Lenses these days have all kinds of aperture ranges, with some opening as wide as f/0.95 and others stopping down as much as f/32. But shooting at either extreme can cause potential issues. At the wider apertures, those issues are obvious. The shallower depth of field can mean you don’t get enough focus to get everything you need looking sharp. And most lenses are a little soft wide open anyway. Then as we stop them down, things get sharper. But is there a limit? Well, yes. With many lenses, as you start to go past f/11, you’ll see things will become soft again. This is due to something called diffraction. We’ve covered diffraction here on DIYP before, a couple of times, actually, but it’s always good to have a reminder, and this video from Matt Granger does exactly that, explaining what diffraction is, what causes it and how you can prevent it (by basically not stopping down smaller than f/11).
You might have noticed that you get to a certain point with your lenses that when you keep stopping down, your images get softer again. When digital cameras were still in the 16-megapixel or lower resolution stage, diffraction wasn’t that big of an issue a lot of the time. It was still there and noticeable if you really pixel peeped, but you could still often get acceptable sharpness (although “acceptable” is subjective) at beyond f/11. But as camera resolutions have increased to 36MP, 45MP and even higher resolutions, diffraction has become a lot more noticeable and a bigger problem for photographers.
Diffraction potentially explains why Canon’s recently released Canon RF 600mm f/11 IS STM and Canon RF 800mm f/11 IS STM lenses have a fixed f/11 aperture. Having a maximum aperture of f/11 means they can make the lenses small (and inexpensive). But with the potential diffraction issues, there’s really no reason for a lens that already has such a small aperture to really let you go any smaller. And having a fixed aperture also means less engineering and also helps to keep the costs down for the consumer. I mean, what other 800mm prime lens can be bought from a reputable brand for less than $1,000? It can be tough sometimes finding that balance between giving you enough depth of field and an acceptable level of sharpness. This is why many macro and landscape photographers often resort to focus stacking – even if stopping down to f/22 or f/32 would give them the depth of field they need in a single shot. Ultimately, it’s all about keeping that detail sharp throughout and not just whether or not it’s in focus. Do you constantly battle diffraction in your photography?
