Milky Way photography - how?

[The Stig]

Esteemed forumites,

I'm trying to get my head around photographing the milky way. As winter approaches here in Norway (well, technically it's still fall, but tempus fugit...) I can look forward to(?) short days and long and hopefully, clear nights. Needless to say I'm hoping to make the most of this period.

I've seen some pictures of the milky way that was taken with some pretty middle-of-the-line DSLR equipment, and I'd like to give it a shot myself. The only problem is that I'm helplessly confused and have no idea as to where to start. I want to shoot the milky way, and I've gathered that you need to stack exposures to do this. How do I do this? What kind of software do I need? Is said software something that will play nice with Lightroom 3, or do I need PS? If so, will Elements do?

I've also understood (from star photography mistakes I've already made) that the celestial bodies move quite a bit. I understand that there's some piece of kit that that will adjust the angle of the camera. My questions are obvious: What kind of hardware do i need, and is it expensive?

In closing I'd like to say that I obviosly have no idea how to go about this. Can anyone help shedding some light on this?

Thanks in advance,

Cheers,

Stig

[Nass]

In terms of astronomy hardware, unless you're at a very wide angle and short exposure, you need something called an "equatorial mount", which moves the camera to keep up with star rotation. Or the Pentax O-GPS1 which does the same thing by moving the sensor. (equatorial mount is same as star tracker).

[McQ]

I'm sure others will chime in on this as well, but in a nutshell:

For the entire milky way you'll need to use a wide angle lens, and without a star tracker (these can be expensive), you'll want an exposure time of no more than roughly 15 seconds (otherwise you'll get star trails, as you mentioned). That will mean you'll need to crank the ISO up to at least 3200 (or higher), and use a large aperture. The aperture choice is a little tricky though, because using lenses at their maximum aperture often yields "coma" distortion near the edges, and is much more likely to cause other aberrations. You'll need to find the right balance between (i) minimizing aberrations and (ii) maximizing light for your particular lens. This will likely require some experimentation.

For the best quality, you'll want to stack a series of these ~15 second exposures, but since each will be rotated, you'll need to align or "register" the images with pixel precision. Sometimes you can get this to work in photoshop (use Edit > Auto-Align Layers), but I've found that this doesn't work well at all for wide angle star shots at high ISO. Maybe you'll have better luck with that, but the only fail-proof alignment I've found is to do it manually using a panorama/stitching program and control points (I used PTAssembler). If you plan on taking a lot of these types of photos though, I'd really look into a star tracker (aka equatorial mount).

Here's an example milky way photo from a couple of weeks ago that's an average of 21 stacked photos. It was taken at the lens's widest aperture (f/4), so you'll notice some blue fringing around some of the central starts (not ideal). If I were to do it again, I would've used f/5.6+ and averaged more photos to compensate for the decrease in light (and resulting increase in noise).


Canon EOS 5D Mark II
Canon EF 17-40mm f/4L IS USM - 15s f/4.0 at 17.0mm iso6400 (averaged 21X)

[FrankMi]

Fascinating! Thank you for posting the technique, Sean!

[The Stig]

Thanks for a clear and easily understandable answer. Follow-up question: I've seen examples of these where you can see some landscape details as well - a tree, a small hill etc. How would one go about doing this. Am I right in guessing a star tracker would be of no help here? For example the one called "Blazing Bristlecone" (sorry, no link) - which I'm sure many of you know.

Stig

[McQ]

Yes, a star tracker would blur the landscape. The vast majority of the time when lots of non-streaking stars are visible and landscape detail is present, the image was a composite of two or more exposures. Sometimes the land is dark enough that it won't get burnt out, but even then one often runs into white balance issues. If you want to try and achieve this with one exposure though, use a wide aperture and high ISO, and then in post-processing you might need to brighten the land a little using a graduated neutral density (GND) filter effect.

[Dizzy]

A little bit about "star trackers"..

These are commonly known as "German Equatorial Mounts", or "GEM" mounts, and many just call
them "EQ mounts". Basically, these mounts will track the star or object in it's right ascension. Technically,
the Earth is what is rotating, not the star, and these mounts will keep you locked on that location as the
Earth rotates around it.

These mounts can be quite expensive, especially when you are mounting your camera on top of your telescope or tracking scope. Orion (also sold as SkyWatcher in other countries) has recently come out with an affordable, lightweight EQ-1 mount made for cameras only.

http://www.telescope.com/Mounts-Trip...34/p/27154.uts

I have not heard any reviews on it's performance, but a new user should be able to learn how to
set it up for accurate tracking with minimal effort. It must be "Polar Aligned", so that it will properly
track, and that takes just a few minutes once you know where Polaris (North Star) is located. In the
Southern Hemisphere Polaris is not visible, so they have a different method of polar alignment, and
it can be read about on Astroholic.Com or other astronomy sites.

