Re: [Leica] Rangefinder

[Dennis Painter <dpainter@bigfoot.com>]

imx wrote:
> 
> Someone remarked:
> "Sounds like you are saying that all Leica has to do is put in only
> 35/50/90 framelines, like the original M2 and the flare will be same as
> the M2.  I have my doubts but it would be an interesting product to
> test."
> 
> this quick comment is precisely the reason why I hesitated to discuss a
> topic of considerable engineering and optical complexity. THis is NOT what I
> said and this is NOT what can be inferred. Please for once read carefully
> and study and reflect a bit more.
> 
> Erwin

Erwin,

That someone was me.  If you read what I wrote I said "It sounds
like..."  but I think your statement that "NOT what can be inferred." is
wrong. It can easily be inferred. 

Going back and reading your post again and my impression is that you
never really addressed the issue of the difference in flare between the
M2 and M6. You do dance ever so closely to the topic but in the end
don't really address it. In short a nice post but it said nothing about
the issue of differences between the M2 and M6 finder which cause the M6
to have more flare (probably best described as white-out)

Now the M3 finder is vastly different than the M2 finder. I know this.
Why cannot Leica build the M2 finder again? Maybe if they did they would
learn about what causes the white-out.

Not wishing to be considered to quote you out of context I show my work
on how this is inferred by my comments inserted in your work.

Dennis



imxputs wrote:
> 
> Rangefinder topics.
> 
> I have hesitated for a long time to discuss the topic of rangefinder flare and
> accuracy. It is a theme that deserves some close reading and open mind
> approach. Let me start by noting that the rangefinder mechanism is extremely
> complicated as an optical and engineering construct. And without a firm grasp
> on its inner working, it is easy  to draw inferences that seem plausible, but
> are not.
> The M3 finder is different from all other M-finders including the M2. The
> difference is not so much the outward specs (magnification and number of
> framelines), but the internal design. The M3 has been designed as a 50mm
> finder at maximum and the optical construction is such that the ray paths of
> the finder entrance window, the rangefinder patch and the illumination window
> for the frame lines all follow a separate path. This design is optimised and
> fully dedicated for its limited task: have a 50mm view, with a permanent frame
> line for the 50 and the additional, but separate frames for 90 and 135.
> With the M2, a completely different design was necessary. The accomodation of
> the 35mm frame could not be squeezed into the optical and engineering
> parameters of the M3 construct and so the designers had to produce a different
> solution. Internally the M3 and M2 are totally different! To get the larger
> angle of view a smaller magnification was needed, and the impact this
> requirement had on the design it can hardly be understood. The permanent 50
> frame disappeared, and the finder, spot and illumination rays through the
> system followed a more complicated path. This path is partly the cause of the
> flare problem. Inherently the M2/4/5 finders are of the same design and share
> the same properties as the M4P and M6 finders.

{I take the following sentence to mean you are comparing the M4P finder
to the M2 finder. But it is vague and possibly that is the source of my
misunderstanding. Perhaps you are comparing the M4P finder to the M3
finder, with regard to "flare", if that was your meaning a direct
statement would be preferable.}

> Still is is evident that the
> M4P and later finders have a higher sensitivity to flare in the rangefinder
> spot. The addition of the 28 frameline and the pairwise display of two frames
> at once necessitated another change of the mechanism. The mechanism of
> framemasking had to be changed and compared to previous finders the clarity
> and transparacy of the finder was enhanced. Any M4P and M6 has brighter
> framelines and higher transmission than the previous models. Both requirements
> could be met, but the internal meachnism had to be changed. During this
> process, the enigmatic condensor was dropped, not because of cost cutting to
> save the company as one observer has proposed, but becuase it had no longer
> any functional value.

{and the following sentence seem to say that Leica should build the M2
finder to alleviate this "flare" problem, unless in some convoluted way
you are saying they all flare alike, if that is what you are saying,
just say it. }

> The tendency to flare under some conditions is a characteristic of the M4P and
> all M6 finders, but it is not absent from the M2/4/5 finders. It is however
> less pronounced and it is indeed almost absent in the M3 finder which is based
> on a different optical/mechanical construct.
> Some observers persist in stating that this state of affairs is due to
> costcutting and cheapening of the finder. It is not. 

{since you brought it up "brighter finder" I would like to know how you
measure this? My comparison of the M2 and M6 is that the M2 is the
brighter.  A spot meter pointed through the finder, each camera aimed at
the same illuminated surface? When you say the words "the price to pay
for.... more framelines.... is this propensity to flare." make it easy
to infer that removal of framelines would alleviate the flare.}

>The current M6 finder is
> as complicated and costly as an M4 finder (as example). The parameters however
> are different and the price to pay for the possibility of several
> magnifications, more framelines, brighter finder and more clearly delineated
> rangefinder spot is this propensity to flare. One may argue that this is a
> high price and that would make sense. I am sure Leica designers are aware of
> the trade-offs and will not rest until a solution may be found eventually. The
> changes of the rangefinder construct during its lifetime from M3 to M6 0.58
> can be documented (I have an article in preparation for this topic) and I will
> argue that these changes are made to accomodate the additional requirements
> and not to cheapen the mechanism to save a few bucks. Such a conclusion is
> embarrasingly devoid of factual knowledge of the optical and engineering
> paramters..
> I will also argue that the current requirements (more functionality and less
> propensity to flare) can not yet be solved as it is a equation with too many
> unknowns. If any one knows about the stubborn resistance of the intricacies of
> rangefinder mechanism to all these demands, it are the designers themselves.
> Not to have a solution is not equal to not working on one.
> Compare the Hexar with the new 0.58 finder and you see that the designers of
> both companies had to make decisions. The Hexar has a  dimmer finder with less
> visibility of framelines and less propensity to flare. The M 0.58 has a very
> bright finder, excellent clarity of the rangefinder spot and clearly defined
> framelines and still somewhat more flare sensitivity, but less than the 0.72.
> Evidently none can square the circle as yet.
> Another topic is the accuracy of the 0.58 finder. My updated website has new
> computations for the 0.58 and I can tell you that the 0.58 can be used with
> full confidence with the 1.4/50 and the 1/50 and the 2.8/90 and with good
> confidence with the 1.4/75 and 2/90. Of course when all conditions are in the
> negative,the 2/90 will be on the limit. But there is no calculation or
> practical experience that precludes the use of the 2/90 and all the others on
> a 0.58. In my view the 0.58 might be bringing the 0.72 to a marginal role.
> Please note that this text is part of an upcoming article and so is
> copyrighted and please when using part of this text, do not forget to quote
> and cite the origin.
> Erwin