[Leica] Usefulness of ROM, was: R8 or R7

[Lucien <director@ubi.edu>]

John Collier wrote:
> 
> Right now ROM is only "useful" if you have an automatic zoom head on your
> flash. Personally, I would not bother with the conversion.

John,

With ROM,  the R8 will know before firing what will be the
real aperture (including vignetting which is different at
each aperture and on each lens) in order to calculate more
precisely the exposition.
With lenses without ROM the camera will give an average result.

Leica said also that small lenses with ROM permit shorter
time parallax than bigger because, thanks to the ROM, the
camera knows the exact delay before the diaphragm is closed
and can start earlier the process of firing.
With a 280/2,8 at f8 it will be longer than with a 19/2,8 at
same aperture, or than with the same 280/2,8 at f2,8.
With lenses without ROM, the camera will always choose the
longest delay.

With the APO-Extender 2X ROM (#11 269) the viewfinder will
display the real aperture if used with a ROM lens, and the
camera will know the new focal length of the lens (or zoom)
and move the flash head accordingly.

By the way, ROM are passive.  They don't calculate anything. 
It's the camera which will calculate thanks the info stored
at the factory inside the ROM.
At the end of manufacture, or when retrofitting of older
lenses, every Leica-R lens is individually measured and
programmed in order to make sure that the potential accuracy
of the exposure metering is maintained at each aperture. Two
identical lenses may have different ROM's information inside.

If, after the lens left the factory, there is a problem in
the diaphragm mechanism, the ROM will NOT know it.
:-(

Now, is all this really useful ?

I asked for the modification for lenses that I use with the
APO-Extender 2X and/or flash.
And I'm happy with the results (less mistakes).

That's all I can say.

Lucien