Astro Tutorial

What goes into a great astro photo?


Astrophotography isn't easy. It takes time, a lot of practice, knowing your gear, a lot of practice, a degree of planning, more practice, and a bit more practice! You just need to get out under the stars and see what happens ;)

I chose this image because it contains everything a good astro shot should, a good composition that leads your eye with good foreground interest, an epic mountain and lake scene and a well positioned Milky Way, and I also used a technique called focus stacking to keep everything across the scene in focus, so thought it would be good to touch on this :)

The first thing you need to do is plan your shot.

I knew from google maps that the view towards Mt Cook from Hooker Lake was facing north and eventually the Milky Way would line up behind Mt Cook around 8pm once it got dark (August 27th). You can use apps such as Photo Pills to plan your astro shoots, however I just go off memory and observation, and a little bit of guess work ;)

As for planning my composition, I knew I would have Mt Cook in the centre of the frame with the Milky Way coming out of it vertically, but I had no plans for the foreground and just went with whatever I could find, the patches of ice bergs lining the shore did quite nicely!

The settings I chose were my usual "go to" astro settings of;

Canon 6D with the Tamron 15-30 f/2.8

ISO10,000 - such a high ISO is very noisey but gives you a lot of light information to work with.

f/3.5 - This aperture is noticeably sharper than f/2.8 with less vignetting in the corners.

15mm - Wider is usually better with astro images as you generally want as much Milky Way as possible.

25 seconds - At 15mm, 30 seconds gives you a little bit of star trailing, 25 seconds reduces this nicely.

I shot 3 frames, one focused to infinity, one focused on the edge of the water and the last focused on the front of the ice in the foreground. Focusing in the dark is tricky, for the 1st shot I put my camera in live view mode and in manual focus, zoomed in on the brightest star I could find and played around with the focus ring until the star was as small as possible. For the next 2 shots I used my head torch to light up the foreground and zoomed in in live view to focus on each spot, choosing the edge of the lake, roughly 1.5 metres away from me and the ice which was about 0.75 metres away, spreading the depth of field evenly across the frame to make sure everything would be in focus once blended together.

Heres what the RAW files look like with each focus area circled;

I processed each file in Camera RAW, syncing each shot so they match when focus stacked;

I also clicked the "Remove Chromatic Aberration" box in the lens corrections tab and set the vignetting to +33, I usually don't use lens profile corrections, just a personal preference :)

once opened in photoshop, I copy/paste my 2 foreground focused shots on top of the background focused shot and add a layer mask to each layer, the layer mask button is circled;

Now the fun part, focus stacking...

When focusing on something closer to the camera, the movement of the glass in the lens has the effect of zooming in slightly, so the shots focused on the foreground need to be ever so slightly enlarged to fit perfectly with the background image. To do this i use the free transform tool (command "t"), hold shift and drag the corner until the image looks the same size, then reposition that layer until it lines up with the background. to check this I flick that layers visibility on & off while slightly adjusting to make sure they match up correctly. This can be very fiddly and take a bit of time, so be patient and don't rush cause it makes blending a lot easier! At 100%, you can see how little I enlarged this shot for it to match the background;

Once aligned, I used the gradient fill tool (command "g") to paint in each image into the areas of the foreground that were out of focus in the background shot, make sure you are clicked on the layer mask in the layers tab! You can also use the brush tool (Command "b") to paint in where needed, if you have objects in your foreground that vary in distance from the camera then you will need to selectively paint them in with the brush tool. To avoid blurry areas in your blend, use a small brush with a hard edge, or a very short gradient with the gradient tool so there is no mushy bits between images. I do all my blending at 100% zoom or closer to make sure things are perfect.

Now the whole image is in focus, we are ready to continue processing!

I start with using some luminosity mask adjustments (I use Tony Kuyper's free luminosity masks) with a curves adjustment for contrast, then a levels adjustment to bring back more colour in the brightest areas of the Milky Way. I grouped the Levels layer and added a second layer mask to paint in that adjustment in just the areas I wanted, so it does darken every star in the frame;

I then move on to using the Nik Color Efex Pro 4 software to add some filters. I play with the settings of each filter in Color Efex Pro and then layer mask in where needed. All of these adjustments are where your artistic eye really comes into play, have fun and experiment with them and see what you like!

Starting with Tonal Contrast, I fill the layer mask to 66% across the frame and paint in with the brush tool 100% over the foreground rocks and Milky Way.

Darken/lighten center I paint out around the foreground ice to keep it bright, slightly paint out of Mt COok so it isn't too bright and paint out of the darker areas of the mountains on either side to retain shadow detail.

Pro Contrast added some nice contrast and brightened up most of the image a little, i just painted it out of the foreground rocks and a bright part of the milky way slightly.

Sunlight is a very intense glowy filter and can ruin an image if not used sparingly, I used the fill tool to fill 15% across the frame, then painted in the effect slightly across the foreground ice and Milky Way with the brush tool at around 20%.

Classical soft focus is another glowy filter to be used sparingly, I dropped the layers opacity to 63%, filled the layer mask to 33% and then painted across the lake, foreground ice and sky with a brush at 33% (I like 33% haha)


I then did another quick luminosity mask adjustment using the bright lights levels, bringing down the brightness of the brightest parts of the milky way, again grouping the layer and adding a layer mask to paint in the adjustment where circled;

Lastly I do some sharpening and noise reduction.

to sharpen, i hit command, option, shift, e to create a new layer and use the smart sharpen filter at 77% and a radius of 0.8px, lowering the layers opacity to 55% so the effect isn't too intense, as sharpening a noisy image too much can look pretty ugly!

For noise reduction i use the amazing software, Nik Dfine. Its as easy as clicking on the Dfine button in the Nik software tab in photoshop and it automatically does its job. once loaded into photoshop i add a layer mask, fill the frame to 55% and paint in over the noisier areas in the foreground rocks and dark areas in the mountains on each side, while also painting out some areas around Mt Cook and the brighter parts of the Milky Way to retain a bit more sharpness and detail. the finished product;

I tried to keep this tutorial as short as possible, so any questions please don't hesitate to send me an email at;

or message me on my facebook page;


Thanks for reading!