I am fascinated by the night sky – there is something indescribably beautiful about a clear night sky when all the heavens are visible. I used to be disappointed with my ability to create photographs that accurate represent the way viewing a beautiful starry night sky feels, I overcame this with a little digital magic and a technique that I call “Stitching the Stars.” This is a powerful technique that allows you to make wide-field astrophotographs with very low noise, high signal and enormous resolution. This last bit is key, because I want to make huge photographic prints of these images and not be looking at a grainy, noisy print. Because these images are composites of many smaller images, the savant astronomer may be able to detect small distortions in the night sky. The rest of us, however, will be left with an incredible image and the question – how did you do that??
The world is awash in starlight at all times but is also rotating at a dizzying clip, meaning that the source of that starlight is streaking across the sky at all times. Although star trail photographs can be breathtaking when done properly, our eyes perceive the stars as fixed points, and in order for our cameras to collect enough starlight so as to make images that recreate those points, we have to increase the sensitivity of the camera’s sensor, thereby decreasing exposure time but increasing noise considerably. Ultimately, the goal should be increasing signal to noise and, therefore bumping up the ISO is not the best option. Nowadays, DSLR cameras have high ISO performance with low noise. For example, my Nikon D700 can produce images at ISO 3200 with noise levels below what those my old D100 produced at ISO 800. Moreover, the D3s is rumored to another stop or two more sensitive with the same low noise performance – I can only imagine what kind of images one could church out with that tool and this technique.
1.) Visualize the final image
The trick to any panoramic photograph is to visualize in your mind’s eye where the photograph stops and starts. The software described in this tutorial (which is available for FREE!!!) allows you to stitch any number of photographs together into a larger image. The temptation may be to include EVERYTHING in the frame. Take my word from experience, this is not a good strategy – a great photograph focuses our attention on the subject. So then, visualize what you are going to cover and compose in your mind how you are going to frame it.
2.) Take the images
It should be mentioned here that you’ll need a tripod – this should go without saying as your exposure times will be so long you’ll absolutely require a tripod – but moreover, you will need the camera to stay fixed so the images line up properly. Now that you’ve visualized what you are going to cover – add 10% on each side. As you will see, the process of stitching these images together means you lose some of the image on the edge – you will therefore lose those photo elements that are on the edge of the outermost frames. You want approximately 20% of each image to overlap with the images above, below, to the left and to the right. This will give you adequate opportunity to align elements between the images so as to create a seamless blend. You should note this can be done with just about any camera, including a point and shoot with a manual function. In fact it should be said that this technique is PERFECT for squeezing high quality astrophotography from an inexpensive camera. In any case, find that 15-30 second images at 50mm f/1.8 ISO 2000 is *juuuuust* about right for an exposure of the Milky Way on a cloudless North Dakota night. Here are the images I took for Light Years arranged in photoshop in the relative positions they were captured. You’ll notice at this point we are about 80% of the way there – but we need some help from a computer program to complete the proper warping and blending to make this image seamless.
3.) Process the images
This is really up to you. My Christmas gift this year was a really cool astrophotography program that allows for the proper processing of images like these. I can’t wait to take some images and try it out – but for the meantime I’ll tell you that the images for Light Years were given a very slight contrast bump and a white balance adjustment (daylight).
4.) Align the images using Hugin
Hugin is an incredible program. It is a frontend for Panorama Tools, which has so many uses that listing them here would take all day. Let it be said that Hugin can line up your images and blend them into a panorama seamlessly. The first step is to load the images into Hugin:
You may then need to provide information about the lens and camera – this allows the program to warp the images so that many images taken from a fixed point can be stitched into a single frame. Here the program is told the images are shot with a 50mm lens on a full frame sensor:
Hugin will now use a program called Autopano-SIFT (a part of Panorama Tools) to match features of each image together. Sometimes, the program can have trouble doing this. In this case, the program was unable to match any of the images together. Instead, I had to provide this information by linking each image with its neighboring images with at least three “control points”:
The program can then optimize these control points by searching nearby pixels to see if any match up more accurately:
Properly lined up, you can view the panorama and begin to make adjustments:
You’ll notice that the panorama above is twisted and uneven. Luckily, Hugin can accurately correct for these errors – just click the “Straighten” icon at the top of the panorama editor window and now things are looking much better:
Now that the panorama is straightened, you should click on the horizon. When you line up the horizon properly with the center of the panorama, you’ll notice the shape, size and perspective of objects in the frame are all in order:
5.) Create the blended panorama
Finally, it is time to stitch the images together and create the panorama by clicking Stitcher, then the button that says “Calculate Optimal Size.” Click “Stitch now!” and sit back as Hugin generates a blended panorama image. Voila! – you are done.
I would love to see what you guys do with this technique – if you ever use it – send me a link to your awesome work, I’d love to see it – Cheers!
Photo by Justin Kern – Feel free to use images with links and credit – no commercial use without permission.