Susan wrote: Not one of my favorites but brings up a question? How do you photograph kids on swings? Motion catch???
There are some pointers but no sure fire solution. Use a fast shutter speed. That would be to set the shutter at a fixed setting and let the ISO and f-stop adjust. I would use 1/500 to stop motion on a swing.
Manually focus as the subject moves. The motion is toward, away, or across your field of vision. Focus out or in depending on the direction of motion like the swing. For objects moving across the field of view – pan the camera. That is to say swing it in the direction of the motion. It will blur the background and focus on the object such as a car. No one much uses manual focus anymore. But it’s there if you want to try it.
Focus points are now in multiples on all advanced digital cameras. The Nikons and Canons offer a choice of metering patterns. There are multiple points of focus where the subject crossing that sensor point will cause the lens to focus on the subject. On the Nikon D200, I use the closest subject focus choice. It focuses reliably on the nearest subject, which usually happens to be my subject of interest. It works most of the time. This is what I rely upon as far as focus.
Anticipation is important. Most things we photograph are moving in a reasonably predictable pattern. Not so for wildlife but most things like a swing have predictable paths. You can focus on a point and let the action come into the field of view. You can pan the camera and follow the action. You can continuously focus and fire the shutter at the critical moment.
There is a button on Nikon and Canon cameras, which allows you to focus first and then trip the shutter separately instead of a single button that you depress partially and fire the shutter. This gives a bit more control. It is what the sports photographers rely upon. It’s a very good trick and feature on the camera. The manual takes a page or so to discuss it and I swear I skipped over that part until I shot tennis. Then it all made sense.
Finally be prepared to shoot a lot of images. There will usually be one or two that you will want to keep. The rest will be technically good but not outstanding.