Tuesday 13 August 2013

Theewaterskloof Dam

Theewaterskloof Dam after Dark - Canon 40D, Tokina 11-16, 20x30sec, f/2.8, ISO 3200
Theewaterskloof Dam lies just over the Franschhoek Pass. When it was established in 1978, it flooded a number of trees, whose bleached skeletons can still be seen poking out of the water. Some of them can be found on the sandy shores of the dam, depending on water levels, and make excellent photographic subjects. For example, The Eye of Sauron (mentioned in my previous post on infrared photography) was taken there back in 2011.

I arrived there late one afternoon a few weeks ago, just in time to catch the last light on some of the trees. I blundered along the swampy shore (it had been raining heavily earlier that week) and tried to reach the trees I had photographed two years ago, but in the gathering dark I eventually gave up and turned back. Next time I'll bring gum boots!

As the last of twilight faded away, the only remaining illumination was the light pollution from Franschhoek and Stellenbosch behind the mountains - and from the Milky Way, which was rising in the East.

I set up my tripod and panoramic head and took a series of 30second exposures at ISO 3200 (the highest my old 40D can manage) and f/2.8, which I eventually stitched into the panorama above. I'll show you my post-processing below. It's quite similar to how I made the Quiver Trees by Night series.

Last Light - Canon 40D, Canon 70-200 f/4 IS, 130sec, f/11, ISO 100, ND filter



Composing a panorama is difficult, since it is very hard to visualize what a 270 degree view will look like compressed on a single page - that is simply alien to the way we normally see the world, which is why ultra wide-angle panoramas can be so striking. There are a few tricks worth knowing, though.

First, parallel lines in the sky get turned into arch-shaped structures in the final panorama (assuming a equirectangular projection or similar). Such patterns may by quite subtle, often just a statistical asymmetry in the random pattern made by clouds - the linear structures aligning parallel, or sometime perpendicular, to the direction of the wind. But in a panorama, these arches can become quite obvious, as in the image at the top of the post. The lines in the clouds here were parallel to the shore of the lake (that's just dumb luck on my part), and so the feet of the main arch stand nicely above the edges of the water.

I set up my camera at the point on the shore nearest to the stumps, so that way the stumps would end up in the center of the distorted image of the lake, and thus also directly beneath the arch in the sky. On my way there I had hoped that the Milky Way might arch over the whole scene, but it was still early and the Central Bulge was just rising in the East. I was again lucky in that it is nicely balanced by the brightest region of light pollution in the West.

Once again, this shows that light pollution - hated by most astrophotographers - can contribute something essential to the composition. 


I didn't do any. I just found myself with a free evening, packed my gear into the car and drove off. I was mostly lucky to get this shot. I really should have done my homework, though, and with wonderful free software like Stellarium it is child's play to predict exactly where the stars and moon will be at any time and location.


 I always shoot RAW (for maximum flexibility), and import the images into Lightroom. I had made 20 exposures, covering almost the entire sky. I had learned from previous experience: rather include too much than too little, you will crop a lot anyway.

The 20 exposures in Lightroom

I made some basic adjustments in Lightroom: Pulled down the highlights (the highlights actually clipped in the brightest part of the cloud on the right - I should have been more careful), raised the shadows, and set a very low color temperature white balance to better contrast the orange light pollution from the blue stars.

I then exported the images as 16-bit TIFF files (so as to keep all color information for Photoshop to work with).

Next, I loaded the files into Hugin, my favorite (though quirky) panorama stitcher. Hugin does a very good job at finding control points (pairs of points in separate exposures that should coincide in the final panorama), especially in starry skies. But since I had such high noise levels in my exposures (ISO 3200 with shadows additionally lightened), Hugin's built-in control point finder struggled a bit with the darker regions. It's also quite bad when control points are added in the clouds, since these move from shot to shot - especially during a 30 second exposure. So I spent some time adding control points mannually.

In Hugin
Eventually, though, I got a reasonable set of control points (for a while I was puzzled by two shots which didn't match well with the rest - it turned out these were two single pictures I had taken earlier some distance away. I threw them out - they are not part of the 20 shown above). Next, I got to prod and pull at the panorama in the quick preview window until I got the surface of the lake horizontal (that actually required a complete redo of the image. I had already printed it when I realized that what looked straight actually wasn't), and I got a framing I liked - with the tree stumps dead center, propping up a nice symmetric composition. The Rule of Thirds is made to be broken!


