RE: [Leica] sharpness & optical quality

["Dan Honemann" <ddh@home.com>]

All well and good, Erwin, but which lens is _better_?
:) :)

> -----Original Message-----
> From: owner-leica-users@mejac.palo-alto.ca.us
> [mailto:owner-leica-users@mejac.palo-alto.ca.us]On Behalf Of Erwin Puts
> Sent: Friday, April 28, 2000 8:02 AM
> To: leica-users@mejac.palo-alto.ca.us
> Subject: [Leica] sharpness & optical quality
>
>
> >  In other words: sharpness is NOT everything
> >  in photography. What about "residual" tonal gradation,
> >  shadow detail, highlights' subtlety, color accuracy when its acutance /
> >  edge resolution goes down somewhat at f/2.8 or f/2 ?
>
> >Right on. When will people realise this? Most modern lenses are 'sharp'
> >enough. The occasional massive step forward in resolution (35
> lux -> 35 lux
> >asph) excepted. The character resides in the rest of their qualities. Add
> >bokeh to the above list, for a start. Judging a lens by its sharpness is
> >like judging a car by the size of its engine.
>
> These comments can be read and heard often. They are not
> representative of current thinking about image quality and
> demonstrate an embarrassing lack of insight in the true nature of the
> topics discussed.
> I cannot think of any person or book discussing optical quality in a
> serious way who will uphold the notion that "sharpness" has relevance
> to image quality. Sharpness is often equated with resolution, which
> is not the case. No one has ever been able to define 'sharpness' in a
> consistent or measurable way. Fact is that "sharpness" does not
> exist. The notion of sharpness impression does exist, but that is a
> psychological phenomenon, loosely related to acutance. Resolution
> only refers to the ability to distinguish between two adjacent
> objects, the smaller the distance between two objects, the higher the
> resolution. It has no direct relation to image quality, but PopPhoto
> still uses it as a criterion for optical performance. The measurement
> of resolution is so dependent on so many uncontrollable parameters,
> that no one would propose resolution as a discriminating
> characteristic for optical systems. The suggestion that the Summilux
> asph has a much higher resolution value than the previous version is
> not true. Contrast is higher, but not resolution, which is only
> marginally improved due to the higher contrast.
> It is remarkable that the sharpness topic is discussed often by
> persons  who  wish to denounce the value of the concept, while most
> persons who discuss optical quality do not even think of using this
> concept.
> Now bokeh, which is just a new word for the older concept of
> 'rendition of unsharpness areas' is a very imprecise notion and is
> based on perception and personal judgment and appreciation. The
> sharpness impression is also imprecise and based on perception etc.
> So if one argues in favour of bokeh or highlights' subtlety or
> residual tonal gradation (whatever that may be) or any other
> impressionistic criterion, we are not proposing anything new. I do
> not see the added value in replacing the vague and obsolete notion of
> sharpness with another concept just as vague and unreliably related
> to the real optical quality of a lens.
> A lens cannot be characterized by one simple criterion, measurable or
> not. And the definition and assessment of the optical quality  of a
> lens is a major undertaking that defies any attempt to simplification.
> Indeed a lens has a character, just like an individual, but we are
> all aware that the description of a person's character is a highly
> subjective and dangerous activity. So is the description of the
> character of a lens.
> The recent discussion about the perceived differences between the
> Nokton and Summilux 50 clearly demonstrates the pitfalls. The Nokton
> lens was not allowed to show its qualities in that approach.
> When proposing characteristics for evaluation of a lens, we should be
> aware that this area of discourse can be studied from several
> perspectives and levels. Any  photographer can choose whatever lens
> (s)he wants, based on whatever  arguments. A discussion of these
> choices  may be enlightening as we get a glimpse into a
> photographers' personal decision chain. This is however no substitute
> for a comprehensive assessment of the optical quality of a lens,
> based on current thinking and theory of image quality.
>
>
> Erwin
>
>