With sunny days and if you have the opportunity to move away from large urban centers and light pollution, summer is particularly adapted to watching stars and thus to taking night shots!
In line with last month post about this amazing timelapse of our planet seen from ISS, I wanted to share with you my first experience of star trails photography and time-lapse, a 2 in 1 tutorial somehow. Besides being a very pleasant exercise, you will learn a lot about how to use your camera in extreme conditions, how to shoot at night, and most importantly how to manage noise in extreme conditions.
If you want to shoot a nice star trails, there are basically two techniques:
You may have already seen this kind of images, where the stars leave a beautiful colored circular trail, this is called a circumpolar star trails.
- take a single shot with a loooooong exposure time (like> 40 min)
- take lots of pictures at regular intervals and then assemble them ‘( stacking method ).
Both methods have their advantages and disadvantages. The first requires less hardware and finally less work in post-processing. However, you have to keep in mind that it can very easily fail and make you waste hours (a car headlight, a blow of wind, a battery issue and your photo is ruined…) and most importantly, this technique generates a lot of noise in your image.
We will concentrate on the second technique. You will need a control device (not tested but is should be manageable by hand if you are patient and disciplined) and a post-processing software. In addition to not having the disadvantages of the first method, this technique also allows you to have a foreground subject properly exposed and to make a movie of your pictures, isn’t life great?
Some basic requirement for shooting stars
What equipment is needed for star trails photography
For this exercise, you will need:
- a tripod (essential)
- a camera with a manual mode or at least that lets you choose a long exposure time (> 15s). Ideally, a camera with a BULB mode.
- basic notions of astronomy
- a control device for triggering the camera. In my case and as I don’t have an intervalometer, I used my laptop, a USB cable and EOS Utility, the software that came with my Canon. It basically gives you the possibility to control and program your camera.
- a flashlight which is convenient for orientation in the dark and that could also be used to lightpaint your foreground.
Astronomy 101 or how to find the fixed point ?
It is not necessary to have a PhD in astrophysics, but some very basic concepts of astronomy are quite useful. The apparent motion of the star is due to the Earth rotation. In the Northern Hemisphere, the North Star (Polaris) is in the axis of rotation of the planet, therefore, it will appear as a fixed point around which all other stars will appear to rotate. In the southern hemisphere, locate the Southern Cross. Here’s how to find the Northern Star.
- You have a smartphone: Download an app (randomly Sky Map on Android, Star Map on iphone). It works great and it takes 3 seconds to find what you need.
- You are more the adventurer/romantic/poor: type. Polaris is the brightest star in the Ursa Minor constellation. If you know roughly where the North is located, this is the direction to look. First locate the Big Dipper. In early summer night (2-3h after sunset), it appears rather low in the horizon. It is recognizable thanks to its famous pan form. Once found, simply follow an imaginary line that would pass through the two stars forming the tip of the bowl. At about five times the distance between these two stars, you’ll come across Polaris. Polaris is the tail of the Little Dipper, or in other words, the extreme point of the handle.
The Southern Cross is more difficult to locate, and I did not have the opportunity to exercise, have a look here for more information.
Advantage of a wide angle lens and the 500 rule for photographing stars
Any lens can be used to photograph the sky but it is best if it has a wide aperture (low f) in order to reduce exposure time (and hence noise), and it is much easier to take picture with a wide angle for two reasons:
- It is not always easy to compose a picture in complete darkness. With a wide angle lens, you can be almost sure that everything will be in your photo. You can then crop your shot in post-processing. This is basic but it is true.
- Stars move very quickly! And the further it is from Polaris, the faster it moves. It may seem to be counter-intuitive at first, but I assure you that depending on your viewing angle, if you take a 30s shot with your kit lens, the stars will not stay still. OK and the wide angle then? Well it’s simple, the closer you look, the faster it seems to move…If you’ve ever watched the moon with an amateur telescope, you can see exactly what I mean.
