One of my
favorite side-activities when at a star party or even out at the observatory by
myself is timelapse. You can create
videos of the Milky Way rising behind an observatory, activity on the observing
field at the star party, your telescope tracking across the sky, planes zipping
through the night, clouds appearing and disappearing, a thunderstorm rolling through
– all kinds of things. Timelapse is also
my go-to for cloudy nights at the observatory so I can at least get something
for my drive out there! It’s also rather
easy to do with a DSLR and a tripod.
This method is also great for imaging meteor showers - you have a much higher chance of catching a meteor if you're imaging continuously, and then you get to make a neat video at the end too. Two for one deal!
This method is also great for imaging meteor showers - you have a much higher chance of catching a meteor if you're imaging continuously, and then you get to make a neat video at the end too. Two for one deal!
Compose Your Shot
Figure out
what you want in your foreground and your background. Clouds are more interesting to watch than an
empty blue daylight sky; the Milky Way rising is always pretty neat, or some
other constellation; telescopes moving or people moving around the observing
field also make great timelapses. I did
one at the Green Bank Star Quest of me and my minion Miqaela taking down our
gear at the end of the weekend with clouds rolling around in the sky at the
massive 300-ft telescope moving around (watch it here). I
did another one at the Texas Star Party of the Milky Way rising behind the
upper observing field, which was stuffed to the gills with people and
telescopes (check that out here). I’ve also done several of my
telescope tracking across the sky and changing targets. Daytime timelapse is fun too – clouds rolling
over hills, thunderstorms, weather fronts, traffic, people, all kinds of
stuff. Again, you are only limited by
your imagination!
Focusing
Focusing in daytime is easy - use auto-focus, and then switch it to manual focus during the timelapse sequence (and don't touch the focuser. At night, however, it's a little trickier, since your auto-focus won't work. See Part 10 of this series for a section on focusing at night.
Taking Images
Take several
test photos to decide on your ISO, shutter speed, and focal ratio. If you are imaging during sunset or twilight,
you may want to start out bright so that your images don’t get too dark too
quickly. Once you have decided, run your
camera in manual mode, turn off everything auto, including D-lighting, set your
white balance on something other than auto, and set your focus to manual. My intervalometer only goes up to 399, and my
camera’s interval timer goes up to 999.
Depending on your shutter speed, this may or may not be enough. During the day, when I’m using short
exposures, 399 will only get me 16 seconds of video at 24 fps, and any
interruptions in your sequence, like restarting your interval timer, will show
up as a jump in your final video. 999
frames will get me 41 seconds at 24 fps, and I’ve found that spending 30
seconds to a minute on a given scene in a video seems to be a good length of
time. For longer timelapses, I’ll
usually use digiCamControl on my tablet to take an arbitrary number of photos
(usually I’ll set it for like 3 hours and then just stop it when I need
to). For long exposures at night, it
depends on how long your exposure is.
The longest I can do without getting star trails is about 15 seconds at
18mm of focal length, but with timelapse, you can get away with 30 seconds,
since the images will be blurred together anyway. However, the longer your exposure time, the
fewer images you’ll be getting, so your final video will be shorter. I imaged the Milky Way rising over the upper
observing field at the Texas Star Party for about an hour and a half, and I
only got 180 images, which is only 18 seconds at 10 fps. But, I had a nice bright Milky Way.
Also, you
can go ahead and take these in JPG instead of raw.
Problems You Might Run Into
Battery life
is probably the number one inhibitor of timelapse. My stock Nikon batteries only last about two
hours in my D3100 that has a non-closing screen, and about four hours in my D5300 that has a closing screen. I’ll plug into AC power when I
can, but this limits where I can image.
So what I usually end up doing is when my battery dies, I’ll move to a
different spot and take another timelapse, since I don’t like jumpy gaps in my
timelapse videos.
Dew is also an
issue, at least at night. In the case of
humid nights, I’ll station my camera near my telescope, and run my 2-inch dew
heater strap over to the camera (I got an extension cord, but it’s a little too
long, so it’s very lossy, which means I have to crank the current up quite a
bit), and wrap it around the lens. I have a dew heater controller from Thousand
Oaks that can run four heater straps – one for my 11-inch, one for my guide
scope, and one for my timelapse camera.
I can’t use a blow dryer on it because you will see it in your
timelapse. I can’t even check for dew
because that will show up too. So the
dew heater is a good solution.
Another
option that astrophotographer Brent Maynard told me about at the Green Bank
Star Quest that I think is very clever is to use those chemical foot warmers
you can get at the grocery store or the gas station. The foot warmers are sticky on one side so
they’ll attach to your socks – they’ll also attach to the side of your lens! He even uses them on his reflector, spacing
them out around the ring, and using a stretchy band or extra tape to hold them
on. They work great. I've also used hand warmers attached to the lens with rubber bands - you only need one since they get quite hot. Cheap and simple solution!
Creating the Video
I mentioned
the app VirtualDub in my post about planetary astrophotography as a way to
convert .MOVs or .AVIs to a format of AVI that RegiStax likes. You can also use it to make videos and
animated GIFs. There is a little
pre-processing you’ll need to do to your images first, though.