Once Hugin had finished stitching a nice 16-bit high resolution panorama, it was ready for Photoshop.

Before Photoshop
Okay, so this doesn't look quite as different from the final product as my Quiver Trees by Night did. A few things were still amiss, however. The brightest bit of cloud was overexposed and featureless, and much brighter than the left hand side, upsetting the overall balance. The tree stumps were too dark. The Milky Way barely visible, the color balance still looked too warm and the image lacked punch. Time for some magic.

Adjustment layers in Photoshop

These are the adjustment layers I made. As you can see, my weapon of choice is the Curves Adjustment, masked so as to affect only certain portions of the image. Curves gives you the finest possible control over contrast, and I also use it for lightening and darkening, instead of the dodge and burn tools.

Tone curve for tree stumps
This is the tone curve I used to lighten parts of the tree stumps. The curve is very steep in the darker tones, giving a strong contrast here. You pay for it by losing the highlights, but there aren't any in the stumps. To draw up this curve, I selected a small rectangle in the image containing about half of the stumps, then created the curve adjustment layer. Photoshop automatically turns the selection into a mask for the adjustment, and I modify the curve while watching what happens in the rectangle, especially compared to the rest of the image, which remains unaffected. When I have the effect I want, I pour black paint into the layer (making the adjustment invisible) and start subtly painting with white (at about 10% opacity) onto the layer mask above the stumps. This way I slowly lighten bits of the stumps until they looked about right.

Darken the clouds
 Next, I did pretty much the same to darken, and increase contrast in, the brightest clouds. If you carefully look at the histogram above, you can see the precipitous drop at the right - this is where the highlights were clipped, then pulled down a bit in Lightroom, but the information was already lost. Usually there is more headroom in the RAW file, but at ISO 3200 the dynamic range is quite low.

Increasing contrast in the Milky Way
After that, I did the same again to increase contrast in the Milky Way. As you can see from the histogram, almost all of the selected portion of the image falls in a narrow band of tonality, and I made the tone curve steepest here, which means high contrast. That's the beauty of the tone curve: height above (or below) the diagonal tells you how much you are brightening (or darkening) certain tones, whereas the slope (for my students: the derivative!) indicates the contrast.

Darkening edges and corners
I also used a tone curve to darken the edges and corners of the image. This helps to keep the eye from wandering out of the image.

One layer I had better explain is the "faked texture for blown bit". This is a transparent image layer onto which I cloned a bit of texture onto the blown bit of cloud from the surrounding cloud. I just selected as source the bottom layer and then painted onto the transparent layer with the clone stamp. This way I could control the opacity of the layer and thereby adjust just how much fake texture to introduce. I tried not to overdo it. Here are the before and after pictures of that portion of the image.

There are two more layers. One is a Photo Filter, which is just a cooling filter (can somebody please explain a more convenient way to adjust white balance in Photoshop?) used at low opacity. The other is my watermark - a simple text layer - which I use to protect my images on the web.

Some more pics

Well, that's it. Here are a few more images of the Theewaterskloof Dam (taken during a full moon outing with the Helderberg Photographic Society), as an apology for neglecting this blog for so long. My excuse: I'm holding my inaugural lecture on Thursday, and that takes a lot of preparation. Enjoy!

I really need to lay off the colors in my HDRs...



  1. Florian
    I haven't seen a more comprehensible explanation of lightroom/photomerging techniques. I will save this page to learn more.
    Besides star Picture is beautiful.

  2. I cannot begin to thank you enough for what has to be one of the more comprehensive detailings for astrophotography. I have a similar set-up with my new Nikon D5100 and I am really looking forward to taking some night sky photos. This page will help assure I do something worth showing.

    Thanks again! (These are great pictures too, by the way!)

    1. Thanks for your comment! I'm glad you (and Mr. Anonymous) find this helpful. With D5100 you should actually get slightly better image quality than I do with the venerable 40D...

  3. Yes photography is an also use to capture enjoying moments but videography is capture enjoying moments in every poses.
    Video grapher in jaipur

  4. I have a similar set-up with my new Nikon D5100 and I am really looking forward to taking some night sky photos.

  5. Thanks for the detailed and very helpful post. I saw your photo in country life which led me to your blog. I must say that although I am no professional, I feel you were robbed of first place.

    1. Thanks, Gary! Actually, I'm quite happy with 2nd place in Country Life...