Infinity Focus


Today’s Question: When photographing a far-away subject such as the moon, if I manually set the focus on the lens to infinity will I be assured of proper focus?

Tim’s Quick Answer: Almost certainly not. Setting the focus to the greatest distance (ostensibly “infinity”) will not always ensure proper focus, even for a subject that is at a very great distance.

More Detail: In actual fact, I find that setting most lenses to infinity will definitely produce an image that does not have optimal focus. I’m sure the use of an infinity setting for focus works for some lenses in some situations, but I would absolutely not consider this a reliable technique.

Instead, for situations where autofocus doesn’t necessarily provide an ideal solution (such as with night photography) I recommend using manual focus in conjunction with the live view preview on the camera’s LCD display.

This approach obviously is best used in conjunction with a tripod. After framing up your scene, you can then use the zoom feature for the LCD display (not adjusting the zoom setting for the lens) to zoom in on a key area of the scene you are photographing. You can then manually adjust focus, with the autofocus turned off for the lens.

You’ll obviously want to use other techniques, such as employing a cable release, in order to help ensure optimal sharpness, especially if you are using a relatively long exposure time. But you will likely notice in these types of situations that when you adjust the focus manually with the assistance of the live view display, even for very distant subjects you are likely not ending up with the focus set at infinity. In many cases, in fact, you may be surprised at how far from the infinity setting you actually end up setting the focus.