First, get
all of your images in time-order. Nikon does this annoying thing where it rolls
over after 999 images, and then starts numbering again, from 001. This means that when you put them all
together in the same folder, you’ll have your first 001, and then 001 (1) from
when it rolls over, and then 001 (2) when it rolls over again…so basically
putting them in name order does not put them in time order. You can do this by going to the View tab in
the folder, choosing Details, and then clicking on the “Date modified” column
twice so that it’s in ascending order.
Windows, unfortunately, is very slow at re-ordering large numbers of
files, so be patient.
Once they
are in time-order, click on the first image, and then hit Ctrl + A for Select
All. Then, either press your F2 key, or right-click on the first image and
click “rename.” Rename it whatever you
want, and then hit Enter. This will name
all of the photos the same thing, but with a (1), (2), etc after it. This is necessary for VirtualDub to be able
to pull them all in to make a video. The
numbers have to be sequential – if
there is a gap, VirtualDub will only pull in images up to the gap, and then
stop. The first image has to be
(1). So if you delete some photos from
the sequence later, you will need to repeat this step to re-number all the
photos. Again, Windows is slow at this,
so give it a few seconds, especially if you have over 500 or so images.
Open
VirtualDub, and click File -> Open Video File, and then go to the folder
where your images are saved. Make sure
the “Files of Type” box says either “All types” or “Image sequence.” Click
on only the first photo in the list, which should be your (1) photo. Click Open. This will load in all of the
sequentially-numbered images in that folder.
Next, go to
Video -> Frame Rate. Here you have
some flexibility – 24 fps is about what the minimum is for motion to appear
smooth for the human eye, although I’ve found as low as 10 fps looks pretty
nice too, at least for timelapse. You can certainly go faster, but it depends
on how fast the things in your images are moving, and how long you want a
particular sequence to last for when the video is all compiled. Click the “Change frame rate to” radio
button, and enter what fps you want. Click OK.
Next, go to
Video -> Filters. Click the “Add…”
button. Now, your DSLR takes some pretty
large frames. Mine are 6000x4000, which
is greater than 4k video. HD video is
1920x1080. The larger your image frames
are, the larger your final video file will be – like, dozens of gigabytes. These take forever to upload to YouTube.
So, I reduce the frame size by clicking the “2:1 Reduction” filter, and
clicking OK. Later, I’ll compress it
further. Another option is to use a
batch resizing program beforehand to bring them down to a smaller size. I don’t use any of the other filters (besides MSU Deflicker - see below), although
you are welcome to give them a try (and let me know if you get any helpful or
cool results). Click OK.
Now, go to
File -> Save as AVI. Choose where you
want the video saved at, and then click OK.
A small window will appear showing progress. Uncheck the “Show input video” and “show
output video” boxes, which should make it run a little faster. Then sit and wait. Once it’s done, check out your video!
A word of
caution here. My homebuilt rig has a
NVIDIA GTX 1070 card in it, 16 GB of RAM, and an Intel i7 processor, and it
cannot play the giant video files that come out of VirtualDub smoothly. It’s glitchy and slow. So, your next order of business will be to
reduce the file size by compressing the video.
I use an app called Any Video Free Converter to do it. Simply drag the file in, set all of the video
and audio settings to “Original” or something reasonable, and then click
Convert. Even if you set everything to
Original, I think it changes it to a different AVI format or applies some other
compression algorithm, and the file size comes out like one tenth of what it
was – something like a few GB down to even hundreds of MB. Not only will this play on your computer
better, but it will upload to YouTube in an amount of time shorter than the age
of the Universe. I’ve found there not to
be much degradation in quality after the conversion process, particularly since
my computer screen is only 1920x1080.
Adding Audio
Your
timelapse video will be even more interesting with some flowy space music or
epic sci-fi anthems in the background. First,
figure out how long your video is going to be.
This is easy – just take the number of frames, and divide by the fps
you’re using – for instance, 1000 frames at 24 frames per second is a
41.7-second video. Second, find a song
you want to use. I’ve got a spacey
playlist I use at public outreach events that I draw from, and there is a lot
of that kind of music out there, especially for sci-fi video games. Then, I use the free software Audacity to cut
the song and have it fade out. Just import
the song, cut it at the length of your video, select about the last 5 seconds
of the song clip, and then to go Filters -> Fade Out. Then go to File -> Export to export the
song as mp3.
In
VirtualDub, with your image files still open, go to Audio -> Audio from
another file, and select your song clip.
I usually select the option of auto-detect bit rate, and it seems to
work well. Then do the same as before –
File -> Save as AVI to create your video. The audio will also be glitchy
until you compress the video.
Flickering
Sometimes,
your timelapse will see to flicker. This
is usually due to leaving some auto-setting on, like white balance or active
D-lighting. Don’t fret, your hard work
isn’t toast – there’s a great little plugin for VirtualDub called MSU DeFlicker. It does some averaging
between frames to virtually eliminate this effect. You can just take its default settings, or
play with it some if the flickering isn’t resolved with the defaults.
Conclusion
And there you have it! It takes a bit of legwork, but nothing too technically complicated, to make some kick-ass timelapse videos of the sky. Enjoy!
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