We can learn much from our mistakes, so I think it’s very important to acknowledge them. Today we take a look at a situation where autofocus can fail us. Autofocus works best when there is some obvious contrast it can latch onto. It can struggle when you have a busy background, especially with a subject that blends into the background.
Today’s scene is of some trees and fall foliage along the edges of a marsh. I was immediately drawn to the lighter colored bare trees in the middle that, to me, stood out nicely against the colors of the foliage in the background and the darker brush in the foreground. However, my autofocus system with whatever settings I had, chose to latch onto the background trees with the colorful foliage, leaving the main focus, those white trees, slightly out of focus. I like the composition and I like how it looks when viewed small. But when you zoom in or attempt to print this large enough the focus issue becomes far more apparent.
Mistakes I Made
So, what did I do wrong?
To set the scene, I was shooting with my 200-400mm lens, a heavy and bulky lens. This lens is long enough it can be prone to vibrations when shooting with too slow a shutter speed. Additionally, I didn’t want a lot of movement in the trees and leaves. To keep the shutter speed from dropping too low I ended up using a larger aperture than I’d perhaps have preferred, at f/5.6. The trees weren’t all that far apart, but at 200mm f/5.6 can be shallower than you think. But I was ok with the colorful trees in the background being a little out of focus provided I could capture the lighter colored foreground trees in focus. In fact, that might even make them pop out a little more against the background. Granted, if I’d had a wider angle lens I’d likely have used a smaller aperture. But you work with what you have.
Speaking of working with what you have, at 200mm I couldn’t capture what I wanted of the scene. So I chose to create a stitched panorama and shot a sequence of 9 images in a 3x3 grid to capture the entire scene I was interested in. Here’s where one of my mistakes came in, though in the end it was a minor one. When shooting panoramas it’s best to find the appropriate exposure settings for the overall scene and then shoot in manual exposure mode so it doesn’t change from shot to shot. I forgot to do this. I was shooting in Aperture Priority mode which kept the aperture fixed at f/5.6. But the shutter speed varied from 1/200 to 1/500 second. Thankfully, the software does a good job of equalizing and blending exposures when you make the mistake I did.
The biggest mistake I made was blindly trusting my autofocus. I should have known that a busy scene like this had risks. I should have looked closely at the scene on the LCD, zooming in to verify the focus was where I wanted it. But I didn’t. I picked a tree, hit the autofocus button, locked in that focus, then shot the pano. As mentioned, the autofocus latched onto the colorful trees in the background and not on the foreground trees I wanted in focus. I’ve included a zoomed in closeup that might let you better see this. On a small screen you may never know my focus was off, but view on a large enough screen, or on paper, and it stands out.
