This is one of those exercises that, while a little boring to do, can make those valuable lens investments worth so much more. Fortunately, it’s something that only takes about 10 or 15 minutes to do, and when it’s done, you’re all set. That exercise is finding the “sweet spot” of your lens. Essentially, figuring out at what aperture it performs best and gives the sharpest, cleanest results.
This video from photographer Mark Denney walks us through the process. How to shoot the images and then what to look out for when analysing the results. This way, when you depend on your lens on a real shoot, you’ll not be wondering why your images are soft.
As you can see in this comparison from the video, even when the lens is perfectly focused on your subject, the aperture of the lens can make a big difference when it comes to how sharp the image is. Too wide, and it’s just soft. Too small, and you may start to see diffraction issues – also causing softness. The Sweet spot is that happy balance in the middle where it’s at its sharpest.
The basic process is pretty straightforward. Although, like I said, it’s fairly boring, too. But it doesn’t take long to do. Shoot the same image over and over again at different apertures, and then look at them 100% on your computer. It’s really that simple.
Sure, we’re digging into pixel peeper territory a little here, but it’s something you only need to do once with each new lens you acquire, and you may be glad you did.
You have to make sure that the shots are as identical as possible, and that your camera is as steady as possible, and that your focus distance doesn’t change. This means setting it on a tripod. You may also want to use your camera’s mirror lockup or delay mode if it has one, and a remote shutter to fire it.
As Mark mentions in the video, as you go through the results to determine which apertures give you the best results for each lens, jot them down so that you have them handy. Eventually, you’ll just learn to know and understand your gear, and remember which focal length & aperture combinations give you the sharpest results.
Sometimes (perhaps even often), absolute sharpness doesn’t matter. But for those times when it does, you’ll be glad you checked ahead of time.