Or try this...
Stand in front of a store window, and focus on whatever is in the window
display. Now re-focus on whatever is reflected in the window. You have to
focus closer to infinity, further away, even thought the window is closer to
you.
Piers
-----Original Message-----
From: owner-olympus@xxxxxxxxxxxxxxx [mailto:owner-olympus@xxxxxxxxxxxxxxx]
On Behalf Of John A. Lind
Sent: 13 July 2003 03:14
To: olympus@xxxxxxxxxxxxxxx
Subject: Re: [OM] Photography and Physics
Importance: High
At 09:16 PM 7/12/03, Boris asked:
--snip
>Does it mean that if there is a window and I want to focus on the
>subjects
>that the window reflects, the lens has to be set up at a distance equal of
>the distance between the window and the subject and not the distance
>between the lens and the window?
It must be set up for the sum of the two:
camera->window distance PLUS window->subject distance
The focus distance is the entire light path from subject/object to lens.
Confirm this with the following experiment. Stand about 10 feet in front
of a mirror with camera in hand and focus on the mirror (a mirror edge will
work). Look at the focus distance on the lens. Should be about 10 feet,
distance from camera to mirror. Now focus on yourself, or the camera in
your hands. Should be about 20 feet, the distance from you to the mirror
and plus distance from mirror to camera. Allow for a little error in the
lens markings; they're not always accurate to eight significant digits.
-- John
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