A quick alignment (aligning to Polaris by eyeballing) should be accurate enough to allow for 3-5 min.
exposures with no star trailing. Longer exposures and you would want to do a very careful
alignment, meaning using a mount with a "Polar Axis Scope" built-in. That level of accuracy requires
time to set-up, and is generally left to those with their mounts on permanent piers.

The Orion mount above is very affordable, but it is very lightweight and can only handle your
camera and lens. I would not suggest this mount to anyone for even small telescopes, as it will take
far to long to settle-down after each touch of the scope.

Here is the mount I'll be using:



That is an Orion Sirius mount, fully motorized drives that are computer controlled, but without
the "Go-To" functions. It has 1-3/4" tubular steel legs, and weighs in at 43 pounds. A solid mount like this one runs about $1000 US, but it can handle up to 30 pounds of scope, camera and guide scope. I've modified a dovetail plate to hold my D90 and 70mm-300mm lens, and am looking forward to imaging some celestial targets over the next few months when/if the skies clear.

Mike

[Steaphany]

Stig,

Software, this will be at the ungodly price of FREE !

There are two great packages that are specifically designed for astronomical stacking:

DeepSkyStacker

RegiStax

I have both, use both, and find my images tend to do better with SeepSkyStacker, plus DeepSkyStacker has also come in useful for stacking terrestrial images.

And you'll need to learn a whole new world of terminology for image files knows as darks, flats, offsets and many more terms.It's not hard, just a bit different from what Photoshop users would be familiar.

[The Stig]

Thanks to all who replied. It seems I'll have to consider the different options - the lightweight cheap tracker seems tempting.

-S

[Steaphany]

Stig,

You do not need a tracker at all !

Just use a good wide angle lens with a fixed tripod. Aim your camera to the sky and set you shutter to something like 5 to 10 seconds. ( Nice and short to capture point source stars )

DeepSkyStacker and RegiStax both will compensate for the image to image drift of the stars, aligning everything to properly match, and stack the image. The edge of such a stack will be irregular needing a bit of a crop and you're done !

[The Stig]

Thanks Steaphany. Sadly for us Mac users both programs are Windows only

Stig

[Sahil]

Another 'Very-easy-to-Understand' tutorial by Sean.
Thanks Stig & Sean.

[Wendy Stanford]

Thanks to all above for such an interesting thread, waiting for clear skies to go out and experiment

[Steaphany]

Sadly for us Mac users both programs are Windows only

Then please take a look at this site:

Macintosh Computers in Amateur Astronomy

The list isn't just image processing packages and I have no experience with anything listed there. ( This was just one link from the 1.2 Million that a quick google returned. )

[The Stig]

Wow

Thanks, I'll take some time and look through the different options - or maybe I'll limit myself to just the first 600!

[dthomp]

Is there a program out there (or Android app) that you guys know of that tells you when the milky way is visible relative to where you are? I'm finding a heck of a time finding one... or something like it. This would be most helpful as it seems that sometimes it isn't viewable until very late at night and other times it seems to be viewable very early.

Any thoughts on how to track that?

Thanks!

Dan

[Dizzy]

Is there a program out there (or Android app) that you guys know of that tells you when the milky way is visible relative to where you are? I'm finding a heck of a time finding one... or something like it. This would be most helpful as it seems that sometimes it isn't viewable until very late at night and other times it seems to be viewable very early. Any thoughts on how to track that?
Thanks! Dan

Hi Dan,

The Milky Way is always there, however city lights (light pollution) and weather play a huge role in your being able to see it. The Milky Way that we see is the outer arm of our galaxy, as our solar system sits about 2/3 of the way out from center of the Milky Way Galaxy. In the US you can currently find the "bottom end" of it in the South, and the "upper end" in the North, with everything else in between. Your best bet to see it is wait for good sky conditions (cloudless and dry air) and go to a location with very dark skies, away from the city.

Mike

[dthomp]

Right... but as the earth turns, it effectively moves across the sky. So what I'm looking for is something that says, if you're standing at this location, then at 12AM it will appear on the eastern horizon, at 2AM it will be in the center of the sky... etc, etc. So if you're wanting to take a picture of it over a certain object (mountain range, whatever) you'll know what time you need to be there without just showing up with your lawn chair and waiting. All this, of course, dependant on the conditions you've mentioned.

Thanks!

Dan

[dthomp]

As an example of something I just stumbled upon (scroll to the very bottom):

http://homepage.mac.com/rarendt/Galaxy/youcansee.html

Dan

[Steaphany]

Dan,

Sounds like you are looking for http://www.stellarium.org/