/?fromsearch=1

I look forward to seeing what you achieve.

James

[TractionMan]

Here's a guide i recently put together:

http://www.eastmidlandsstargazers.org.uk/topic/6922-star-trail-guide/?fromsearch=1

I look forward to seeing what you achieve.

James

That's a very nice and well written guide.

[choochoo_baloo]

Yes thank you James, very good. Will let you know how it goes. What role does stacking play then?

[Langy]

I've had thoughts about doing something similar, but I want a detailed star sky to be over buildings of some type.

So my photographic background says to me to capture the sky first with as much detail as possible, somewhere with a very dark sky. Then I will take the images of the buildings separately and use PhotoShop to bring the two together.

I'm not sure of your situation for where the buildings are, but it will be safer and quicker to capture them that way especially as the sky image in your case is going to take a lot of timed exposures. Capturing the buildings can just be experimental with a few short exposures.

[jambouk]

Stacking puts all the images on top of one another. In the old days of film, you'd leave the shutter open for an hour, two hours, six hours, and have all the trails on just one exposure.

Now, what I do is to take lots of much shorter exposures (but leave the camera pointing in the same place all night), and the software stacks all the short exposures to make one effective long exposure.

Doing one long exposure is still possible, but I find there is too much sky glow / light pollution / hot pixels / movements of the camera / over exposure in general.... Especially if you have something which is giving off light or reflecting it in the foreground you'd want to keep individual exposures to a minimum.

It is very much trial and error. I think stacking images where various lights from a sky scraper have gone on/off would be fine, but I like stuff in the foreground.

JD

[Russe]

Very interesting idea - waiting in anticipation for your great results!!