[rollei_list] Re: Contrast and Resolution
- From: "Neil Gould" <neil@xxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sat, 10 Nov 2007 10:16:25 -0600
Hi Eric,
> Date: Fri, 9 Nov 2007 09:47:25 -0500
> From: "Eric Goldstein" <egoldste@xxxxxxxxx>
> Subject: [rollei_list] Re: Contrast and Resolution
>
> Neil -
>
> As you are familiar with shooting a test chart, a thought experiment
> may prove helpful...
>
> Imagine examining the negative of a test lens where the test chart's
> hard contrast of black and white lines is reduced to gray and white
> lines by the lens. Still, each line (to the limit of lens and film) is
> recorded, but the contrast is reduced. The contrast can be
> significantly reduced (50%, 75%, more) and still the eye can record
> the detail...
>
This is exactly how I interpret the process... noting that the eye can
record the detail only until the contrast drops too low to do so, in other
words there is an inexorable relationship between the two. What I'm trying
to get a grip on are the comments that suggest that the two are
independed, much less whether the relationship is direct or inverse.
> Further, think about the effects of apodization on the lens (detailed
> in a previous post)...
>
Yes, I'm still trying to understand that process, as it seems one step
removed from the question at hand.
>From Wikipedia:
"[...] Generally, apodization reduces the resolution of an optical image;
however, because it reduces diffraction edge effects, it can actually
enhance certain small details. "
Is the process is increasing resolution by adjusting the contrast?
> Are the edges of the smallest of the visible
> test chart lines darker along the edges or in the center? Further
> thought along these lines in this experiment might lead to an insight
> of why light energy drawn in the center of the points would lead to a
> greater number of smaller lines being recognizable than light energy
> drawn on the edges of the points...
>
The way I'm currently understanding this has to do with refocusing the
signal reinforcement (beat frequencies) resulting from aperture size. Not
being a lens designer, my notion is that coatings affect this by filtering
out the lower amplitude signals. It is logical that, however it's done,
light energy drawn to the cernter of points would lead to higher resolving
power by increasing contrast. So, as it doesn't isolate contrast from
resolution, I'm still at a loss to grasp such a notion as the two being
unrelated.
Regards,
Neil
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