Lake Eaton star trails

How to make star trails

There are a couple of different ways to photograph the night sky with stars. If you shoot a reasonably short exposure then you get stars that are pin points. The exposures have to be fairly short because of the earth’s rotation. More than 30 seconds or so will start to draw the stars out into ‘trails’. You can get a longer exposure but you will have to mount the camera on some sort of drive that will rotate the camera in sync with the sky’s movement. You can make a mount to do this called the barn door mount out of a couple of boards, a hinge and a screw.

Google “barn door star photo”

and you will find many references and instructions for making one of these.

You can make stunning photos with that technique. Look at this one by John Moran

But our subject for this post is making star trails not avoiding them. To make the shot above I took 6 shots, each with 180 second exposures. And combine them using a technique called stacking.

A comment about that shot. I do not claim it is one of my best shots but it is the only successful star trail shot I have so far, so there it is. The red in the sky was from the urban lights from the City of Ocala about 15 or 20 miles away. The red comes from all the forest fires in the area, from the smoke not the flames which were 7 miles behind me. That area across the lake did catch on fire the next afternoon however, causing us to beat a quick retreat before they closed the highway out. Click on the shot for a larger version.

I could have made a single 18 minute exposure rather than 6–3 minute exposures. But the bane of night shooting is sensor noise and the longer the sensor is run the hotter it gets. By dividing the shot up into shorter intervals you can reduce the heating problem.

Now this shot was taken to the north but not quite far enough, the pole star is just off frame to the right. But getting a shot due north will give you concentric trails like this by Harold Davis. You can tell he has had a lot more practice than I have. Unless you live down near Key West or Brownville Texas in the US you won’t get the same effect by shooting south since the southern axis is below the horizon.

The stuttered dotted effect of the shot above was because I let a minute of so go by in between shots to demonstrate the effect of stacking. If you shoot them closer together you will get a continuous trail.

How I did the Stacking

I have Photoshop CS4 extended which includes stacking modes. Standard CS4 does not, CS3 extended does. The version Adobe sells as the educational/academic version is the extended version. So that being said I suspect that most of you will not be able to follow this method, but there are other ways. So I:

• Shot the images and loaded them into Adobe Bridge.
• In Bridge I compiled them into a stack by selecting them all and right clicking and selecting group as stack.
• You can then open tools–>photoshop–>open in photoshop layers
• Or you can download Russell Brown’s scripts which will add a Dr Brown’s Services menu item under tools and one of those services is Dr Brown’s Stack-o-matic. He seems to be having a problem with the scripts but they will show up on this page. He has CS3 and CS4 versions. He has a lot of good Photoshop material on that page too and the scripts do more than stacking. Select maximum mode from his script.
• Anyway, without Dr Brown’s help, go into CS4(or 3) and select all the layers then go to Edit->Auto blend  layers. You may need to auto align the layers first but do not unless you have to do so.
  
• Then Layers–>smart objects–> convert to smart objects
• Finally the Stack Modes menu item will be visible on the layers menu, select maximum mode there. There are a lot of modes and you can play with them.
• If you have a lot of layers in the stack be prepared for long waits as photoshop does the work.

You don’t have PS Extended.

In that case load the shots into layers in Photoshop as above then try to combine them using blend modes and opacity. Screen or lighten mode are likely to work the best and the opacities should probably be 30  percent or so. But you will have to experiment yourself or hit Google.

Other Stacking Software

There are a lot of non-photoshop ways of doing the stacking:

• Image Stacker (look at Max Lyon’s excellent panoramas when you are there)
• DeepSky Stacker
• Registax
• CombineZ

You are on you’re own with these since I haven’t used them. If you have a favorite let me know and I’ll add it to the list. I don’t know of any other photo editing software that does stacking but some may do so.

I’m probably going to step away from night shots for awhile and do some posts for new camera users.