Re: Antw: [Leica] Autofocus & Leica- Reason For Rom

[Lucien <lucien@ubi.edu>]

Robert,

I don't think the camera will check the aperture when fired.
It's not an Olympus.
That's why the R8 need to know before release 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 guess a little bit.
;-)

Leica said 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 it will be longer than with a 50/2.
This may be even more important with a motor.  :-(
ROM are passive, not active as far as I know. 
They don't calculate anything. It's the camera which will calculate
with the info stored at the factory inside the ROM.
With lenses without ROM, the camera will choose the longer delay.

Now, will you see any difference on you picts ?
With slides at the Olympic Games maybe.
;-)

Lucien

"Robert G. Stevens" wrote:

> As for Rom being used to tell the camera the true aperture of the lens, 
> the camera does this anyways since it meters through the lens.  
> It may just be a poor translation that you have read, 
> which should have read that it transmits
> the effective taking aperture.

> I checked my R8 manual and all it says is that the ROM lenses allow
> electronical exposure compensation.  I will see if I can find where I got
> the idea that the ROM transmitted the aperture value at time of release to
> the camera so that it can compensate for any mechanical errors.  This may
> be what Leica means by electronical, electro and mechanical.  This system
> is needed on motor driven cameras to ensure the aperture stops down fast
> enough and if it doesn't, to correct the exposure.