[Leica] M8 upgrade - 90 Cron APO focusing problems now Question????

[leica at web-options.com (Bob W)]

I don't know, but perhaps it's something to do with chromatic aberration,
and the different ways in which film and sensors handle it. In general
lenses cannot focus all wavelengths of light at the same plane on a surface,
so a lot of effort in lens design goes into correcting for this, including
the use of such things as achromatic elements. Different lenses use
different ways of correcting for these aberrations. Film and digital sensors
have react to and handle light differently. The lenses were designed for
film, which probably masks some of the inaccuracies that remain in the lens.
This could explain why digital sensors respond differently to different
lenses.

Bob

> -----Original Message-----
> From: lug-bounces+leica=web-options.com@leica-users.org 
> [mailto:lug-bounces+leica=web-options.com@leica-users.org] On 
> Behalf Of Aram Langhans
> Sent: 13 December 2008 19:10
> To: lug@leica-users.org
> Subject: [Leica] M8 upgrade - 90 Cron APO focusing problems 
> now Question????
> 
> Question.  I am not an M user, but am curious.  How can this 
> be?  How can a
> lens focus properly on a film camera but not on the digital 
> M?  If this
> happened with every lens, I could understand that - something 
> out of whack
> with the camera.  But if other lenses that worked on a film 
> camera also work
> on the digital M, why would one lens behave this way?
> 
> Aram, the curious R user.
> 
> 
> 
> > Date: Sat, 13 Dec 2008 12:27:41 +0800
> > From: H&ECummer <cummer@netvigator.com>
> > Subject: [Leica] M8 upgrade - 90 Cron APO focusing problems
> > To: lug@leica-users.org
> > Message-ID: <AF2C207F-8441-4C80-B420-C5B3354292BD@netvigator.com>
> > Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
> > 
> > Hello Luggers,
> > I have been having a dialogue with Schmidt (the local Leica
> > distributor) about getting my 90mm Summicron APO to focus 
> properly on
> > my M8. Despite adjustments to the lens it still back 
> focuses wide open
> > in the close range.
> > Trying another tact I decided to go for the M8 upgrade to the
> > viewfinder, and that led in a cascade to the new shutter upgrade and
> > in a what the hell attitude I also opted for the scratch resistant
> > LCD. I now have the camera back and my 90 Cron is no better matched
> > than before the upgrade and adjustment. Lux lenses focus fine as
> > before.
> >  
> 
> No virus found in this outgoing message.
> Checked by AVG. 
> Version: 7.5.552 / Virus Database: 270.9.17/1846 - Release 
> Date: 12/12/2008
> 6:59 PM
>  
> 
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
> 
>