Sure you’ve seen pictures like that illustrates this article and maybe you wondered how you call these images so spectacular in which the trail of the movement of the stars can be seen (star trails) circular. They are called circumpolar photographs and they differ from others in which they also appear stellar traces in which they are made facing north (or south if you live in the southern hemisphere), so that you can capture the feeling that all the stars rotate around the polar star.
The technique to achieve a photo of these is, in theory, simple but “has its crumb”. In principle it is enough to plant the camera on a tripod, point the camera at the sky in the right position and leave it exposing enough time for the stars to move and that movement that passes unnoticed to our eyes is recorded in the camera. In principle the longer the better, but after five-ten minutes we should be able to capture a small trail of stars.
Of course, this is not so easy in practice; In fact, it is one of those cases in which chemical photography exceeds digital photography in terms of the ease of obtaining an image. Why? Well, it’s very simple, because with film, making a very long exposure is relatively simple; However, the same does not happen with the sensor of a digital camera that, as you know, is subject to a heating that produces different problems. Therefore, we are going to tell you how to make one of these photographs with your digital camera.
We have already advanced that you are going to need a tripod but it is also necessary to point out that one is not enough. That is, it is not that you need a special one for this kind of shots but it is important that you use one that is very stable and that you use it properly. Exactly the same as when you’re going to take a night-time or long-exposure shot, by the way, where getting the camera to not move in the least is crucial.
Therefore, in this sense it is also important to make sure we can press the trigger without producing vibrations , either with an app connected to the camera, with the delayed shooting of the camera or with a remote trigger, either cable or wireless. Even more interesting is to have an intervalometer that allows photos to be taken periodically according to a pre-set time and automatically (and therefore without having to keep an eye on the clock).
This possibility can also be included in the camera, which will make things much easier for us; but if not, it is enough that it allows you to make long exposures. That is, almost any camera will serve you, although of course the larger the less exposed sensor you will be to suffer noise in the image. As far as the objective is concerned, as you can suppose, you will need a wide angle that is preferably bright and of good quality.
For the rest, it is necessary to foresee that the camera is going to make a high consumption of energy with what we should be provided with spare batteries. Of course, taking into account that the camera should not move in the slightest, maybe having to change it will ruin your work so you should know how is the autonomy of your camera. If it is not enough for what you want to do, you have other solutions such as making a grip with an additional battery or, ideally, a power adapter to plug the camera into (if possible).
Choose the time and place
Once we are clear about the team, it is time to think about the place where we are going to make the shot because, as you can imagine, it does not work for anyone. First of all, as we have said, it has to be oriented north / south (depending on which hemisphere you are in) and it is also important that the sky is as free as possible from light pollution, so you should look for a place away from any light bulb; that is, normally as far as possible from the cities, but with the right orientation (north or south).
On the other hand, it is interesting to look for an isolated place but in which we find some element that contributes interest to the composition, such as trees, mountains, a house, a castle… As you can see in the photos that illustrate the article, If you include in the frame something more than the sky, you will make your photo gain attractiveness. Of course, it is not advisable to choose elements that may contaminate the light source, such as the skyline of a large city such as Madrid or Barcelona.
Once the site has been decided, it is time to choose the right moment,since neither is anyone. First, choose a night that is expected clear and in which there is no moon, for which you should check the weather forecast and the lunar calendar as for the time of year, there is no special recommendation, but think that it is possible that you spend several hours in the open so we do not recommend winter because the cold and humidity can be a problem (for you and your camera).
You are also interested in knowing that the height at which you should find the polar star will be different depending on the place on Earth you are on. If you are close to the equator you will find it very close to the horizon, while the closer you are to one of the higher poles you will find it. Consequently, if the photo is made from Spain, or from any country located at a similar latitude, the polar star will be at an average height of the sky. In any case, an application like Photopills will help you a lot.
Composing and shooting
Already on the ground touches plant the tripod with the camera and decide the composition , although as we will have studied the site in advance it is possible that we already have an idea about what we want to get. In any case, as we mentioned in the case of fireworks, and as we have said before, to avoid that the image is too conventional we must include other elements that add interest beyond what is seen in the sky.
