8 October 2012

Tutorial: How to take photos of the stars - part 1

Note: this is part 1 of the tutorial. Click here to read part 2. You can also proceed to part 3 by clicking here.

Milky Way over Fuerteventura Island
So I'm finally writing what I promised a few days ago - a tutorial on taking photos of the starry skies. I won't describe professional astrophotography technique as we won't use telescope of any sort. I decided to break this tutorial into a few parts, today is the first one.

Photos of the starry sky typically fall into one of the two categories:
  • stars where the stars and the galaxy are sharp,
  • star trails where the the apparent motion of the stars is captured.
First part of this tutorial will deal with the first category, second part with the star trails and the last part with post-processing techniques and ideas.

Equipment

First of all I need to write a few words about necessary equipment. You will basically need 3 things:
  • fast wide-angle lens - the reason you will need wide angle lens is because the longer the focal range, the shorter the time in which the stars are points - i.e. don't become star trails. With a 50 mm lens (35 mm equivalent) you will have a maximum of around 30 - 40 seconds before the stars become blurry. Therefore the wider the lens, the more time you will have. Why the lens should be fast? I think that this one is quite obvious - the faster the lens the shorter time will be necessary to correctly expose the photo (so instead of 40 seconds you will be able to use 25 seconds for instance).
    Note that most of the time you will shoot wide open (more about this later) so it really makes a difference whether you use 16-35 f/2.8 lens or 17-40 f/4 lens. For all my recent astrophotos I used Canon 24 mm f/1.4 at f/1.4 which is one of the fastest wide-angle lens available on the market. As you may notice I was using exposures of 10 seconds. This means that when shooting at f/2.8 I would need to use 40 seconds exposures! So the lens makes a terrific difference. Please note that if you have f/3.5 or f/4 lens you can still take good photos but you will need to use longer exposures.
  • steady tripod - this one is obvious I guess. You will shoot long exposures so any shake due to the wind or shutter being released might ruin the photo.
  • remote release - same as above - this should be pretty clear. However, as described in one of my previous posts I don't use remote release at all recently. What I do instead is to use bulb feature of the Magic Lantern + 2 seconds delay.
One thing which might be obvious or not but will definitely help is a torchlight. It will make reaching the destination, setting up a tripod and a camera a lot easier and safer (there is nothing worse then falling to the ground with all equipment and breaking it).

Another useful accessory might be additional batteries. When you take long exposures and also it's quite cold (nights are usually much colder than days) the battery drains pretty quickly. So in order to have enough power for a whole shoot make sure you have more than one battery and that all of them are fully charged.

Choosing location

Stars above beach on Fuerteventura
Click on the photo to view it in large size on black background.


Before you start taking any shots it is very import you research the location during the day. Otherwise it will be very difficult to come up with a good shot in the darkness. Try to choose locations far from any cities and towns because their lights might make the stars less visible (and will also appear above the horizon but this sometimes might look quite interesting). All kinds of desert and mountain locations should work pretty well (unless there is a lot of particles in the air as they greatly decrease visibility).

Another thing you will have to avoid is moon. Although it's beautiful it makes stars fainter than they really are. So take your star photos when there is no moon or when there is new moon (avoid full moon at all cost).

One more thing which is good to avoid are clouds. Although sometimes they might make starry sky even more interesting, most of the time they will significantly decrease visibility of the stars.

Also make sure to start taking photos a few hours after sunset when it is completely dark.

Setting up

Before taking any photos:
  • disable Image Stabilization on your lens (or body)
  • switch to manual focusing
  • switch your camera to manual mode as you will definitely need to set exposure manually.
  • set aperture to the widest one (as you will most probably focus on the infinity so the depth of field will be huge) unless your lens is really blurry when it is wide-opened. If so stop it by 1 - 2 EV.
The most tricky thing is focusing. Basically you might consider focusing on the stars or on the object in the foreground. You can also take a number of photos and focus stack them later in Photoshop.

If you decide to focus on the stars you will need to set your focus to infinity. Word of warning here: to get sharp photos you don't want to set focus to the point where infinity symbol is drawn on your lens - it hardly ever matches infinity (most often it's a little before or after that point). If you use Canon DSLR you can use Magic Lantern which I already mentioned in this post. Set L.V. display gain to some high value (like +5 to +7 E.V.) and also set ISO to eg. 3200 (or more). Then switch to the Live View mode. Everything will be very noisy but you will be able to see stars somewhere between the noise dots. Zoom in and move focus ring until stars become points. If you don't want to use Magic Lantern or don't own Canon's camera take a few test shots until you will have ideal focus. Just a tip here - take your shots at highest ISO possible (even if there will be a lot of noise). This will make exposure times shorter and will therefore increase your efficiency.

I could write exactly the same regarding composing your photos. You either need to compose, take a test shot, recompose, etc. until you have desired framing or use Live View mode with Magic Lantern. The second one is definitely easier but it's up to you.

Taking photos

Colourful starry sky over Fuerteventura
I took several exposures to capture more detail and colour
and then merged the photos using blending modes
in Photoshop.
So you now have everything set up and you're ready to take a shot. So now let's say a few words about exposure. It greatly depends on the location and your aperture and ISO combination. Generally I start by setting ISO to some high value (like 1600 or 3200) and also exposure to something around 10 seconds. If the photo comes overexposed I decrease ISO by 1 or 2 stops (I prefer lower noise caused by the ISO). Most of the time it helps. But if the photo is still underexposed I make exposure longer (eg. 20 or 30 seconds). I try not to increase ISO above 3200 and ideally keep it in 800 - 1600 for acceptable noise levels. I also try not to go beyond 40 - 45 seconds exposures to freeze motion of the stars.

When the exposure is chosen you can start taking photos for real :) I usually take a few shots of the same frame (up to 10) as this have a lot of advantages. First of all you can then add the exposures in Photoshop using blending modes to create some cool effects (I will show this in part 3 of this tutorial) and you can also average the exposure to decrease noise!

Post-processing

Although I will write more about post-processing such photos in part 3 of this tutorial for now I will mention a few things you can do quickly to make your photos better:
  • Increase clarity and contrast in Adobe Camera RAW or Lightroom.
  • Decrease exposure of the foreground a little bit (eg. by 1/3 or 2/3 EV) to make stars stand out more. You can use gradual filter in Lightroom or ACR for this purpose (or use one when taking a photo).
Note: this was part 1 of the tutorial. Go to part 2 to continue reading. You can also proceed to part 3 by clicking here.

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