Photographing the Milky Way in the Cederberg

A week ago I got the opportunity to spend a long weekend in South Africa’s Cederberg Wilderness Area. While there, we enjoyed two cloudless nights, during which the stars were exceptionally bright. In fact, in this remote part of the world the stars are always exceptionally bright compared to the cities we may be used to.

Here is one of my favourite shots, stitched from 16 individual photographs to cover the Milky Way from horizon to horizon:

The bright yellow glow on the horizon, to the right, is the town of Ceres. Even though it is a small city of 33,000 people, and hidden behind a mountain, its light was enough to affect this photograph. You really, really, need to be far away from the cities to get any good astrophotography done. This is, sadly, becoming more and more difficult as humans fill up the Earth’s surface.

This photograph proves that one can get great results, even when working with gear that isn’t the very best that money can buy. In a previous post I talked about how certain DX lenses can be used in FX mode: this photo is proof of how this can work in practice. The lens I used was the Tokina 11-16mm f/2.8, set to 15mm where it (barely) covers the full FX frame. To be sure I would have been better off with the Nikkor 14-24mm f/2.8; a lens I desire. As it is I do not own this lens, and got al result that I am still very happy with.

Pointing the lens straight up towards the sky and setting it to its absolute widest setting (11mm), one clearly sees that it does not cover the whole FX sensor. Futhermore, one sees that even in the areas that are illuminated the image quality and light falloff suffer as one approaches the edge.

When one reaches 15mm the situation improves markedly, and even gave very good results from an overall photographic standpoint.

Pixel peeping in the upper-right corner of the photograph above, we see that the lens’ performance suffered and created some funky cross-shaped artifacts.

One also sees the high amount of noise that the sensor inevitably captures at ISO6400. This will probably not be useful for large printing. However, looking at the complete result on typical viewing sizes, the result was breathtaking. This isn’t the Hollywood silver screen, or a Pixar animation studio. This is the real night air, close and simultaneously infinitely far and real. With our naked eyes we see light years to the core of our own giant spiral galaxy. Despite its vastness, this galaxy represents just a tiny tiny fraction of the sheer vastness of the known universe. It gives a clear reality of us being part of the cosmos – right here where we are; without having to go into space.

When you photograph heavenly bodies, you need all the light you can get. This is why I used F/2.8 lenses, shot wide open at F/2.8. You may ask why one would not then use a lens with even faster aperture. Indeed, I took out my 50mm f/1.4, and took the following shot:

The longer focal length enabled more detail of the Milky Way’s central region to be visible. The downside of the longer focal length is losing the horizon that gave some context of what we see in relation to us, the viewers. The larger aperture enables a lower ISO value and/or shorter exposure time, but also magnifies the motion of the stars. Because the Earth rotates, the stars seem to move from East to West across the sky. This movement may look slow to the naked eye, but with a high resolution camera one can see this motion as blurring in an exposure as short as 10 seconds. If you double your focal length (e.g. from 25mm to 50mm) you need to halve your exposure time for the same amount of motion blur, negating much of the advantage of the larger aperture.
Even though I shot the 50mm at f/1.8 where it performs better than at f/1.4, you still see that the stars in the image corners are distorted due to the lens’ astigmatism. Luckily, when you create a panoramic image like at the top of this post, the corners matter less than you may think.

Let’s get back to how I created that big-picture panoramic image at the top of this post. For this I first took a series of 16 photographs, each in itself a 15mm wide angle photo:

The next step was to use the excellent, and free, panorama stitching software called Hugin to stitch the images together. Although Adobe Photoshop and Lightroom contain panorama stitching functionality, it is not capable of handling such a complex panorama spanning a very very large field of view spread out over multiple rows.

After determining the relative orientations of the images, Hugin allows you to select the intended projection, and then warps each image to match the chosen projection and its final position in the panorama:

These sixteen warped images overlap significantly, allowing the final image to only include the more central parts of the images where the lens distortion is manageable. Hugin is very clever software, and can also correct for differences in image exposure between the input images. The end result is the image at the top of this page.

I’d like to end with a video created by Ian Norman and Diana Southern where they reflect on the process of capturing the Milky Way and night sky through astrophotography. Beautifully montaged, it was recently featured on National Geographic. I hope this leaves you inspired, and willing to try your own hand at this type of photography. These heavens are out there, accessible to us all. Every cloudless night.