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Re: [OM] Question on Focus

Subject: Re: [OM] Question on Focus
From: dreammoose <dreammoose@xxxxxxxxx>
Date: Tue, 23 Apr 2002 01:25:40 -0700
In Dave Shupe's origianl question, he mentioned that the image seen through (one of?) the split image area(s) focused at a different point than the matte area, which was cousing him some trouble/confusion. Frieder's answer talked about the problem with aerial images and focusing, but didn't make the connection to the original question part about the image in the split screen area..

An aerial image is the image formed in space in the foacl plane of a positive lens. In the case of binoculars and telescopes, the eyepiece focuses on and magnifies this aerial image while the objective lens stays put. In a camera, the lens moves to focus the image on the film. In an SLR, the eyepeice is fixed and in most cases, has no focus adjustment (exceptions are OM-3 & 4 series). The only way to form an image that is always the exact same distance from the lens as the film is to insert a translucent 'screen' upon which the camera lens projects an image. The pentaprism and eyepiece lens(es) turn the image on this focusing screen to be correct reading left to right and at a comfortable apparent viewing distance, since nobody with normal vision can focus on something an inch away.

Richard F. Man wrote:

At 08:58 PM 4/22/2002 -0700, moose wrote:

That is why the image seen through the split image area is not useful for focusing except by it's displacement along the split. It is also an aerial image.
...



Can you clarify? I mean what other (incorrect) use is there for the split image area if not for the displacement along the split?

Also, what's an aerial image?



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