Depth of Field - Infinity???

[realworld]

Hey-- I keep reading about your depth of field being infinity...what does that mean? :mad2:

[Norfindel]

When you focus a lens at 10m, not only the objects exactly at 10m shows shap, objects closer and more distant also shows sharp, this is what one calls Depth of Field, the area that shows sharp.
If you focus the lens on certain distance, the far end of the Depth of Field lays at infinity, this is called the hyperfocal distance.
But "infinite depht of field" sounds strange, where do you saw that? To me that would mean everything from the very lens to infinity in focus, and i think that's a little impossible... I think you can get very close to that with a fisheye, however.

[mwfanelli]

When you focus a lens at 10m, not only the objects exactly at 10m shows shap, objects closer and more distant also shows sharp, this is what one calls Depth of Field, the area that shows sharp.
If you focus the lens on certain distance, the far end of the Depth of Field lays at infinity, this is called the hyperfocal distance.
But "infinite depht of field" sounds strange, where do you saw that? To me that would mean everything from the very lens to infinity in focus, and i think that's a little impossible... I think you can get very close to that with a fisheye, however.

After a certain distance, depth perception fails and everything looks as if it actually is at one distance. That's "infinity." FWIW, this is also why stars all look as if they are the same distance away!

[another view]

In practice, the shorter the focal length (wider the lens), the greater the depth of field (DOF). The science of it may be different, but in real world picture taking scenarios this is the case.

One thing to know about DOF is that it's based on "acceptable" sharpness, not an absolute. Realize that what's acceptable to me and what's acceptable to you (for example) might be different, and it can also make a difference in what the end result of the image will be. If you're trying to make a huge print, then figuring out the DOF and having everything that needs to be sharp fall just inside the DOF might not be good enough and you may want a bit more just to be sure that what needs to be sharp is acceptably sharp. Something on the edge of the DOF that's acceptably sharp in a 4x6 print may not be sharp with a 30x40 print.

Maybe you're hearing about focusing your lens to infinity? Or the DOF is from (for example) 8' to infinity?

[Broncosaurus]

I've read a few discussions of hyperfocal distance various web sites that were so poorly written that I don't think they understand it at all. It would certainly confuse anybody who hasn't used lenses with a DOF scale and an aperature ring on them. Some of them give the impression that at an exact aperature and focus combination, the DOF suddenly extends to infinity.
What goes on with any lens is that depth of field of a shot increases as you step down the aperature setting (go higher numerically). If you are focused far enough out, the far edge of your DOF (as indicated by the DOF scale) will line up with the infinity mark on your focus ring. That is the hyperfocal point. You can still focus farther away, the infinity mark will still be within the indicated DOF, so it's still hyperfocal. There's no strange optical effect going on. I hope this is clear. It's really simple if you have an older lens to look at.