Re: Quoting EI

["Sandor Mathe" <sandor.mathe@xxxxxxxx>]

George L Smyth <GLSmyth@xxxxxxx> wrote:

> Elton N. Kaufmann - Cycloid Fathom Group wrote:
> > 
> > I have found some of the posts that quote EI difficult to understand
> > because I don't know what device is measuring the exposure (camera's
> > internal meter or separate meter) and through what filter, if any, the
> > exposure is measured.  Perhaps a convention for quoting EI was established
> > before  I joined the list?   
> 
> You are right in that there is no real convention for this.  Quite some time back it
> was suggested that we use "TTF" to indicate that a measurement was taken "thro
ugh the
> filter."  I have tried to indicate that my measurements are specified as being made
> through the filter in most of my posts (this method makes the most sense to me, with
> the obvious exception of an opaque filter), though certainly there are posts where I
> have not indicated this.
> 
> I agree that we should attempt to make some form of explanation concerning the
> metering process.  "TTF" is good shorthand, perhaps "not TTF" can indicate a separate
> unfiltered measurement.

The main drawback (potentially anyway) of TTF meter readings is 
whether the light meter or more importantly your light meter versus 
mine react the same to the strong filtration of a 25 or 29 Red 
filter.  They likely react about the same to the 87 opaque :-)

The whole set of discussions on the Zone VI modifications to the
Pentax spot meters and whether they are effective in this or not
come into play.  As I understand it they allegedly match the
spectral sensitivity of the light meter to the sensitivity of the
film (Tri-X?) so that if you measure several spots TTF you will get
the same representative densities on the film regardless of what 
colour filter you use.

With the huge variety of light meters in-camera and hand held, that 
are in use I would think it is safer to use Elton's method for 
comparison between workers.

Sandor Mathe  -- sandor.mathe@xxxxxxxx
(905) 670-1225 x333  --  FAX (905) 670-1344
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End of Infrared-Digest V0 #289
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