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Why focus stack when I can just use f/22?

I’ve got three good reasons why using f/22 won’t get you a sharp picture. However, even though I’ve proven these reasons in my own work, you should go try it yourself. The other day, I wrote a brief introduction to focus stacking (check it out here) and it has spurred a lot of questions and discussion on my Facebook page (including some guest pictures below). The major question posed there is “Why not simply use a small aperture to create a photo with great depth of field and get everything in focus instead of a process like focus stacking which requires post-processing to complete?” Everyone who commented about using f/22 to get focus throughout the picture has obviously never tried it :D

In focus ≠ sharp

Lots of people with Ph.D.’s in physics have written good articles about diffraction and why you shouldn’t shoot at the lens’s smallest aperture (I’m using f/22 to represent your lens’s smallest aperture, which may be smaller or larger than f/22). You should go read those. I believe them, and I’ve experienced the fact that f/22 often doesn’t produce the sharpest possible photo.

You can also read about hyperfocal distances which allow you to get everything in a scene in focus by focussing at a specific distance and a specific aperture/focal length combination. I made this photo using a hyperfocal calculator in the Field Tools app. This works well, and I’ve used it quite a bit. But being in focus doesn’t mean the picture will be sharp.

Nikon D800, 28-300mm f/3.5-5.6 lens, f/16, 28mm, HDR, ISO 400.

Many times we think our pictures are out of focus, but really they’re just not sharp, which means it doesn’t look as clear as we think it should be. It may be that it’s not sharp because of that diffraction problem, but it’s often not sharp because of motion blur. I’d wager that most of the time, the lens is fine and doesn’t require the “fine tuning” people like to spend so much time discussing. Like Scott Bourne says, “90 percent of lenses are better than 99 percent of photographers.”

Here are some examples from other readers.

Adam Hynes used focus stacking to combine several images together made down the length of this slot canyon.

Matthew Fry made these pictures of model trains and provided both shots that were stacked and shots made as single exposures for comparison.

Wayne Carey used 17 photos stacked together to create this picture of a fishing lure. He does this regularly as he makes the catalog photos for the Strike King Lure company, where he works. This is a great example of a well-finished focus stack.

Nikon D500, 60mm f/2.8 macro lens, f/11, 1/200s, ISO 100. Even with a small aperture, Wayne still used 17 shots to get this lure looking great.

Motion blur

When you use f/22 to make a picture, you are closing the aperture in the lens, the hole that lets light into the lens is physically getting smaller. f/22 is half as big a hole as f/16. That little hole means you need the shutter open longer to make a proper exposure, and that means two kinds of motion blur can become evident, ruining the sharpness of your pictures. You’ll get motion blur from the camera moving in your hands or even atop your tripod if it’s not stable enough, or you’ll get motion blur of the subjects in your picture moving while the shutter is open, like grass and flowers blowing in the breeze. I’m lucky that the header image here isn’t blurry at just 1/60th of a second and less for the HDR I made.

“How much slower is it, really,” you ask? Well, if I shot at f/4 instead of f/22, which is five stops different, the shutter speeds would be significant. At f/4 I could shoot at 1/200 of a second, and the software that stitches focus stacks together could work even if I handheld the camera.

The same picture at f/22 would require a shutter speed five stops* slower, though. That’s going from 1/200th to 1/100th to 1/50th to 1/25th to 1/13th to 1/8th of a second, and even if you use a tripod at 1/8th of a second you are likely to experience both kinds of motion blur. Using my Lumix cameras for focus stacking, they’ll shoot a scene at 1/200 of a second in less than a second and it works well.

*Yes, you could increase the ISO to get a faster shutter speed, but then you’d complain about noise in your photo. Do I really need to write another paragraph about that? :)

Close up & macro

The last example of f/22 just not working is when you photograph close to things or especially when you are doing true macro work. The fact is that the closer you focus–the closer your subject is to the camera–the shallower the depth of field becomes. Try this: set your camera on the tabletop and set two cups on the table. Switch your lens to manual focus and move the focus ring so that it is focussed as close to the camera as possible, then move the first cup until it is in focus. Then set your lens to its smallest aperture, like f/22, and you’ll find that the farther cup is not in focus.

Now, if you use a fisheye lens to do this, then the farther cup probably will be in focus because while focussing closer to the lens makes the depth of field shallower, using a shorter focal length makes the depth of field deeper–14mm has more depth of field than 100mm at the same aperture and focal distance.

When I used to use the Nikon 105mm f/2.8 macro lens, I could focus very close to the lens, stop the aperture down to f/45, and still only get a very small slice of a flower in focus. When you focus closely, a small aperture is inadequate to get the whole scene in focus, and focus stacking is a good way to overcome that problem.

Conclusion

Focus stacking is the way to overcome three problems that keep your photographs from having everything in focus. It allows you to use an aperture which is not limited by diffraction, it conquers motion blur by letting you keep a fast shutter speed with a wider aperture, and it lets you actually get everything in focus when even the smallest apertures just aren’t capable as when shooting close-up. the important thing here is to try it yourself. Try to get everything in focus with a small aperture, and then try the focus stacking methods. Do I use focus stacking everytime I shoot? Heck, no. But when I need to I do.

Here’s the previous article on focus stacking.

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