It may be that when the OTF system was designed no common film had more than a
1/3 stop reflectivity difference from the average, but as Giles' post shows
that is hardly the case now, with there being a 1.3 stop difference between
Kodak Gold 800 and Kodak Gold 100.
It does make me think that I should be spot metering all my shots if only to
eliminate the OTF variable, though of course there are other good reasons to do
this anyway. That doesn't help with TTL flash, but knowing the reflectivity
assumed by the designers we can make adjustments.
BTW, I made a quick and dirty test of Kodachrome 64, and it reflected about 1/3
stop more than the 18 0ray card.
Chip Stratton
cstrat@xxxxxxxxx
> -----Original Message-----
> From: owner-olympus@xxxxxxxxxxxxxxx
> [mailto:owner-olympus@xxxxxxxxxxxxxxx]On Behalf Of Hans van Veluwen
> Sent: Thursday, October 14, 1999 7:05 AM
> To: olympus@xxxxxxxxxxxxxxx
> Subject: Re: [OM] Assumed reflectance of film for OTF
>
>
> : I've seen the work by others which shows reflectance values for different
> films
> : compared to an 18 0ray, but can we assume that 18 0s the value assumed by
> the
> : Olympus engineers?
>
> Olympus investigated the reflectance of 55 best selling films and
> averaged it.
> They found no more than 20 0eviation (= 1/5 stop) from this average
> in colour
> film, and 30 0eviation (1/3 stop) in b/w film.
>
> Source: Die Welt des OM Systems, Franz Pangerl. He claims to have asked the
> question to Maintani himself. He also names three films that have too much
> deviation because of their strong surface color: Agfaorto 25, Orwo NP 15 and
> Kodak IR b/w film.
>
> H@nz
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