On Wed, 21 Feb 2007, J. C. O'Connell wrote:
> YOU are the one confused here. ALL autoaperture
> M42 lenses have "open-aperture auto aperture" (your
> term, not mine), that's
> what auto aperture ISs by defintion. The lens aperture
> stays open all the time during focus and composition
> and only stops down during the moment of exposure. It then
> reopens immediately and automatically after the
> exposure is made. The vast majority
> of M42 lenses are auto apeture models. Yes, there are/were
> some presets, some semi-automatics, and some manuals
> with regards to the aperture function but the vast
> majority of them (M42) are full auto-aperture.
>
> The reason I say you are confused is you are associating
> the metering directly with the autoaperture ( someone else was
> doing the same thing too, but its a mistake ) because the
> metering technique is independent of the auto aperture
> function. Most M42 bodies do stop down metering, but this
> is only temporary, during the metering function itself, and
> the lens goes back to normal autoaperture functioning
> once the proper meter reading is made ( if the body even
> has metering, or you choose to use it, or choose to
> take another meter reading).
>
> OPEN APERTURE METERING- which is what I think you
> are referrring to ( which is not the same thing as
> auto apeture), is where you can take meter readings
> without stopping down the lens. That is not as
> common as autoaperture, but it is not as needed
> or useful as autoaperture is either. All open aperture
> metering lenses have autoapeture function too, but
> not all autoaperture lenses have open aperture metering
> function. I am not advocating a dedicated M42 DSLR
> be produced for open aperture metering, I am advocating
> one to get the AUTOAPERTURE function, which most
> M42 lenses support, and which is sorely lacking when
> you mount M42 lenses on any current DSLR including
> Pentax's via a M42 mount adapter ring.
>
> jco
>
My confusion of terminology was primarily induced by your rabid
infatuation with auto-aperture M42 lenses. I figured you must have
*meant* open-aperture metering because that would be the main advantage of
such a body. Auto-aperture with automatic stop-down metering still has
the major problems of:
- Meter inaccuracy due to angle on incidence
- Meter inaccuracy due to falling off the end of metering range while
stopped down.
- Manual focus aids ineffective at apertures smaller than 5.6-8 or so.
- Sticky apertures (LOTS of 'em on these old suckers... still work fine
for manual stopdown metering, but not fast enough for auto)
Automatic aperture with stop-down metering does not address any of
these rather large problems. All it does is save one from having to flip
a switch between focusing and pressing the button. The meter will work
fine in 'P' mode once stopped down like that. Even more intuitive and
"automatic" then the GB kludge for K/M lenses.
-Cory
--
*************************************************************************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
*************************************************************************
--
PDML Pentax-Discuss Mail List
[email protected]
http://pdml.net/mailman/listinfo/pdml_pdml.net
