Re: [OM] Auto Exposure on OM4T(Long)

[Winsor Crosby]

> On Thu, Apr 25, 2002 at 11:00:47AM -0700, Winsor Crosby wrote:
> >  >
> >  >
> >  >Film reflectance is a issue for testing guy`s but not for practical work.
> >  >The difference it nomimnal and real film-sensivity already outweight
> >  >  this problem.
> >  >
> >  >Frieder Faig
> >
> >  That is not really true. If you consult the archives as I just did
> >  you will find discussion of this issue. Before Gary Reese did his OM
> >  lens tests he also measured the reflectance of various films and
> >  found at least a 1 stop difference, if I remember correctly, between
> >  the highest and lowest.
> My statement is based on meassurements published  in a photo
> magazine in 1979 when testing the OM2n.
> The min-max differences were:
>   slide films:  +0.4 ..-0.2 stops
>   print films: +0.2 .. -0.2 stops
>   b&w: +0.2 .. -0.3 stops
>   high contrast copy film: +0.8 stops
>
> With one exeception all film-types don`t differ more than 0.6 stops,
> wich is +/- 1° ISO difference.
> The differences between slide-film-reflectance  in Gary`s test were
>  within the 0.5 stops area. The print-film differ more, But they also
>  have more lattitude.
>
> When I`m concerned about exposure differences in the 0.3 stops
> area, I`m using spot metering anyway, and not average metering.
> And you need self tested film type dependant iso-setting for this
> accurancy at all. I don`t worry about film-reflectance.
>
> Frieder Faig
Is there even one film that was tested in 1979 that exists unchanged 
today?  You might find it interesting to look at this URL:
http://www.markcassino.com/essays/ttlflash.htm , which discusses the 
issue and has a picture of the the different colors and shades of 
unprocessed film. It also mentions a problem with the light color of 
Kodachrome resulting in the underexposure of flash pictures.
I tend to use the spot meter too, but I was concerned about those who 
use the center weighted auto exposure.  It would also affect the use 
of TTL flash.
--
Winsor Crosby
Long Beach, California

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