F/22… Ooops

Few years ago, I was shooting a landscape shot and out of ignorance I stopped down my aperture to f/22 thinking that I would get a sharper shot from front to back. That was what I remembered from my photography course and I thought that would be fitting for the shot. Then it happened, “Error 99” That is canon’s way of saying that your lens or something screwed up serious ly and you have to shut the camera off to be able to shoot again.

At first this happened in frequently as I rarely used f/22 but slowly the problem spread to anything above f/4. I had the lens fixed numerous times but in reality I should have fixed the root of the problem “Why the hell do I continue to shoot in f/22 when I know better?” The lens is now stuck and will not release from its position. Now this is a problem for a wide angle lens when you want to say shoot in f/8 where it is probably the sharpest. How do I know this, Dylan Goldby.

As I said before in my post about the radio show, I was put in my place about the issue. Now, this was some thing that I had known but never really thought about. However, when someone calls me on it, immediately the problem came clear. “Why were you shooting in f/22?” Dylan asked and I stumbled back with “Well… I… you know… wanted everything sharp in the frame… increase the depth of field…” and that was when the word “diffraction” came up and turned on the lights in my underused brain bringing up the glossary section of the horribly outdated camera text book from Lakehead University.

Basically, for those who don’t know what I am getting at, I will put it simply. At f/22 the aperture of your lens is at it’s smallest (for most some go smaller). Typically, parts of your photo will be sharper but not completely because of diffraction. Due to the small aperture, the light will diffract or “bend” when it passes through. This will cause parts to be a little fuzzy due to the diffraction. However, setting it to a midrange f-stop like f/8 will minimize the diffraction giving a sharper image.

The ideal settings will depend on the lens but normally the mid-range apertures like f/8 to f/11 will always give you a sharper overall image. Now I know that most seasoned photogs will scoff at this post but I felt that it was worth explaining because many people may not realize the intricacies of lens diffraction.

Some great resources can be found here at Luminous Landscape

In my quest to further understand lens diffraction I also found a great explanation at Cambridge in Colour that has a great interactive table that gives you a graphic idea of what I am talking about.

Lastly Ken Rockwell has a great tutorial on the topic of diffraction. And he points out one major concept:

Unless you absolutely need depth of field, avoid apertures smaller than f/8 on modern digital SLRs.

Which is what I should have been doing all along and that Dylan also said to me in the studio. Wow, now I know. Please take the time to read the above articles in full. They are a great read.