A small guide on how to take and process astrophotography pictures, with a tripod

Hello everyone

Let me introduce you to a photographic subject that I'm particularly fond of : Astronomy photography or commonly called Astrophotography. I will explain the steps you need to achieve to get some great shots of the sky.

First, I'll speak about gear, and what you need to get :

• A digital camera, even a point-and-shoot will do ( but a DSLR is better )
  
• A fast good image quality lens, manual or autofocus ( maximal aperture of f/2.8 or better )
  
• A sturdy tripod ( one that doesn't move or flex in mild wind conditions )

And that's it. You don't really need a cable release since you can use the camera timer ( I use a two seconds delay, but that depends on the sturdiness of the tripod and the focal length used ). And I won't speak about pictures shot with telescopes, equatorial mounts, tracking devices since it's quite complex.

Now, I got a small "check list" that I do before each session :

• Set the camera to the highest usable ISO setting ( 3200 for the 5DmkII, more on that later on )
  
• Set your mirror to "lock up" ( cancels any vibrations due to mirror slapping )
  
• Set your Custom White Balance to a value around 3100-3600 K ( you'll thank me later )
  
• Set your lens to "manual focus" and focus with Live View at x10 on a bright object ( star or light ) at infinity
  
• Set your image quality to the highest RAW ( CR2, NEF, etc )
  
• Check the weather outside, haha.

Like daylight photography, astrophotography have rules. As you may know, stellars objects ( stars, planets, comets, etc ) don't move at the same pace as Earth does. Here a list of what that implies :

• The longer your exposure time, the more likely you'll notice "trailing" ( drifting stars )
  
• The longer your focal length, same as above for a given exposure time, and vice versa

So your goal is to find a balance between exposure time, focal length, ISO setting and noise. Each model of digital camera got their noise threshold ( acceptable noise results ) : the 5DmkII is 3200, the 50D is 800 ( 1600 sometimes for short exposures ), etc. You have to experiment with those first hand and see what works for your setup ( don't forget that reducing your image size will reduce noise as well ).

To set your maximum acceptable exposure time ( the less trailing possible ), just shoot and see if it's very noticable or not on your LCD screen at x10. The shorter your focal length, the longer you'll be able to set your exposure time. For example, on a full frame camera, you'll be able to have an exposure of 30 seconds at 14mm, 8 seconds at 85mm, etc.

Next step is to find a reasonably dark site. People living in crowded cities will have a hard time finding one, so just check the internet and Google "XXX light pollution map" where XXX is the country you live in. Weather websites are handy too, especially if you have to drive several hours to get to your dark site ( arriving and seeing clouds, or even rain isn't funny at all, trust me ).

So now, you have everything set to be able to capture sky pictures.

Once you have all your raw shots, it's time to process them, and that can be pretty time consuming, espcially if you like nip-picking like me, haha.

You'll find here a raw file from something I shot some time ago, this way you'll be able to see what it looks like before being tweaked with Photoshop and Lightroom.

Then I open the file in Lightroom and only apply "Lens corrections", to cancel the vignetting and correct the field ( important especially if you merge several images together ), and I right click on the image and "Edit it in Photoshop CS5".

I apply auto tone, contrast and color ( sometimes not all of them, just one or two of those auto features, depending on the result )

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You can see that the colors are a lot better now, but there are all those purple/magenta fringing due to chromatic abberation. Luckily for us, Photoshop has a great tool to remove that : selective color correction ( it works for daylight pictures as well, most of the time ). Select the magenta color from the drop down menu and adjust the "Magenta" slider to about -75%, Cyan to +50%, Yellow to +100% and Black to +100% as well and you should get this :

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A lot better, isn't it ? Now duplicate this layer and set the opacity of the top layer to 60-90% ( depends on the picture, choose 70% for this one ), then adjust the "Curves" of the bottom layer to boost the luminance/brightness to get this :

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Adjust the "Contrast" of the top layer to 50-70% ( 60% for this image ) :

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Adjust "Vibrance" then "Curves" on top layer to get a high contrast result :

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Resize your image to a better size ( 1920x1280 is good for the web ), "Smart Sharpen" on the top layer to about 30%, 1 pixel, "remove lens blur", flatten the image and you should have this result :

IMAGE LINK: http://www.flickr.com …6/sizes/o/in/ph​otostream/

Those are the major steps I follow, but I often add a little tweaking here and there, and fiddle with the sliders and values to reach what I consider a more pleasing feeling when viewing the image. The best way is to experiment and practice, honing your skills and forming your picture signature, your own take at your image.

I hope you'll find this little guide helpfull, and if you have questions, don't hesitate to ask me right here

You can also check my Flickr and take a look at my Milky Way pictures, most of them ( 99% ) are done using this guide : a DSLR, a lens and a tripod.

@ Jimmy and Chris : Thank you guys

@ Lerroy : I did say that I use the "2 seconds timer" and you don't really need a remote The reason why I advise to set the WB at around 3100-3600k is because it'll give you a better color rendition of the stars while using auto tone, contrast and/or color. Most of the time, people ( and myself included when I started doing this kind of pictures ) obtain a reddish overall hue, which isn't very accurate.

Here are two exemples of what I'm speaking of :

IMAGE LINK: http://www.flickr.com …/in/set-72157623131239346
Auto White Balance

IMAGE LINK: http://www.flickr.com …231386986/in/ph​otostream/
Custom White Balance ( 3500 )

Of course you can change this after shooting the picture since you use RAW files, but that's one less step to adress in Post processing And sometime Photoshop "Auto" feature goes wild if you change the WB on the RAW. I hope that helps you understand why I said that

Oh, and Lerroy, I see that you got a Samyang 14 f/2.8 : it's a wonderfull lens to capture the sky Here an autoportrait I did some time ago using it :

IMAGE LINK: http://www.flickr.com …7554876572/in/p​hotostream

Custom white balance too, set at 3400. You can see that the palm trees are green, the yellow tint coming from the city lights.

Interesting, for whatever reason I've always shot in RAW and set mine at Daylight (5000k), which if no/little light pollution blacks looked black, but light pollution showed up a slight brown in sky.
I've used in CS5 Noels tools to remove light pollution.

Of course shooting in RAW WB does not really matter, as you can easily change WB in post processing.

Here is one of my images @ WB 5000k (this is RAW>TIFF during stacking):

Same one just the WB to 3400K in TIFF file:

I'm on the fencepost here which one I like "better", both have their qualities.

The brown tone sky seems to add some "warmth" to the image, while the blacker/darker sky does make the star trails pop more......

Thx for posting this, give me one more post PP item to consider for image presentation.