[rollei_list] Re: Contrast and Resolution
- From: Jerry Friedman <tinycameraco@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sat, 10 Nov 2007 08:17:05 -0800 (PST)
Neil
Perhaps it would help if you recalled the astigmatism test
you had at your optician. You were shown two crossing
lines, of equal resolution but differing in terms of
contrast. As the lenses, and their rotation, put before
each eye changed, the lines looked increasingly different
--not in terms of actual resolution-- but in terms of
relative contrast. This is probably the best example I can
think of illustrating how clarity of image might be the
same (resolution) while they still might appear vastly
different to the eye.
In my case, I have found that Zeiss lenses produce "better
images" which, for me, means greater contrast. Hence, my
fondness for some Tessars. Tessars may have poorer
resolution in the corners, but, for me, the increased
contrast at the center more than carries the load.
Jerry Friedman
--- Neil Gould <neil@xxxxxxxxxxx> wrote:
> 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
>
> ---
> Rollei List
>
> - Post to rollei_list@xxxxxxxxxxxxx
>
> - Subscribe at rollei_list-request@xxxxxxxxxxxxx with
> 'subscribe'
> in the subject field OR by logging into www.freelists.org
>
> - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
> 'unsubscribe' in the subject field OR by logging into
> www.freelists.org
>
> - Online, searchable archives are available at
> //www.freelists.org/archives/rollei_list
>
>
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
---
Rollei List
- Post to rollei_list@xxxxxxxxxxxxx
- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe'
in the subject field OR by logging into www.freelists.org
- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
'unsubscribe' in the subject field OR by logging into www.freelists.org
- Online, searchable archives are available at
//www.freelists.org/archives/rollei_list
Other related posts:
