RE: Digital negative novice needs help.

Richard - Ctein's writings may not be scientific papers but they seem
generally rigorous to me, well above the average darkroom book. He
may have sometimes reached erroneous conclusions, but even in those
instances his reasoning was good reading.

Also, there are some facts. Ektaflex prints known to resolve 20 lp/mm
are visibly less sharp to the eye that other types of RA4 paper prints
resolving 65 lp/mm. How do you explain this if 10 lp/mm is the resolution
limit of the eye?

I think that your statement "increased resolution does
not necessarily mean the edge contrast is greater", while correct,
is misleading. I doubt that in practice you will be able to produce
high acutance, low resolution prints. If the resolution is low, then the
edge sharpness will not be satisfactory to the eye, and I think that's
what Ctein was saying.

gregory

> -----Original Message-----
> From: Richard Knoppow [mailto:dickburk@ix.netcom.com]
> Sent: Friday, April 21, 2006 6:34 PM
> To: alt-photo-process-l@usask.ca
> Subject: Re: Digital negative novice needs help.
>
>
>
> ----- Original Message -----
> From: "Gregory Popovitch" <greg@gpy.com>
> To: <alt-photo-process-l@usask.ca>
> Sent: Friday, April 21, 2006 6:35 AM
> Subject: RE: Digital negative novice needs help.
>
>
> > Ctein's excellent book Post Exposure has a chapter talking
> > about this.
> > He does say that even though the eye may not resolve more
> > than 10 lp/mm,
> > it can clearly see a difference betwenn a print resolving
> > 20 lp/mm and
> > one resolving 60 lp/mm. He says that it is because human
> > vision doesn't
> > just resolve fine detail, it selects for and analyses edge
> > detail. The
> > human eye can see whether edges are blurry even in the
> > finest
> > observable detail.
> >
> > The conclusion is that a print has to resolve at least 30
> > lp/mm for
> > "perfect" sharpness (that's probably not quite applicable
> > to matte prints
> > on textured papers).
> >
> > gregory
> >
> I am not sure this is true. The visual system does judge
> sharpness from edge contrast but increased resolution does
> not necessaryly mean the edge contrast is greater. The
> "acutance" effect in film is an example. Acutance is a
> measure of perceived sharpness. In film it is increased by
> exagerating edge/border effects. The result is an increase
> in edge sharpness but often a reduction in actual resolution
> because of the distortion at the edges.
> Ctein has a lot of good stuff in his writings but also
> shows a lamentable lack of rigor and willingness to
> extrapolate from the known to the imaginary.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@ix.netcom.com
>
>
Received on Fri Apr 21 19:21:41 2006