Simple Astrophotography (Part Three)

In the last two days we’ve discussed simple ways that you can use basic photography equipment that you very well may already have sitting around to take simple but decent photos of astronomical events. What else can we do?

The next simple step for me, which is still really a work in progress since my results are pretty spotty to date, is video. I’ve got a decent, palm-sized, HD camcorder. What can it record?

Turns out – not much, at least not yet. The first problem is that digital video is basically just a whole bunch of 1/30 second exposures recorded and then played back rapidly in sequence. As we saw with the moon & comet photos on Monday (2.5 second exposures) and Tuesday (15 and 30 second exposures), when you’re taking video of things that are dark (i.e., some variant on the twilight or night sky) you need a long exposure to gather enough photons to show anything. 1/30 of a second isn’t going to cut it.

I also said to try it to see what happens, fail early, fail fast, fail often, learn from it, adjust, fail again, and so on. Which I’ve done, trying several times to record the International Space Station as it flies overhead. Video lends itself to an ISS overflight since the ISS tends to be bright (as bright or brighter than Venus or Jupiter) and fast (crosses the sky from horizon to horizon in just five minutes or so).

First of all, if you haven’t seen an ISS overflight, do so ASAP when the opportunity is available. It’s stunning, especially when you realize that it’s a spaceship that’s the size of a football field weighing almost a million pounds with crews continuously occupying it for over twelve and a half years. When the timing is right for it to be passing over your location just after sunset or just before sunrise, you can easily see it soaring across the sky, a sight both beautiful and inspiring. There are apps that can tell you when it’s visible from your location for the iPhone, Android, or your computer. Trust me, it’s great! (I will admit to preferring the evening passes just after sunset over the early morning passes just before sunrise.)

On April 8, 2013 at 19:11 PDT there was an utterly fantastic pass over Los Angeles. Sometimes a pass will be off to one side of your location and you’ll only be able to see the ISS for a short time and it won’t get very high above the horizon. The really great passes are the ones where the ISS comes right overhead and you see it from horizon to horizon. There had been several pretty good passes over Southern California in the evening in early April, but the April 8th pass was supposed to be the best of all. I again tried to get some good video.

I mentioned that the first problem with video is the short exposure time of each frame. The second problem I’ve found is that to really see the ISS well you need to zoom in, but once you’ve done that you lose all reference points so you don’t really see that the ISS is moving. As you track it across the sky you just see it as a bright dot on a dark background. (You will NOT see the ISS in detail with this simple setup. See here and here for some fantastic pictures done by some amazing photographers with some big equipment – Thierry Legault’s entire site can be browsed for hours!)

The third problem is that it’s very difficult with the typical handheld, commercial, household, consumer camcorder to see what you’re recording when your subject is really dark. In the old days (like, ten years ago) you had the option of looking through a lens and seeing the image you were recording, much like you do with a DSLR still camera. These days, unless you’re using professional quality video gear, you’re looking at a flip out LCD video screen a couple inches across. That flip out screen does a lousy job of showing a dark image, which your recorder is doing a lousy job of recording to being with, so in large part you’re just blindly pointing the camera in the general direction of your target and hoping for the best. You’ll find out later if you “caught” anything.

So it was on April 8th as the ISS rose in the west-southwest and headed for the zenith. It was so bright that I was able to actually see it on the flip out monitor most of the time and I shot a video that’s about nine minutes long as I was waiting for it to rise, spotted it, moved the tripod a couple of times as I maneuvered around trees to keep the ISS in view, and finally watched it disappear to the northeast. Since I had no clue if I was actually capturing on video any of what I was seeing, I kept a running commentary going so that I could at least use the audio from the recording to know what was going on.

Once back inside, from that nine minutes of raw footage, there’s one twenty-six second segment that I think is pretty cool. One of the reasons that it’s cool is that by sheer luck I dodged problem #2, the lack of reference for the ISS’s motion. The ISS’s path that night took it right up through the constellation Orion, and even with the video’s problem with short frame exposures, the bright stars in Orion can be (barely) seen. Here’s an annotated frame-grab from the video, showing the three “belt” stars of Orion, the “left leg” star (Saiph), the location of the “sword” of Orion, and the ISS. (I’m pretty sure I can see the sword stars faintly in the original, “m2ts” format, 46 MB, uncompressed video — perhaps not so much in the converted, compressed, “mp4” format, 4 MB file uploaded here. Let me know if you can see them when you view the video.)

Remember that yesterday I mentioned “noise” and “saturation” on video chips when recording something really dark, effects which give a grainy, colored look to the image. The chips in DSLR’s are bad when you get to 30-second exposures. The chips in HD camcorders are a lot worse, looking ratty even with these 1/30 second exposures. The stars are a little easier to see in the video than in this screen captured image (thanks to the “persistence of vision” effect, I’m guessing), but to make it a little easier to follow along, here’s what you’ll see and hear in the video after the credits end.

0:10  “Zooming back out” [Zoom out to see some trees in the twilight, you can also see Sirius, a really bright star, on the left side way up above the tree there — at this point the ISS is perhaps 30 degrees above the horizon]

0:13 “Zooming back in a little bit” [ISS visible in center of frame, Orion’s “right foot” star Rigel, a bright one, visible at lower right — after a second or two, quickly pan up to follow the ISS and then hold the camera position on the view shown above]

0:18 “OK, let’s watch it go across the field.” [ISS goes up right past the “belt”, passing through the frame in about fourteen seconds]

0:32 “That is gorgeous, it is going to come right up overhead” [Pan up again to follow ISS, “belt” stars disappear off the bottom of the frame]

Lights (reflected sunlight off of the ISS’s solar panels will do!), Camera (a Canon Vixia HF R100), Action (4.791 miles per second)!

It’s not fantastic – but I think after a bunch of failed attempts it’s a great first positive result. And I’ve got some ideas for what to try next. (For one, I’ll use my “professional radio voice” to narrate instead of my normal “whiny nasal voice”, on the off chance that the video might be successful.)

As always, your comments and critiques are welcome!