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Hey there! I'm Dave Hearn and I'm the Director of Kissimmee Park Observatory. In this Star
Hopping "Extra", we're going to start a new Feature Topic; something many of you have
been asking about: Basic Astrophotography, and the 3 ways you can start to capture the
Cosmos with your camera. More about all this great stuff right after this - stay tuned.
Hey Hello Hi and welcome to Episode 22 of Star Hopping with Kissimmee Park Observatory!
I'm Dave Hearn, and I'm absolutely elated to be your host. In this series of programs
we'll show you the most beautiful sights in the night sky, and explain exactly how to
find them with your binoculars or telescope.
So this is going to be the first episode to cover a brand new Topic area on Star Hopping
- Astrophotography: capturing the night sky with your camera. I have received some requests
from a few of you out there to start some basic discussions about the process, procedures,
and equipment needed to capture beautiful astronomical images with your camera.
One of the main challenges with visual astronomy, especially with beginners, is that deep sky
objects generally appear very different in the eyepiece of the telescope as they do in
the pictures they have seen that initially attracted them to the hobby; in the telescope,
most objects appear ghostly white and without color. That’s because the sensory cells
in our eyes just are not excited enough by the dim levels of light coming from these
objects through the eyepiece. Not to say that the photons are dull and boring, it’s just
that they are dim!
But everything changes when you use a camera and start taking time exposures: setting your
camera to open its shutter for much longer than usual, as compared to when you take terrestrial
photos or normal snapshots. These pale deep sky objects then appear in vivid colors like
reds, pinks, greens, and blues, and are sublime to behold. When you capture your first successful
astrophoto and see that color, it is absolutely amazing and you will definitely be hooked.
As you may know, when shooting a regular daytime picture, the camera shutter opens for a very
short period of time, say 1/2000 of a second. When that shutter is open, it “exposes”
the CCD sensor in the digital camera to light - this is known as an exposure. When you do
astrophotography, in order to collect enough light to form a sufficient digital image in
the camera, exposure times are measured in minutes and sometimes hours.
The biggest challenge to this concept is that while that shutter is open and the camera
is collecting light from an object in the sky, the Earth continues to turn, and the
celestial target moves in the sky on a line from East to West. Unless you have some way
to counteract that motion, you will end up with trailed or blurred images; and clearly
(or unclearly in this case) that’s just not what you want.
So your options are to counteract that motion, or to avoid the motion altogether.
So, how do we do it? Here are the three basic methods for taking an astrophoto, going from
the most simple to the most complex. They are:
Time Exposures of the night sky using a fixed tripod, which lets you create star trails
or time lapse movies. Mounting your camera on a mount or telescope
that is tracking the stars, otherwise know as “Piggybacking”, which lets you take
images of large deep sky objects, like this. Mounting your camera on the focus of a telescope,
thereby using the telescope as a long telephoto lens. This allows you to capture smaller objects,
and get closeup images of deep sky objects, like this.
Now astrophotography is an extremely complex topic, and there are many variations of processes
and procedures for each of these, so I definitely have plenty of content to cover for this new
Feature Topic! If I tried to cover all of these even at a high level in one episode,
we’d be here for a couple hours, so we’ll cover just Method #1 in this episode and get
the rest over time.
So before we get too far, let’s talk a little about the camera. I came up in astrophotography
using SLR film cameras. SLR stands for “Single Lens Reflex”, meaning there is a single
detachable lens on the camera and the optical view from the lens was reflected by an angled
mirror inside the camera. The light then bounced to a prism than reflected the view from the
lens to a viewfinder that you could look through with your eye.
In today’s world, we have “DSLRs”: Digital Single Lens Reflex cameras. This is primarily
what I know about, so that’s what I will be presenting in this series. It’s amazing
what some people are doing with the cameras in smart phones nowadays, and also GoPros,
and there are tons of tutorials out there for that. So we’ll be talking about using
Canon DSLRs for astrophotography, which is a very common selection of many astrophotographers
of all experience levels. There are other more advanced options like CCD cameras, that
I can discuss in future episodes.
In these episodes I’ll assume you generally know the features and functions of your camera.
I’ll explain important terms and settings that are needed to accomplish a specific type
of astrophoto, but again, for learning basic DSLR camera usage, there are zillions of tutorials
around the internet.
So with all that said, onward and upward! Let’s talk about time exposures using a
fixed tripod. There are lots of cool opportunities for great images here. One of the easiest
is a polar star trail, like this one I took of comet Hyakutake at the pole - they can
be quite spectacular. This is an instance where you actually want to show the star motion,
and it’s the whole point of the image. In the northern hemisphere, all the stars appear
to rotate around the North Star Polaris in the constellation of Ursa Minor. It’s important
to find a location where you will have a dark sky to the north. Light pollution will definitely
ruin this kind of shot.
So for this type of image, you’ll need the following equipment (and I’ll provide links
to some of them in the episode notes): A DSLR camera with the exposure time set for
30 seconds. Make sure your battery is fully charged, and have a spare as well, as long
shutter durations tend to suck up batteries. A fairly wide angle lens, 50mm or less. The
wider the better really, for this kind of shot.
A sturdy tripod An electronic cable release, an intervalometer,
or a computer that sets up a repeating set of timed shots.
