Depth of field and reflection

[Canon01]

Hi, Im new to the site, which is great btw, I see i Have lots to read and learn.

I read up here about DOF, What Im not really understanding is the following

Say object of focus is a flat glass pane, for example, to the right of me, making the left side out of focus.

does this glass then reflect out of focus as well? or not?

[herbert]

Hi Canon01,

Welcome to the forum.

The short answer is yes, the reflection can be out of focus even if the mirror is in the depth of field. This is because the reflected object is outside the depth of field.

The depth of field is a region around the focus point where objects appear sharp. Imagine looking along an skewer that passes through one slice of bread, an apple, then another slice of bread. The apple is the focal point. The two slices of bread determine the depth of field boundaries.

Note that the boundaries stretch as far as you can see to the left, right, up and down. All objects in front of the near boundary and behind the far boundary will be out of focus. This is true for light that has travelled directly to the lens or from a reflection.

So for your reflected image you need to think about where the depth of field would be in relation to the objects you see. Try it by photographing an object in a mirror straight on and then vary the angle between the mirror, you and the object.

But don't think too hard about it. Trust your eyes instead. If it looks out of focus, it is.

Alex