The images here may speak otherwise, but this post is not about NEOWISE. Instead, today I’m going to talk about image stacking. If you’re not a photographer, this topic may not do much for you, but read on and you might find it interesting. It might also give you some insight into how photographers deal with some of the limitations of photography in today’s digital world. Photographers have been dealing with the limitations of photographic techniques since the invention of the medium in the 1800s. In this regard, digital photography still has many of these same limitations, but some of the tools available today offer extraordinary control over the image-making process.
Image stacking overcomes many photographic limitations. Some examples include the use of separate images to create a panorama. Our phones do this for us automatically, but you can also do it with separate images from a DSLR. Exposure is another reason to stack images. This is the high dynamic range (HDR) technique that everyone has undoubtedly heard of. Our phones also do a remarkable job of this even when we don’t use the HDR setting.
One of my favorite reasons to stack images is to reduce noise in night sky images. Electronic noise in an image results from several factors that we won’t go into here but suffice it to say that noise is probably the biggest challenge when it comes to night photography. The cool thing is that image processing software offers unique solutions to this problem. I had a recent example with the comet that illustrates this nicely. I’ve attached two images to the bottom of this post. One shot has tons of electronic noise that you can see as mottled green and magenta specks in what should be a smooth sky. Not good! The other shot lacks the mottled noise patterns and has a nice smooth sky. Good!
Here are the details of the images. Both were shot with a Nikon D850 at f/2.8, 4 sec, ISO 3200, on a focal length of 105 mm on a stationary tripod. I acquired a total of 48 exposures of the comet. I used a software package called Starry Landscape Stacker (SLS) to stack all the images. The cool thing is that SLS aligns the separate exposures to correct the apparent movement of the stars due to the earth’s rotation, but it doesn’t affect the foreground. (There is a foreground in the uncropped versions of the images). If you’re into this kind of imaging and you use this technique, then you understand how powerful it is in overcoming the noise inherent in digital image files. If have never used it or think it is too complicated, it is not as difficult as you think. The results can really be worth the effort!!