One of my favorite things about the Olympics is the next-level sports photography we're treated to as all the world's best shooters gather in one place to capture the world's best athletes.
We've already seen some stunning images from Rio 2016. The most famous of these - and the one everyone will likely remember - has already been shot: Cameron Spencer's museum-worthy image of Usain Bolt grinning as he crosses the finish line a full pace ahead of his struggling competitors.
But I want to take a minute to highlight another image, the one at the top of this article. Its subjects, wrestlers Zelimkhan Khadjiev (in red, France) and Japan's Sohsuke Takatani (Japan), aren't as famous. But the technique and execution involved is at least as interesting.
Like the Bolt photo, this image involves some optical trickery and a slowed shutter. Spencer shot Bolt by taking the image over an unusually long fraction of a second and swinging his camera to follow the runners.
On the occasions I've attempted something similar, I've entirely failed to capture a single sharp face.
To make an image like this, you have to place your subject in the exact center of the frame and zoom in or out with the shutter open. If you want it to come out right, you have to hold your camera completely steady, all while shifting or twisting the zoom on your lens at a constant speed. It takes some dexterity.
And of course, the challenge to any photographer getting fancy in this way is that there are significant risks. As long as the shutter's open on your DSLR, no light reflects up into the viewfinder. So you shoot blind, and hope for the best. Fail to get lucky, or make a mistake, and you've likely missed the big moment of the match to send along for publication.
But Riedel captured a moment of high drama here, Khadjiev's leg flailing in the air as the two wrestlers grapple. It's a fantastic image, and stands out even among the other slow-shutter shots we've seen this year.