Then you should focus on something that will give you the best depth of field in those parts of the images you want in focus..

Nothing is enough for the man to whom nothing is enough...

Linslus wrote:.

If there's a subject in the frame, for example a person, I focus onthe person of course. But what if there's no obvious subject, likeI'm shooting a landscape with a big green field of grass and the bluesky and thats it, then what do I focus on?.

Typically the line between sky and field..

A member of the rabble in good standing..

Autofocus needs contrast to lock on to. The horizon (sky/ground contrast) should be OK. The lens will then focus on infinity, which is probably fine for the sorts of pictures you are describing. If you have a big area of low contrast that the autofocus cannot get a grip on (e.g. expanse of blue sky) just set focus to manual and set the lens to infinity..

If you're feeling really clever you can set the focus manually to the 'hyperfocal distance', a point in front of infinity which gives you the maximum possible depth of field extending from in front of the focus point to behind it (i.e. infinity). Of course this relies on you knowing what the hyperfocal distance is, which will depend on the focal length and f-stop.....

Best wishesMike..

This is often a good time to set the camera to manual focus, and then focus on something else, perhaps in some other direction, abotu the same distance fromyou as the middle of the scene..

If you, or the camera's autofocus system, doesn't focus on something, it may automatically set itself too close, and the field will be fuzzy, or too far away, and the foreground will be fuzzy..

BAK..

What does infinity mean? How do I focus on that?..

Http://en.wikipedia.org/wiki/Infinity_focus.

The symbol is like a figure 8 on it's side. You will find it on the lens at the other end of the focus scale from the closest focus distance..

Mike..

I wonder about the same thing, with a 17mm lens on a 30d..

I want foreground and infinity in focus although sometimes there is nothing after 3 feet to focus on within the picture..

Ive tried hyperfocal and i'm not happy with the far distance sharpness..