Long Exposure VS Stacking
The first technique is to do 1 single long exposure in BULB mode. In this picture below I left the shutter open for about 1 hour at F/5.6 ISO100. The only problem with doing star trails this way is that no matter how long your exposure is, it will take that same length of time to do the in camera noise reduction if using it. So this photo below took a total of 2 hours. I feel this method of star trail is more of an art form because it is like shooting film, so much effort goes in to one picture, then after all that time it could still come out wrong. It really teaches you about exposure, aperture and it's relation to light.
Now you have mastered standard exposures and star trails you can start adding light painting in to them as well.
So the image on the right is what our stacked image will look like, a lot of people make the mistake when stacking, of not doing a lighting shot, if you don't your star trail will look like this, a silhouette with a star trail. Now if there is any street lights or walking through the shot with the torch on you can use a black feathered paint brush to get rid of them, it may look messy but it will be ok once we blend the lighting shot in. Now we import this image and our lighting shot in to photoshop, your lighting shot will look a little something like the image on the left.You will have to paint out the static stars in the sky in the lighting shot to avoid getting the dot and line image I spoke about earlier. Once you have done this both images are ready for blending, drag them both on to the same file, so they are two individual layers, then you need to go in to the blending options, which can be found above the layers, it will say Normal at first but you need to switch to to Lighten, this then takes all of the lightened areas on the lighting shot and blends them in to the darker areas on the background shot. The end product will look like this.
Portaloo - 6, 5 Minute Exposures Stacked
This is now a mixture of single exposures and stacking, making a more natural trail but easier on your batteries and shutter life, the best of both worlds, but once again if you prefer one of the above methods or even if you have a different method do what is best for you.
Now if you are stacking, the long winded process of putting it together by hand would involve you dragging and dropping layer upon layer on top of one another and lightening each layer. So some great chaps have made some software to make the whole process easier, You download the software, install it on your Mac/PC and then click open, once opened you select the files you wish to stack, and click process, save and your done, if you don't like the final image, go back and tweak individual images then re-stack it. Simple as that, now the two main software packages are Star Trails which is a PC only programme, and StarStax which was first only available on Mac but is now available on all platforms.
Church - 30 minutes, 60, 30 second shots stacked
The only problem is some people tend to over edit their individual shots in stacked star trails to get thicker trails and it is a little too unrealistic looking, I leave my star trails compltly untouched apart from the blending process. A big draw back of stacking is the shutter life on your camera, every camera has a pre-determined shutter life, this is how many shots your camera can take before it realistcally needs replacing, the cheaper the camera the shorter the life, my first DSLR had a shutter life of 30,000 shots which I surpassed very quickly, I had minor problems involing the shutter button after this but it still carried on performing as I wanted it to. So if you are stacking 30 second shots, this will mount of very quickly so it is important to find out the shutter life before you buy a camera or before you start stacking. Each method has pros and cons but it is all personal preference on which one you prefer to use.
With stacking you will often have to do a lighting shot to bring out the foreground because of the shortened exposures, in the single exposure you would have had to do this within the star trail and if you make a mistake with your lighting you've ruined the entire shot.
The advantage of this method is you don't have to use in camera noise reduction and the stars seem to come out a lot brighter. Also if you do happen to fog up or frost over you can use the stack up until that point so the whole trail is not ruined. If there are any bad frames you can just edit out the bad bits from the star trail.
A third option is to do a mixture of single exposures and stacking, sounds weird I know but what I have started doing is, stacking 5/10 minute exposures, so I could do 3 10 minute exposures and stack them, they looks more like a single exposure but is actually stacked, it will also keep your shutter life in tact, you will need a timed shutter release unless you are planning on self timing the exposures which can be a pain.
Church Tower - 1 Hour Long Exposure
The problem with doing single exposures is that any light pollution near by will burn in quite badly and may cause the image to come out more yellow or orange, this will reflect in the sky as well as we can see in the image above. Also if the moon is out this will some what wash out the stars and they will appear fainter than they should be. I often face a problem at night called fogging up, this is where your lens steams up from a sudden temperature change or dew falling. Those with glasses will know how irritating this can be. In camera terms it will ruin you shot and more often than not your entire night, once your lens has fogged up it's not as simple as wiping it off, it is then out of action until it has returned to it's normal state, you will have to put it back in your bag and use another lens, if this is your only lens thats usually your night over. There are method I have tried to combat this but none are that effective. I used to cut up an old pair of socks and wrap them around my lens to try and keep it warm and stop the moisture getting to it, this was often topped off with re-usuable hand warmers stuffed inside the socks. There is a contraption for astronomers use to stop the same problem happening to telescopes, this can be quite pricey and does have to be powered which means more weight and bulk on to your equipment.
