Digital Night Photography: Test Exposures, Noise Reduction, and Image Stacking

A tree, trailer, fencing, and various geometric forms studied for 15 minutes -- by Joe Reifer

A tree, trailer, fencing, and various geometric forms studied for 15 minutes — by Joe Reifer

Technical Details
Canon 5D Mark II with an Olympus Zuiko 21mm f/3.5 lens — the lens is very small, light, sharp, and has a manual focus scale.
Long exposure noise reduction was turned off in the camera, greatly increasing productivity and battery life.

The test exposure to check the composition and histogram was 15 seconds at f/5.6, ISO 1600.
Let’s do the math: moving to f/8 is 1 stop, to f/11 is 2 stops, to ISO 800 is 3 stops, to ISO 400 is 4 stops, to ISO 200 is 5 stops.
We compensate for closing down the aperture and reducing the ISO by changing the exposure length 5 stops: 30 seconds is 1 stop, 1 minute is 2 stops, 2 minutes is 3 stops, 4 minutes is 4 stops, 8 minutes is 5 stops.
The result: 8 minutes at f/11, ISO 200.
Because the main subject is white and metallic, I protected the highlights by slightly reducing the exposure to: 7.5 minutes at f/11, ISO 160.

To achieve the 15 minute star trails in the image above, I set the Canon TC-80N3 Timer Remote to make 2 exposures in a row of 7.5 minutes at f/11, ISO 160.
I adjusted the RAW files for tone and color in Lightroom.
With both files selected in Lightroom, go to the top menu and select: Photo — Edit In — Open As Layers In Photoshop.
Next just set the top Layer to Lighten Blending Mode as pictured below to add the star trails together. Lighten Blending Mode adds anything on the top layer that’s brighter to the bottom layer – when you flip to Lighten Mode, voilà – you’ve added the star trails together.

Lighten Blending Mode in Photoshop to Stack Star Trails -- by Joe Reifer

Lighten Blending Mode in Photoshop to Stack Star Trails — by Joe Reifer

Remember: The secret to making this technique work is keeping the interval between exposures to 1 second or less. Otherwise you’ll have unsightly gaps in your star trails. I hope this useful technique saves you time and battery drain. Give it a try the next time you’re shooting at night.

5 thoughts on “Digital Night Photography: Test Exposures, Noise Reduction, and Image Stacking”

  1. I learned this technique from you a long time ago and I’ve shot some great photos with it. Thanks again for taking the time to share this technique. It’s really fun! And as for the TC-80N3 remove, its a lifesaver for night photography!

    1. Hey Basim – The question of when to use in-camera noise reduction comes up pretty often, so I thought I’d revisit this technique. Glad you found it useful!

      1. I rarely, if ever, use ICNR (mostly due to decrease of productivity and battery life). Even with ICNR enabled, there’s still issues of not getting bright enough star trails and sensor bloom. With shorter exposures that are intended to be stacked, I can open up the aperture more to get the shorter burn-in and still be exposed properly and the star trails are nice and bright. This technique I learned from you is my favorite!

  2. Hey Joe-

    For those shooting with a camera that has an ISO setting of 6400, doing the math on high ISO test shots couldn’t be easier. 1 second at 6400=1 minute at ISO 100 for any aperture, so correspondingly, 10 seconds = 10 minutes, 3 seconds = 3 minutes, etc.

    For Nikon shooters with a native 200 ISO, 1 second at 6400= 1 minute at 200 -1 stop on the aperture.

    It’s great not to have to worry about equations and exposure equivalents in the field…

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