Stellar Time Lapse

As you may have seen in an earlier post, I had made an Arduino-based remote intervalometer for my EOS camera, with the intention of making a time-lapse of stars and hopefully the Milky Way rotating over the Pacific Ocean. I had gotten the inspiration for it when reviewing some exposure bracketing I had done when making some still images. When quickly reviewing the images it looked almost like a movie, so I adjusted the brightness and contrast of the images, and strung them together as a video proof of concept:

Over the holidays I got a chance to try it for real. There were a few changes I wanted to make to the intervalomenter to prepare. To implement these changes I needed to add a rotary encoder with a push-button. The initial design enables changing of intervalometer settings while it was running, but that would have required three interrupts, and the Arduino Nano has only two. So instead, I tied the push-button to one of the interrupts and used it cycle through four states. The interrupt routine still needs some debouncing, as it's currently pretty easy to accidentally skip a state.

Here are the states:

1) Run:

Periodically trigger a shutter release while displaying the mode and time to trigger on the LED display.

2) Change operational mode:

A: Interval in seconds and immediate shutter release.

B: Interval in seconds and delayed shutter release.

C: Interval in minutes and immediate shutter release.

D: Interval in minutes and delayed shutter release.

3) Adjust the interval from 1 to 99 seconds or minutes.

4) Adjust the duty cycle of the display from full-on to full-off in increments of 10%.

All of these worked fine, except for the fourth. I thought this feature would be helpful because the display was so bright and got so warm, I was concerned that it would drain the intervalometer battery before the camera battery was drained. It turned out that the display was just as warm with the LEDs disabled.  Since this feature didn't do what I had intended, I ended up just unplugging the power from the display, once the intervalometer was started.

I found that an interval of 30 seconds would look pretty good. And, with a 10 second exposure and the 15 seconds it takes for the camera to process the image, it's quite possible. However, I found that when doing time exposures, the camera's battery lasts only between 150 and 180 images, and that makes a video that's only five or six seconds long, covering only 90 minutes of real time at most. So until I can set up an external power supply for the camera, I've set the interval to 60 seconds and made the video with 2 frames for each image, or 15 rather than 30 frames per second.

I used the following camera settings:

    Sensor/Lens combination: Crop/12mm
    Aperture: f2.8
    Exposure: 10 Seconds
    ISO: 12800
    Image Size: S2 1920 x 1280
    Display: Min brightness to save energy.
    Long Exposure Noise Reduction: Enabled

I made the video in Kdenlive by selecting "Project", "Import Slide Show Clip", importing the still images, then setting "Frame Duration" to "00:00:00,2".

It turned out pretty well, especially the way it shows Venus and Jupiter setting on the Pacific. One thing that bothered me, and you'll probably notice it now that I mention it, is that occasionally the image jerks. I wondered if there could be some missing images, so I wrote this script to calculate the intervals between all the images. And, sure enough, occasionally the interval was 120 or 180 seconds rather than 60 seconds.

Perhaps using an infrared shutter release wasn't the best idea. Maybe a wired shutter release would be more reliable. I also checked the Arduino specs and it turns out that the the digital pins can only source 20 mA. I should have driven the LED with a transistor that would have provided more current.

One happy coincidence occurred on the night of my first test run. The night of January 1st was the first night in almost two weeks that the sky hadn't been completely obscured by rain clouds. I didn't notice anything unusual in the sky until I had assembled the still images into a video. Was that a comet in the first second of the video? Yes! Here's a still from that sequence. Just go straight up from the palm tree. It's comet Leonard which, according to NASA, will never be seen again because if it survives its closest approach to the Sun, it will continue on a trajectory out of the solar system.