The second way to star trail is to do a series of short exposures with out in camera noise reduction and blending them to create 1 star trail. The exposures are usually 30 seconds long unless you have a timed shutter release, which makes it quite easy to work out how many shots you will use in a period of time. In a 30 minute stack you will use 60 shots.
The subject matter in a star trail is always important to me. It is much more rewarding than pointing your camera directly up at the stars and pressing go, this may be fine for your first star trail, but after a few images like this, they will all look the same. Finding the perfect subject to compose into your star trail will make the picture so much more interesting and eye catching. Taking the time to compose an interesting subject with the sky always pays off better.
There are two ways to achieve star trails and both work as well as each other, so it's all about personal preference.
You can always carry a compass for a guide, most phones have digital compasses now but I wouldn't rely on it as I often like to pin point the north star in a particular position in my image, often interacting with the foreground subject.
It is quite easy to spot in the sky as long as you know what it looks like. As we can see is consists of 7 stars. You will need to locate the big dipper because no matter what time of year it is it will be always be in the same relation with the north star. What you need to do once located the big dipper is follow the line on the bucket straight and the star directly in it's path is the north star as shown below.
How to find the North Star
People often struggle to find the north star because to most people they have never had to know before and wouldn't know where to start. A basic knowledge of Astronomy can see you through to get the shots you want. If you wish to further the knowledge you will start to learn about different things that may come in to your image, for example venus if often out near to the moon and can be visible in your images, also in your star trails you may find little shards of light reflecting of the international space station orbiting earth as well as the occasional shooting star. Lots of interesting things to be learnt along the way but i'll stick to the basics for now.
Firstly you need to find the Big Dipper (The Plough) which looks like this.
Finally the best I could do from my location, the stars slightly curving to the north at the very top of the image and to the south at the same time.
In This image we can see how the stars curve down towards the south pole, although the south star is not present we do get slight southern curvature in the northern hemisphere.
This image is below is how an equator star trail will look. Straight lines no curvature to north or south.
There are a few different kinds of star trails as you may have seen in different images the stars often look different, they swirl in different ways, this is not the stars acting differently, in fact depending where in the sky we point out camera we get a different result.
These are the kind of star trails possible
In The Northern Hemisphere:
North Star Trail
Equator Star Trail
In The Sothern Hemisphere
South Star Trail
Equator Star Trail
Myself being so far in the Northern Hemisphere will never get a south star trail from my current geographical location, it's physically impossibly because when I look in to the sky I can only face the North Pole, and vice versa people located in the Southern Hemisphere will only able to get south star trails from their location, but The north/south star can even be seen slightly south/north of the Equator because of atmospheric refraction. As far as the look goes a north star trail and south star trail will look very similar, the stars will all circle around the north/south star. If I were to be any higher north getting an equator star trail would be very hard because of the curvature of the earth. In theory people living on the equator theoretically should have visibility of both North and South stars, weather or not they are clear enough or in view is another matter. Equator star trails are very different from pole star trails, where north and south pole trails curve around the poles, the equator trail does neither, the lines are perfectly straight and this only really occurs right on the equator, then will then see either side of the equator the stars will star to curve towards the poles once again, which can make for some very interesting images.
The image below like the other is an example of a north star trail.
A star trail is essentially what it says in it's name, a trail of stars in your picture. Now these trails can't be seen to the naked eye because they don't actually exist, we create them by using our camera and long exposures. By pointing our camera at the stars and using a long exposure what happens is the earth continues to rotate on it's axis with us on it, and the stars remain still in the sky, our sensor picks up any light in the dark, the stars are a form of light, small and not very bright but enough to make an impact on the picture. This little bit of light in our image then streaks across the sky as the earth turns. The length of the trail usually depends on how long we leave our shutter open for. 30 seconds will get us the small dots in the sky, which in the correct location can look very impressive. 5 minutes will get us a very short trail, even 30 minutes doesn't produce massive star trails. I usually leave mine for at least 30 minutes and usually 1 hour maximum. I have done a few that lasted a few hours but they sometimes look a bit much. The image below was a 30 minute Star Trail.
StarStax can be found here -
Star Trails can be found here -
Before we finish I shall quickly run through how to edit your stack well, there is nothing worse than a badly edited stack, some times you can give away your stack by bad editing. So here is the quickest and easiest way to edit a stack together.
I use Star Stax and Photoshop to edit my stacks together and there is a good reason why. A bad stack usually consists of the static stars from the lighting shot mixed in with the star trail, so you would get a dot then a line in your stack, this gives away the stack and makes a bad trail.
Open up Star Stax, and then click open, and select all of the images that your stack will consist of, except the lighting shot, so when you click process it will stack them all together and it will look a little something like the image on the right.