There is a simple rule to determine the maximum exposure time you can set if you want to freeze the stars. Divide 500 by your focal length in 35mm equivalent (multiply by 1.6 if you have a Canon croped sensor, for other model check it here).
For instance, with a 35mm kit lens on your EOS 500D (small sensor), this gives 500 / (50 * 1.6) = 6.25 seconds! It’s fast…
If you want to make a beautiful timelapse, where time for each image seams to be “frozen”, it is necessary to comply with this rule.
How to shoot stars trail
Composing your photography
- Locate your still point and position it in your composition.
- Make sure your tripod is stable.
Setting your camera and choosing a lens
- You should prioritize short focals, if you have a wide angle, use it.
- Set your lens in manual mode (MF) and set the focus to infinity.
Take a shot with your foreground properly exposed. This image will be used to combine a well exposed foreground with the star trails. You can use your flash or maybe your flashlight to illuminate your subject.
Settings for correctly exposing the stars
- All your images will use the same settings, so set on the Manual mode. The idea is to have an aperture as large as possible (small f), ISO as low as possible and exposure time respecting the 500 rule. Do not worry about your foreground, we want the stars now. In a moonless night, 400ISO, f4.5 and 30s worked quite well but you can set higher ISO (800 or even 1600 if your camera device is recent) if you want to reduce the exposure time. Try different combinations, there really is no magic formula. The only certain thing is that high ISO and long exposures will give you more stars and more noise…
- Set off the automatic noise reduction for long exposures if your camera has this feature. On one hand, the noise control is always more effective in post-processing and secondly, on the other hand, because this features works by doubling all your picture by a ‘negative’ equivalent, your device will be unavailable between each shot. In other words, if you leave this option, your trails will be dashed.
- Instead of using the in-Camera noise reduction function, we’ll do our own hot-pixel detection and use it at post-processing. Without changing your star settings, put the cap on your lens and take picture.
- It is not necessary to make complex calculations to find the best combination between your number of shots and the timelapse framerate. A very fluid timelapse is at nearly 20 images / s, however, I found the final result to be quite decent at 2 frames / s.In all cases, it is important to caliber your session based on the real time you’ll be shooting the stars and to adapt your sampling exposure time accordingly. The longer the session, the longer the trails. With only 30 minutes, effects are quite pronounced as you can see in the picture 3.
- Minimize the time between each shot! With just 6 seconds of delay between two shots, the streaks will not be perfectly continuous.
- Launch the sequence and do not touch anything, read a book, watch the shooting stars …
- Once your photo series is finished, take another hot-pixel picture, ie, put the cap back and take a photo with the same settings.
Post-processing, stacking and timelapse
Creating a stacked image
- Make your adjustments (brightness, contrast, balance …) with your usual software on a photo of your series.
- Replicate your adjustments on all photos. Most programs allow you to do these mass corrections. In Aperture for example, find the option for Taking and Applying metadata , with Canon DPP, the option is called Copy recipe . Look at your manual if you don’t find the option.
- If you worked in RAW, export all your photos to JPEG.
- Put all the post processed pics in the same folder.
There are several stacking software, I used StarStax , it is a simple, multiplatform and free software.
The software can’t be easier to use:
- Load the folder containing your star trails photos but not your foreground.
- Load your hot-pixel negatives (2nd icon from the left ).
- Specify the export folder.
- Make sure that the Lighten and Subtract Dark Images options are checked.
- Start the conversion and watch the magic!
- Now, you just need to add your well exposed foreground, either with StarStax or with any other photo processing software.
Creating a timelapse
Note that StarStax has a Cumulative saving option, which allows you to save each stacking step. If you make a timelapse with these outputs, you’ll get another cool effect.
OK, I agree, this is not exceptional from an artistic point of view but it was not really the purpose of the first session. You have to admit though that the basics are definitely there !
Finally, and for inspiration, here is a small selection of Flickr photos taken with this technique. Note that a photo shot at dawn or dusk can add a wonderful supernatural effect .
Time to practice now…between two shooting stars …