These kind of shots are more interesting if you have something on the ground in the shot;
a line of trees, or a building, or some other interesting foreground object. Place your
camera on the tripod and frame up the shot - make sure you have the ground and sky well
above Polaris in the frame. Open up the aperture on your lens the whole way to pick up the
most stars. On your camera set the ISO setting to 1600. The higher you set the sensitivity,
the noisier the images will be - 1600 is a nice middle ground that will let you get lots
of stars but a reasonably low noise level.
Take a series of timed exposures and try to minimize the time between shots. Keep at this
for as long as you can - a couple hours of exposures give you a nice long star trail.
At a 30 second exposure you’re looking at 120 frames per hour! That’s why it is nice
to have an intervalometer or computer to automate the whole procedure. But it can be done by
hand if you bring coffee.
So after you are done with this sequence you will have many successive frames you will
need to combine, by “stacking” the images on your computer. There are lots of pieces
of software that do this - I use “Nebulosity” by Craig Stark, and can do a demo on it sometime
in the future. When you stack all the images you’ll have a complete arc of stars around
Polaris.
A second type of image sequence is a tripod shot pointed at another area of sky, like
the Milky Way or generally any nice dark area of sky with an interesting starscape. The
procedure is similar: take many exposures of 30 seconds (or less depending on light
pollution). Then you can take the sequence and ensemble them into a movie using software.
On the Mac, I use Time Lapse Assembler, which is free. This results in a neat time lapse
that shows the stars slowly moving across the sky.
There are some units out there that control the whole imaging process, and between each
image, is slightly rotates the camera, so in the end there is a slow pan that really
enhances the time lapse. I have a unit by Alpine Labs called “Radian”, that will
automate a series like this and perform panning functions too, as you see in this movie - I
can do a review of the product in a later episode - it’s really great.
The speed of the motion in the movie is dictated by the frames per second that you select when
you assemble it. 15 frames per second is about the minimum you can use to get smooth motion.
24 or 30 frames per second will give better results. So if you take an hour of 30 second
shots, you’ll end up with 120 frames to work with. Then at 30 frames per second, your
time lapse movie will only be 4 seconds long! At 15 frames per second it will be 8 seconds
long. So again, the more frames you take, the longer your movie can last.
If you don’t want to make a movie, and only want to capture a single frame, then you can
set your camera exposure to “Bulb”, use an electronic cable release as I mentioned
earlier, and then experiment with exposure length to get the most stars, the least light
pollution, and the least star trailing. The wider the lens, the longer your exposures
can be before the stars begin to trail. This is a way I mentioned at the start of this
episode to avoid the star motion. You can also play with your ISO setting on the camera
to increase sensitivity, and then use shorter exposures to avoid the trailing. Just remember,
the higher the ISO, the noisier the images. The name of the game here is experimentation
- with patience you can get some great shots, like this one taken in the field at KPO.
So we’ve entered a fantastically exciting and complex area of astronomy in our study
of basic astrophotography. We started out discussing the three basic forms of astrophotography,
which are: Time Exposures using a fixed tripod, Piggybacking your camera on a mount or telescope,
and Mounting your camera on the focus of a telescope.
Then we dove into Fixed Tripod astrophotography and talked about creating star trails around
the pole, and then explained how to create cool time lapse movies showing stars moving
across the sky over time. Lastly we talked about capturing single image wide star fields,
by experimenting with exposure length and ISO settings.
Over the next months I will inject one or two episodes between the normal Star Hopping
episodes. It will work out well, because we do occasionally have to wait for more interesting
targets to rise in the east between Star Hopping episodes.
So that does it for this week’s show. You can find the show notes on our website at
kpobservatory.org/SH022, where you can comment and leave any questions that you may have.
Thanks for joining us, and I’ll see you next week in our episode of Star Hopping.
I’m Cassie, and I hope you've enjoyed star hopping around the Milky Way. We'll continue
to bring you these video astronomy tutorials every week on Thursday, and in their podcast
format on Fridays. They will be designed to help you find deep sky objects that are up
in the sky at the time we post them on the Internet.
The reason we create these video and podcasts is to help beginning amateur astronomers learn
the sky and get more enjoyment out of their telescopes and astronomy in general. If you
have any requests or suggestions of potential targets in the night sky that you would like
to see us present, just let us know down in the comment section below, or on our website
blog.
Don’t miss our free Field Notes for this episode, basically the script of the show,
with all the images and start charts we use for our star hopping activities. You can get
them for free at kpobservatory.org/FieldNotes.
If this is the first time you’re checking out Star Hopping, and if you found this video
useful, please consider Subscribing to our Channel by clicking the Big Yellow Button
down there, click the Thumbs Up on the video, and please share this tutorial out to your
friends who like looking at stars. Also, as I just mentioned, please feel free to leave
any question or comment below, and we will be sure to respond quickly.
Also, please follow KPO on Facebook, where we post all of our astrophotos and keep everyone
informed about upcoming astronomical events. We'd love to hear from you to discuss all
this great stuff up in the sky.
All the links to these places including our website kpobservatory.org, can be found below
in the Episode Notes as well.
And finally, if you feel this video provides you value, and if you'd like to see more,
please consider supporting us on Patreon, where for a small amount per video, you can
support our efforts and let us make even more great astronomy tutorials like this one.
Well thanks again for watching, and we'll see you next time on Star Hopping with Kissimmee
Park Observatory.