Thoughts on astro photography for time lapse

[Ron Hunter]

I am interested in getting time lapse video of stars as they move across the sky, and this has caused me to experiment with camera settings in pursuit of "what looks good" for a star image. In case others have thought about this but never tried, I wanted to share some thoughts that might get you started.

Basic equipment and settings include:
- Canon Rebel T4i with 18mm-135mm IS STM lens set to 18mm.
- Battery grip installed with 2 batteries. My most recent attempt at an astro timelapse failed because my single battery died after 3hrs. The battery grip with 2x batteries should change that.
- Camera mounted on tripod.
- Manual exposure mode, shutter set to "Bulb" and aperture set wide open (f/3.5 on this lens).
- Manual focus, single shot mode.
- Intervalometer used to vary the exposure time (how long the shutter stays open).

Here's some of what I've learned so far:
- Dark sky is best if you can find it.
- Moon-less nights are your friend. The moon adds so much light it makes it hard to get a "dark sky".
- Try to avoid parts of the sky that have airplane traffic because the moving aircraft will create visible tracks in your photos.
- Avoid long exposures (>20 sec) if you can because star movement will be apparent in the image, and this will cause the stars to look fuzzy instead of sharp.
- For my setup, ISO400 and ISO800 work well. ISO1600 causes the images to look like the sun is about to rise, and this is somewhat offputting for a "sky image". Anything higher than ISO1600 is worthless.
- Good images can be had with exposures between 5sec and 15sec. Longer exposure = more stars but familiar constellations become hard to discern when more stars are present. 5sec looks more "real", like if you just stepped outside and can see some stars but not a huge amount (until you adjust your eyes to the light). However, if you want lots of stars to be present you will need an exposure longer than 5sec.
- Reciprocity! When you double the time the shutter stays open (e.g. 5sec to 10sec) you double the light used to make the image. When you double or halve the light used to record an image, you have went "up one stop" or "down one stop". ISO works the same way; ISO400 to ISO800 is a "one-stop" change. Therefore:...an image taken with 20sec and ISO200 looks like an image at 10sec ISO400 = 5sec ISO800 = 2.5sec ISO1600. The shorter the exposure time you want to use, the higher the ISO you will need, and vice versa.
- How long to wait between exposures for a time lapse? Websites suggest 15-60sec interval between images. I used 30sec interval and the resulting motion in the timelapse (24fps) was VERY fluid. I probably could stretch that out to 60sec with no problem. (Since the battery died half-way into the session I only got enough photos for a 17sec timelapse, which is why I haven't posted it here.)

Long story short, ISO800 @ 10sec with a 30sec interval is a great starting point. This creates an image that is dark enough (won't look like a sunrise), has plenty of stars, and still allows constellations to be visible. And the 10sec exposure time does not have any "star movement" to make the stars look fuzzy. Not bright enough or not enough stars? Try 15sec. Not dark enough? Try 5sec.

Try this out and post up what you get! I'll try to upload that 17sec timelapse to Vimeo...

[Ron Hunter]

My first astro timelapse (17sec of glory!) can be found here:


I included a portion of my house in the frame to use as a reference for the motion. You may notice that the house lights up occasionally, this is because my son cut on the porch light when he took Joey out. D'oh! And I also aimed the camera at a portion of the sky that includes aircraft making their final descent into Charlotte's airport, thus the tracks in the images.

Hopefully I can create a longer timelapse now that I have that second battery!

[momoffduty]

Thanks Ron for putting things in an easy to read info. Very clear time lapse too! That wasn't on my list, but I think you have successfully side tracked me.

[Dave McElderry]

Although I don't have any plans to try this, it's very interesting anyway. It's great that you took the time to put it all down for anyone who might want to try it out. It's one thing to know that the Earth is spinning, but it's always cool to see this happen in time lapse. Thanks Ron!

[_Paz_]

That's cool, Ron. I have an old 10" reflector that had a motor timed to move with Earth's rotation. I wonder if it still works? Never used it to photograph stars or galaxies. Just look at them. Globular clusters and Jupiter's moons were my favorites. Well, Saturn's rings are cool too.

Old telescope. Very old. In fact, it hasn't been out of the shed in decades. Weighs too much. More than me. Although it is possible to break it down into segments to move it.

When we first moved here we had dark skies. Then each of the neighbors decided they needed 2 to half a dozen street lamps in their yards. Sort of messed things up.

We moved here on the day the Shoemaker-Levy comet hit Jupiter. Bone tired, we didn't set up. Then the next day there was all the hoopla about being able to see the crash and the new spot it created. rats

Um, on a happier note, that's cool, Ron!!

[BuddyB]

Very nice. I like it much!