10 things to know about Astro-photography
What camera equipment do you need for star photography?
You will need a tripod, a dSlr camera and a wide lens.
Good gear does help to get great results.
Important to understanding is that stars will start to show movement in the sky if you leave the shutter open for too long. In order to calculate this maximum distance you can use the 500 rule
The 500 rule
The 500 rule for shutter settings says divide 500 by the focal length of your lens to get a star setting which is long enough to let in the light but short enough not to show the trails that are captured as the earth turns in its orbit . So for a 14-24 mm lens set at 14 it will be 500/14 = 35. For a 20mm lens it will 500/20 be 25 seconds and so on. Remember if you are using a crop lens camera you will need to multiply the camera focal length by 1.4 or 1.5 depending upon your make of camera
The Galactic Centre and timing your shot
The most prominent part of the Milky Way, called the Galactic Centre and is usually at a great angle and not too high in the sky in the winter months in the southern hemisphere. Plan your shoot for the new moon when there is least ambient light and head to a place such as the Karoo where you can be assured of clear skies and very little ambient light.
Using an app like Photopills or the Photographer’s Ephemeris you can predict the exact location of the sunset and the moonrise and also the position of the milky way and also where the sun will rise or set. It will also help you find a strong foreground and plan any special lighting effects you might plan.
What sort of shot are you after
Generally there are 3 different approaches to star photography. Lets call them standard milky way shots, star circles and time lapse. The first is the creation of an image that shows the stars as pin pricks. This is the kind that I like most — as its the most realistic — and luckily its also the most straightforward to accomplish with an exposure time that is as short as possible. As explained above I have a wide 14mm lens and using a setting of 30 seconds at 2000 ISO I am going to get a pin sharp image at the correct exposure. Or that is what I hope! There are still quite a few issues to consider before getting the shot.
First you need to line up your shot and in the dark it’s not that easy to achieve. So generally I will do my setup during daylight hours and then be ready to fire off the shot, or sequence of shots, using the in camera timer or manually. If you end up doing the setup after dark it’s useful using a flashlight or focus at 100% in live view. The point just short of infinity usually gives pin sharp stars and a sharp foreground. Once I have set my focus I often tape the focus ring so it does not shift.
There are plenty of ways to add creativity to this sort of image. The most common technique is to create a strong foreground. We often use boabab trees, windmills or rocky outcrops but anything will do as long as its graphic and forms an outline against the night sky. Building on this technique you can decide to do a composite image to give foreground detail (often shooting the first shot in daylight will allow this) or you can even do some light painting with a torch. Light painting is lots of fun and you will be surprised just how little light you need to illuminate things in darkness and at such high ISO settings. Often just a second or two of painting will do the trick. Or use a really dumbed down light source.
The images can be combined in photoshop or stacking software.
Star trails
If you want to get star trails you can lower your ISO right down to 100 and then shoot images of anything from 2 to 20 minutes or longer. Of course you will get noise on these long exposures and so the best way to get star trails is to shoot a bunch of images and then combine them in star stacking software. Do remember to turn off noise reduction between the shots or you will get gaps between the trails as the camera records the second NR image.
It’s easy to create a dramatic time lapse movie which will track the movement of the stars which can then be turned into a dramatic movie with sound. The most popular video making app is called Premier Pro from Adobe but download Da Vinci Resolve a free app which is really terrific. All you need to do is copy the images onto your timeline and it will create the movie for you. When creating time lapse stills you need to set your camera to intervals and then shoot images of a time period of some hours. A movie will play at around 25 frames per second so if you need a 30 second video you are looking at 750 images which need to be combined.
Star circles
If you want to create star circles you need to focus on the southern most point in the sky. This can be calculated using your photo app or by using the old technique which is by using the Southern Cross. Draw an imaginary line from the top of the cross to the bottom and extend it 4,5 times. Drop a vertical point from here to the South Celestial pole which is due south. As mentioned If you want stars to appear as sharp, individual points, your shutter speed needs to be faster than 500 divided by your lens focal length. Stars start to blur over longer periods. 20 minutes will give good star trails, but a single 20 minute image can be noisy. Rather, stack multiple exposures together. Use manual settings to get a good exposure at 30 sec. Continuously take 30 sec exposures for 20 minutes or longer using remote release and camera set to continuous drive mode. You will get 40 to several hundred photos to stack in software such as star stax.
If you want to find some terrific places to stay to practice your star photography contact David Rogers on the contact form.
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