A Simple Explanation of Why Aperture Affects Depth of Field
Film photographer and educator Tim Klein’s recent YouTube video explains the tricky concept of exactly why aperture affects your depth of field in a very digestible way.
In Klein’s video, titled “Why aperture affects the Depth of Field,” he takes to the whiteboard to break down this tricky topic with a straightforward visual. Klein shares that there are so many videos on f-stop or aperture that he never imagined creating a video on the topic. However, while chatting with some photographer friends, “the subject of aperture versus depth of field came up. And we all know that the aperture affects your depth of field… We all knew what it did but nobody really understood why aperture affects your depth of field. So we are going to try to explain that today without any math or physics and getting too complicated.”
So that is precisely what Tim Klein does. In less than 5 minutes, with magnets and red string, he quickly breaks down the concept into a practical and easy-to-understand format. He uses the strings to illustrate where light will enter a lens and hit the camera’s film plane. By moving the magnet indicating the subject farther away, and therefore altering the strings, he shows how the focus of the focal plane would also shift farther forward. This creates what is most commonly known as a circle of confusion (CoC), which he draws out as an oval directly over the film plane.
Some photographers may have heard the CoC called by other names such as the disk of confusion, circle of indistinctness, blur circle, or blur spot. Whichever moniker is used, the CoC is an exact optical area caused by the cone of light rays from a lens not perfectly hitting the film plane.
In Tim Klein’s diagram, the CoC was created by the subject moving farther away, but the camera remained in the same spot. Therefore, without moving the camera, the way to fix this would be to adjust the aperture of the lens. With a larger number f-stop, the opening of the aperture will narrow, letting in less light and changing the angle of that light as it enters the camera. This adjustment, visualized with the red strings, shows how the CoC gets smaller and smaller as the aperture narrows until, eventually, it is negligible. The result is a considerably increased depth of field covering a larger area front to back, therefore rendering the subject sharp.
With such a great explanation, the comment section is full of thankful photographers, from enthusiasts to professionals. As Tim Klein puts it he is, “Making Film Fun.”
Tim Klein is a problem solver and tinkerer by nature. Between his daughter’s flourishing interest in film photography and his own work with a 4×5 Super Graphic, Klein designed his own portable SP-445 film tank.
He calls it an “elegant solution for processing his own film.” Klein now runs an online store, named Stearman Press LLC, selling 4×5 large format photography film and processing chemistry. His company’s name is inspired by his passion for WWII and the Stearman bi-plane. It is a strong passion. Although they have since moved, he even started his company on Stearman Court at the Erie Airport, in Erie, Colorado. The desire to share his interests led Klein to create a YouTube channel where he explains complex photography concepts, film guides, and even his homemade photo inventions.
Image credits: Video by Tim Klein
