Diffraction made simple – Why your pictures are softer at f/22 than at f/8
It’s something that all of us have run into at some point or another, particularly when we’re still learning the basics of photography. We learn that when we stop down our lenses, we get more depth of field and a sharper image. So, if I need the most depth of field, I should just stop it down all the way, and everything will be in focus and super sharp, right? Well, no, not exactly.
Diffraction is a topic that gets thrown around a lot when people start talking about stopping their lenses all the way down, but a lot of people don’t really know what it means. They’ve seen the effects, but how and why does it happen? In this video, ZY Productions explains what diffraction is, and how it affects your images.
Diffraction is simply a function of how light works. It’s the way all waves work. If you could visualise sound in the same way that you can with light, you would notice it there, too. It’s a type of interference, and we can see it in the real world in many examples, like water rushing through a narrow opening in a straight line and creating circular waves on the other side. The same thing happens with lightwaves.
One simple fact that most people don’t realise about diffraction is that it actually happens at all aperture values. But its effect is so minimal at wide-open f/1.4 apertures that we can’t really see it. Softness at wider apertures is an issue, but it’s not due to diffraction. As we start to stop down, those other issues disappear, but diffraction still isn’t really noticeable even at f/8, which is why the image appears to get sharper. But by f/11, though, it can start to creep in and negatively affect our images.
The smaller we go with our aperture, the more obvious diffraction becomes. There’s no magic number as to exactly when it’ll start. It’ll vary due to multiple factors, like exactly which lens you’re using and the resolution of your camera’s sensor, but it will happen at some point, and it happens to all lenses, no matter how expensive they may be.
So what options do you have if you need more depth of field, or your exposure is still too bright at f/8? Well, for the former, you can try focus stacking – diffraction is one of the main reasons it’s so popular amongst landscape photographers. For the latter, well, that’s where neutral density filters can come into play.
Did you understand what diffraction was before watching this?
John Aldred is a photographer with over 20 years of experience in the portrait and commercial worlds. He is based in Scotland and has been an early adopter – and occasional beta tester – of almost every digital imaging technology in that time. As well as his creative visual work, John uses 3D printing, electronics and programming to create his own photography and filmmaking tools and consults for a number of brands across the industry.