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Re: [OM] lens and film contrast

Subject: Re: [OM] lens and film contrast
From: "Tom Trottier" <Tom@xxxxxxxxxxxxx>
Date: Mon, 10 Jun 2002 02:23:21 -0400
On Monday, June 10, 2002 at 1:05, John A. Lind 
<olympus@xxxxxxxxxxxxxxx>
wrote re "Re: [OM] lens and film contrast" saying:

> At 14:20 6/9/02, Tom Trottier wrote:
...
> >The only advantage of a soft lens is that the depth of focus may be
> >increased.
> 
> This is incorrect.  Contrast and resolving power are two different
> things.  In an MTF graph, contrast is the y-axis and resolving power
> is the x-axis.  Indeed, in lens design the pursuit of both to extremes
> ultimately results in a trade-off.  Create too much of one and it
> bites into the other.  Various contributors to the effect are
> practical lens design aberrations which affect imagery most at wide
> open apertures and diffraction limiting which affects imagery most at
> narrow apertures.

If the lens has chromatic aberration, different colours of light will 
focus at different distances. This will lead to greater depth of 
field as the sharper image will come through the softer one.

Tom
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