Archived posting to the Leica Users Group, 1996/08/08
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>>It sounds to me that the M6 and Pentax are calibrated a stop down in
>>exposure biasing them for transparency film, where the other cameras
>>are at the nominal value which would be best for negative films.
>>
>>I dunno. I use a meter as a guide and modify the readings with my head.
>>I dont know which direction my head is biased but I like the pictures
>>I take. :)
>
>I wrote the original message. I do not want people to draw conclusions like
>that yet. There are other factors that affect meter calibration. I simply
>reported the results, but they raised more questions. Please stay tuned.
I'm quite familiar with calibration and specification testing.
I've seen camera/meter combinations that were all within test
specification and differed by .5-1.5 EVs. Purely conjectural that
the manufacturers intended it that way, but I was interpreting,
not being technically rigorous.
>I don't understand the reasons for the differences. They may have been
>affected by the focal lengths used and the internal construction of the
>different meters.
Certainly.
>My only finding so far is that a new Varta PX625 U battery seems to be less
>than one/half stop off relative to the mercury PX625 battery.
My biggest concern and that which would affect picture taking the
most is what happens as the PX625U batteries age. The power
delivery curve of the mercury-oxide and silver-oxide battery is
very flat with a very fast drop off below a certain voltage,
where alkalines have a current demand response that tapers off
more as voltage drops, with a less severe cutoff characteristic.
Also, since the initial current is higher than the spec for which
the CdS systems were designed, I wonder what the long term
affects of overvoltage use of those systems means in terms of
degradation over time, etc.
I can deal with readings which are a bit high or a bit low, as
long as they're consistent. Each of my cameras with meters in
them read a little differently and I've learned how to compensate
for such behaviors with each camera. The shutters and apertures
of all of them are not entirely perfect either so there remain
some things that are beyond the scope of meter accuracy when it
comes to producing pictures.
As a general observation, too much weight is lent to
specifications and numbers these days. My own photography is less
dependent upon super accurate exposure systems and ultimate
resolution while being more affected by image composition,
timing, and how my understanding of the media allow me to push it
to achieve the results I want. For me, photography is less a
scientific metric and more of an expressive communications
medium.
Godfrey
Three cheers for the Kodak Pocket Guide and exposure calculator!
:)