Re: [Leica] Coatings and stuff -- smoke and mirrors

[Stephen Gandy <Stephen@CameraQuest.com>]

nice smoke and mirrors job,  Erwin.

When asked to provide specific data to support your assertions, you instead
provide generalized statements which may or may  not be true, but do not back
your assertions.

I spend a lot of time doing research for my site, and though of course I am well
capable of making errors, my site statements which you took exception to about
the 40/2 CL lenses not being multicoated, and the fact that the 40/2 CLE lens
may have had a change of optical design, were well researched.   My policy has
always been to correct any errors once better information has been available,
and I will if you can provide credible evidence beyond your opinion to the
contrary.

I ask you again,  refer me to the Leica publication which states these lenses
were multicoated.  Likewise, refer me to the Minolta publication which states
the 40/2 CLE lens was identical to the earlier 40/2 CL lens.  If you can't, it
seems your statements on these subjects are without merit.

I welcome your opinions, but when you claim something is factual, you should be
able to back up that claim.

Stephen Gandy


Erwin Puts wrote:

> When evaluating lenses and/or discussing optical properties or develoments,
> some background knowledge is most certainly necessary. Otherwise it might be
> the case that attention is drawn to the wrong aspects or even
> characteristics are mentioned as discriminative in a negative or positive
> way do not  have the  relevance or importance attributed to it. The Rokkor
> topic does bring home this observation with some force. The study of lens
> drawings is a case in point. Without knowledge of optical design, without
> knowing the optical specs of a particular lens, the comparison of two
> diagrams is very dangerous and most certainly will lead to misleading
> conclusions. Two identical diagrams can deliver significantly different
> performance and two digarmas that look different, might give comparable
> performance. The assumption that the diagram reflects optical quality is
> erroneous. If an optical designer is presented with whatever lens diagram
> and you would ask him/her to make any statement about performance or even
> assess differences, he/she would politely note that this is impossible
> without having access to much more important info. The noted difference of
> the third lens element between the Rokkor-CLE and the Summicron/Rokkor-C is
> obvious, assuming that the drawings are faithful. A Double Gauss lens is
> however, remarkably insensitive to small changes in glass thickness and
> without having any idea of the true radius of the glass and its type and the
> tracing of the rays,

> any conclusion, however tentatively, about design
> changes pointing to possible improvements, is a shot in the dark and because
> not based on analysis, inherently misleading.

Does this mean you shouldn't be making statements about lens design  without
having the correct information and analysis to back it up ??    Again Erwin, you
are begging the question.  Support your statement,  show me where Minolta states
the 40/2 CL and CLE lenses are the same optically.

> The only statement that can be
> corroborated is this: on the assumption that the diagramas are faithful, we
> note a difference in thickness of the third element, the purpose of which is
> unknown, without additional info.
> Coating is a second topic that is easily mis-interpretated.

Erwin, this little blurb has nothing to do with your assertion.  I didn't asked
for a discussion on coatings.  I asked you to show me the Leica publication
which states the 40/2 CL lenses were multicoated.  Where is it ??

> Single coating
> is an obvious technique, as is multiple layer coating: in the first case a
> lens surface is coated with one layer of a certain and in the second
> technique,  several layers are deposited, from two to nine and even more per
> surface. ML-coating is not in itself better than SL-coating, it depends on
> the design, on the glass types used and more. As example, when using high
> refractive glass, a SL-coating is more efficient than a ML-coating. If the
> Summicron were SL-coated, but used high RI glass, the effect might bettetr
> than a Minolta lens with ML and low refractive glass. ML-coating is often
> also used as a means to correct the colour transmission of a lens, again
> depending on the glass used. Leitz used three layer coating on selected
> surfaces of some lenses already in 1957, but did not mention it
> specifically, as they gave this aspect no public relation relevance. So if
> Leitz notes of a lens that it has coating, the inference that this has to
> imply SL-coating  is incorrect and even  if a certain lens does have single
> coating, that is not a sure sign of inferior performance.
> The idea that MC-coating is more effective in flare reduction and repression
> of secondary images as SL-coating, is not true either as a general
> statement. And the claim of a Lugger that the Summicron-C must be a
> SL-coated lens, as his Summicron-C does have a significantly higher flare
> level than the Rokkor-CLE, is quite rash. Read what Mr Crawley, of BJP fame
> noted about the Summicron-C: "the lens is flare-free at full aperture". If
> the Summicron-C, as claimed, is of SL-coating type and as claimed, the
> SL-type is of inherently higher flare level, such a remark were hard to
> accept.
> The type of coating is a lens characteristic that merits attention, but only
> in the context of the rest of the design parameters and without this
> knowledge, the singling out of coating properties as distinctive elements of
> the relative performance of a lens, is more reminiscent to a marketing act
> than enlighenment and advice for the user.
> Erwin