How To Shoot and Process a Star Trail

Light trails left by the stars after a 30 minute exposure.

Star trails, like the image above, are fairly easy to do.  You'll need some equipment to capture the images and Photoshop CS to blend the images.  You'll also need a dark sky with an unobstructed view.  The view in the image above is to the northeast.

You'll need:  Camera with a bulb setting, sturdy tripod, programmable shutter release like the Canon TC-80N3, fully charged battery, storage card with lots of room.

Set the programmable shutter release to take an unlimited number of photos at a 4 minute exposure with a 1 second break in-between exposures.  (Suggestion: Do this inside in the light because it's darn hard to read the instruction book in the dark when you're trying to shoot.)

Outside under a dark sky, put the camera on the tripod and point it at the sky.  Hook up the programmable shutter release.  Compose the photo to include some foreground or an interesting subject in the foreground.  Point the camera at the north star for a star spiral. 

Set the camera to Bulb, f/3.5 or f/4.0, ISO 400, jpg format. 

Take a couple of test shots to get the stars in focus.  Then turn off your auto focus.  (Suggestion: take these images are a really high ISO so the exposure is quicker.  Enlarge these photos on the LCD panel to check focus. Delete them when ready to start shooting.)

Reset the ISO to 400.  Make sure the camera is locked down on the tripod.  Press the "Start" button on the programmable cable release.  Monitor the first couple of shots to make sure the shutter stays open for 4 minutes, closes, and then reopens.  Let the camera keep shooting for at least 30 minutes but hours are better.

When finished, take the last image with the lens cap on.  This is called your dark image. 

To process the images, follow these instructions precisely to create a layer blend in Photoshop. 

(1) Download the images into a folder.

(2) Open Photoshop Bridge and then open the folder.

(3) Highlight all the images.

(4) Click Tools>Photoshop>Load Files into Photoshop Layers. Photoshop should open with the images in a layer pallet. 

(5) Move the “painted” image to the top of the stack if it is not already there. 

(6) Move the dark image so it is under the painted image.  (If you have a dark image. When doing a star trail, the last image is dark.  I take the last image with lens cap on to create a dark image.)  No dark image.  Don’t worry.  Keep going.

(7) Click the first image in the stack and change the blend mode to Lighten. 

(8) Right click that layer and click Copy Layer Style.

(9) Select all the other layers except the dark photo and the bottom photo. 

(10) Right click the layer and select Paste Layer Style. 

(11) Click the dark layer and change the blend mode to Difference.  The last layer should still be in the Normal mode.

(12)  Flatten the image to see your photo of the star trails. Make any necessary exposure, contrast or other corrections.

Enjoy!!