[Leica] 90mm APO Summicron M Asph Price Range

[richard at richardmanphoto.com (Richard Man)]

How does one measure the cam modifications needed?

I asked SK Grimes to add RF coupling to a 50 Summicron R for my XPan. It
focuses down to ~8 feet fine and then rapid lose it as it gets closer. I
would love to have someone mod the RF so that it's accurate down to, lets
say 3 feet.


On Thu, Feb 2, 2012 at 9:01 PM, Marty Deveney <benedenia at gmail.com> wrote:

> Hi Henning,
>
> Oh.  The 90AA I trialled showed quite a bit of focus shift when I
> measured it, but it could have been due to the kind of issue you've
> described here.  I didn't put it on an optical bench.
>
> Yes, I have a table I calculated for the 75 Summilux somewhere about
> how to proportionally compensate at each aperture where focus shift is
> an issue.  I never liked the 90AA enough to buy one so I never
> characterised this - thanks for making me aware of that - I'll be on
> the lookout for it.
>
> Thanks,
>
> Marty
>
>
>
>
>
> On Fri, Feb 3, 2012 at 12:41 PM, Henning Wulff <henningw at archiphoto.com>
> wrote:
> > Marty,
> >
> > This is not a focus shift issue as in - it shifts plane of focus as it
> is stopped down. This is an issue as in - it focusses accurately at one
> distance, but not at another, all at the same aperture. The 90AA exhibits
> very little focus shift, as stopping it down doesn't change the plane of
> focus much at all, at any distance.
> >
> > The problem with mine, and I believe Howard's, was that the cam did not
> follow the focus properly. If the lens focussed properly at infinity, it
> was off at 10m and then on again at 3m. Not very user friendly. I too now
> have some other 90 options which work better.
> >
> > In a related vein, the 75 Summilux exhibits focus shift in the
> traditional manner, but at f/2.8 it is off the intended focus plane by the
> same proportional amount at every distance, and I have learned to
> compensate. I can use it very well, and have a high degree of confidence in
> it.
> >
> > Henning
> >
> >
> >
> > On 2012-02-02, at 4:56 PM, Marty Deveney wrote:
> >
> >>> Another consideration about the 90 APO Summicron Asph is that some of
> them do not focus accurately on the M8 or, by extension, the M9.
> >>
> >> This is not an issue with "some" of them.  The 90AA has substantial
> >> focus shift - it's an atrefact of the design.  The lens gets
> >> calibrated for optimum focus at a specific aperture and object
> >> distance.  Focus shift means that even a properly calibrated lens will
> >> focus incorrectly at some apertures and object distances.  In a
> >> rangefinder camera, the mechanism assumes a linear focus arrangement,
> >> but this isn't the case and there is no engineering solution to make
> >> the cam shape change with aperture.
> >>
> >> This problem also occurs with SLRs because they focus wide open and
> >> then stop down before shooting without re-focusing.  In autofocus SLRs
> >> where there is lens-camera communication I've never understood why
> >> manufacturers didn't characterise the shift and make camera bodies
> >> that compensate for it, or have a menu selection that enables the
> >> camera to focus then stop down and re-focus then shoot.  The former
> >> may not exist because autofocus is less accurate than manufacturers
> >> like to admit, the latter might attract more complaints than praise
> >> because it would be slower.
> >>
> >> Marty
> >>
> >> _______________________________________________
> >> Leica Users Group.
> >> See http://leica-users.org/mailman/listinfo/lug for more information
> >>
> >
> >
> > Henning Wulff
> > henningw at archiphoto.com
> >
> >
> >
> >
> >
> > _______________________________________________
> > Leica Users Group.
> > See http://leica-users.org/mailman/listinfo/lug for more information
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
>



-- 
// richard <http://www.richardmanphoto.com>