# Can a point source be located more accurately out-of-focus or in-focus?

Let's say I am taking a picture, and I know a priori that the image is of a single ideal point source of light at infinity.

With a perfect imaging system in focus, the image shows an Airy disk. I already knew to expect an Airy disk, so I can do some mathematical fitting to guess the center of the Airy disk. That's my best guess for the source location.

Alternatively, the imaging system might be somewhat out of focus. The image would show a much bigger blurry circle. Again, I can do some mathematical fitting to guess the center of the blurry circle. Again, that's my best guess for the source location.

My question is: Which approach would give me more accurate information about the location of the point source?

I can't see an obvious answer. In the out-of-focus image, you are drawing useful information from a much greater number of pixels, which is usually helpful in mathematical fitting. (Particularly if a large pixel size limits the resolution.) On the other hand, we normally say that defocusing an image simply erases its small-scale information, and I've never heard of anyone defocusing an imaging system on purpose like that!