The question was recently asked: Can one see an object, (sharply), at
infinity, at the same time as they are focusing on a finger at a
distance of, only,.
18 inches ?

I say the answer is NO.

If the eye is focused at infinity, the DoF ranges from infinity back to
about 4 feet.

If the eye is focused at 18 inches, the DoF covers a range of from
about 14 inches, out to about 25 inches, not out to infinity, as was
inferred.

The human eye is similar to an auto-focus lens, it can only auto-focus
on specific objects, not between objects as a manual focus lens is able
to do.


Best regards,

DON

Don Lopp wrote:

> The question was recently asked: Can one see an object, (sharply), at
> infinity, at the same time as they are focusing on a finger at a
> distance of, only,.
> 18 inches ?
>
> I say the answer is NO.
>
>

I think this is correct. However in terms of this observation being
"useful" in
terms of application to 3D photography, I'm not certain. This is because
one will likely *think* one can see both the finger and the distance
simultaneously
even if one can't really. The perception may be more important than the
fact.

Mike K.

Hi Mike:

You are probably correct. The main reason that i believe that I am
correct, is that if one focuses at 1 1/2 feet, the DoF is very shallow.

The DoF is about 12 inches, (1 foot to about 2 feet), at f/11, which is
about as far down that the eyes stop down. If the eye were able to
be focused at 3 feet, or 5 ft, the DoF would be much larger, but the eye
is on auto- focus, so 3 ft or 5 ft is not an option.


Best regards,

DON