It is time to focus, for which it will be better to resort to manual mode since the low light will surely make it impossible to use the automatic system. So, as a general rule, it is much better to put the objective in manual and focus to infinity . If in your image there are going to be elements at different distances, consider if you want everything to be in focus. It’s more a matter of style than anything else but if you want that to be the case, it’s time to take advantage of the hyperfocal distance to make sure you get the deepest possible depth of field.
To achieve this type of photos there are two techniques: an exposure as long as the camera allows us (without the sensor suffers) or make series of photographs that we will later stack
At this point, it will finally be time to start making the photograph, or the photographs because, although we have suggested it before, the most recommendable technique for making this type of images with digital cameras is based on the stacking of photographs. As it is not feasible to make an exhibition of hours, it is a question of making different shots of long exposure that capture the stars in their movement and, once united, reveal the traces of stars.
It can also be done with a single exposure, but as we have said the heating that occurs in the image sensor invalidates that this period is very long and causes a lot of noise in the image. In any case, it is interesting to know the capabilities of your camera in particular to see what you can get, in addition to testing how the noise reduction system works for long exposures that almost certainly incorporates. However, we already say that the best way is to make multiple exposures, especially since it is the way to get, with digital models, those long star trails that you see in the attached images.
Of course we will choose the RAW format and as far as the exposure values are concerned, it will be convenient to set the ISO to the minimum (to avoid noise when possible), to establish the diaphragm at the sweet spot (that is, at the value where the best quality is offered, normally two or more steps above the more open diaphragm), and choose a shutter speed between 20 and 30 seconds as a starting point ; although, as always, it’s a matter of trying.
There are ways to calculate the exposure to be made, but starting from about twenty seconds we can try to get a correct shot with which to start making our series of photos
With these values more or less we should get a photo with a trace almost negligible but that will become something else when we later assemble the series of photographs that we make. The amount of them to realize will depend on what we want to achieve , but we already say that with about five minutes we can begin to appreciate the movement of the stars. Logically, to obtain those skies with traces that form an almost perfect circle we will need to make enough shots, starting at 100.
As for the interval between them, the most recommended amount is between five and fifteen seconds ; that is, wait ten seconds (for example) before making a new photograph to be able to capture the stars in their movement without their traces suffer cuts between them. By the way, if you have opted for this system based on using multiple images, it is better to deactivate the noise reduction of the camera. It thinks that if it is activated, after exposing the photo the seconds that are, the camera will need the same time to process it and that can suppose a problem when trying to take many photos and does not allow time for the sensor to cool down. In addition, you should also have disabled the image stabilizer of the camera or lens.
As you can imagine, in this type of shots the processing of the photo is not only important, it is fundamental. What we do, yes, will logically depend on whether we have used the technique of a single shot or multiple. In the first case, the most important thing, almost certainly, is to reduce the noise that may have been produced in the image if we have not opted for the camera itself to do so.
If we have opted for the stacking of images we can assemble the final result with specific tools such as Startrails or Adobe Photoshop
If it is not the case, or we want to try to improve what the camera has done from the RAW file, a very interesting way to use the technique based on the use of a black frame, a very useful way in long exposure photo and which implies that during the taking of photographs we will also have to capture others with the same parameters but with the lens cap on.
And if we have said “other”, in the plural, it is because this technique is also valid if we are going to be based on a series of images; however, we would have to make many black shots which can be very cumbersome. So we better use another way to reduce noise based on the use of different shots as explained in the same article that we linked in the previous paragraph and where our partner Fernando (better known as “Ferfoto”) teaches us to reduce the noise.
The technique is done with Photoshop , which is one of the tools that can be used to “put together” the photos that should make up the final result, and in the process it explains how to do the Adobe software to stack the images.
If you prefer another way, this can also be done with specific programs like Startrails, a free software and quite popular (though perhaps it is already a bit outdated) that helps in the task because it is capable of binding the photographs say you of almost automatically . And with this we will have our circumpolar photography that, with luck, will not have much to envy to the ones you have seen here. If you dare, tell us about the experience.