[Leica] Re: Autofocus

[lrzeitlin at optonline.net (Lawrence Zeitlin)]

On Apr 25, 2007, at 11:15 AM, A. Lal wrote:

> On SLRs AF works at full aperture. It cannot compensate for focus  
> shift when
> the lens is stopped down to working aperture.  The Contax AX uses  
> the moving
> film plane to focus the lens wide open, not to compensate for focus  
> shift
> when stopped down..
>
> On  RF cameras, if the AF is designed to work through the lens at  
> working
> aperture, the lens' DOF will compromise AF accuracy. This is why  
> the G2 and
> many P&S cameras  used an external AF system.
>
> The only way to compensate for focus shift when the lens is stopped  
> down is
> if the AF sysem is supported by a look-up table built into the  
> camera with
> data for each lens.


I think you've got it!

The future Leica M  should have autofocus at working aperture using a  
moving sensor plane and a chip with a lookup table for all Leica  
coded lenses. This would insure a ready influx of cash since all  
Leica users would ante up $125 to have six dots placed on their  
lenses. Imagine the profit margin.

Also the look up table would have to be periodically revised as new  
lenses are added. Another cash cow. A new chip costs about $3 but the  
company could charge $300 for the revision. If this were done, the  
company wouldn't even have to assure focus constancy on its lenses.  
Forget about precision machining of the camera rangefinder linkage. A  
correction factor for each camera could be loaded on to the chip at  
manufacture. After all, Leica used thin metal shims under the lens  
flange to adjust flange to film distance years ago. And you thought  
the old Leicas were precision machines.

Leica could be on the verge of turning a profit with the M digital.  
As an example, I own a chart plotter for my boat. This chart plotter  
takes the GPS reading and shows me my position on a navigation chart  
imaged on a 8" x 10" LCD display. The charts are digitized versions  
of the NOAA charts already paid for by taxpayer money. They are  
encoded on a chip, artfully designed to fit only my specific chart  
plotter. Do I get the charts for free? You've got to be kidding. Each  
chip costs me several hundred dollars for about 300 miles of  
coastline. A charted trip along the Atlantic coast from Maine to  
Florida would cost about $1600. As you have probably guessed, each  
chart revision costs the same. The reprinting and repackaging of free  
government navigational information has kept several companies larger  
than Leica alive for years.

Larry Z