Re: [Rollei] Incident v. reflective

["Dirk-Roger.Schmitt]

Hi folks

>Velvia is, in fact, ISO 50.  There are very strict standards and procedures
>for determining ISO speeds.  The fact that many photographers like the
>results better when they rate it at 40 or 32 does not change that.  When you
>set your camera to a number other than the rated ISO number that is not an
>ISO speed but an EI, Exposure Index.


In fact, I only shot one roll of Velvia to test my XF 35 for "Point and 
Shoot". The images were extremely sharp - due to the Sonnar lens - but I 
felt that all slides were a bit too dark. I was relating that to the meter 
of the XF 35, but maybe this is an effect of that film The next time I 
shall try with 40 or 32 speed setting at the camera!


> > The .5 stops difference can be attributed to the gray card.  Although all
> > claim 18% I have seen a slight variance between alleged gray cards.
> >
>
>The Kodak Gray Card is manufactured to incredibly tight standards and is
>precisely 17.8something in reflectance.  I don't recall the exact number,
>but they have it specced very precisely.  The only time a Kodak Gray Card
>will have a different reflectance is if it has faded from being left exposed
>to light.  It is a good practice to replace them ever few years.
>
>I'm not sure what .5 stop difference you are speaking of above, but the
>difference between a gray card and standard reflectance to which meters are
>calibrated is .5 stop, the difference between 12.5% reflectance and 18%.
>This is why the Gray Card instructions tell you to make a half stop
>correction from your reading off the card.


Bob, now I am getting more confused and more crazy......

I have a new "Non Kodak Grey Card" from "Bildwand". The benefit of that is 
that it is made of plastics and is washable. The Sun fading resistance is 
given with 7-8 on the "Blauwollskala" (translated: blue wool scale) 
whatever that means. The reflectance is specified to be 17.68 % without 
giving tolerances.
I made now, just a few minutes ago the followign test:

Illumination of the card,
setting of all meters to ISO 100

Measuring reflected light by Gossen meter 1: 1/8 s, f = 8.0
Measuring reflected light by Gossen meter 2: 1/8 s, f = 8.0
Measuring incident light by Gossen meter 1: 1/8 s, f = 5.6 + 0.8 stops 
(i.e. 2/10 stops close to 8.0)
Measuring incident light by Gossen meter 2: 1/8 s, f = 8.0

Measuring with Rollei 6008 in spot mode: 1/8 s, f = 5.6
Measuring with SL 35 E 1: 1/8 s, f = 5.6 + 0.5 stops (i.e. between 8.0 and 
11.0)
Measuring with SL 35 E 2: 1/8 s, f = 5.6 + 0.5 stops
Measuring with SL 350: 1/8 s, f = 5.6 + 0.5 stops
Measuring with SL2000: 1/8 s, f = 5.6 + 0.5 stops
Measuring with R 35 1: 1/8 s, f = 5,6 + 0.5 stops
Maesuring with R 35 2: 1/8 s, f  = 5,6 + 0.5 stops
Measuring with XF 35: 1/8 s, f = 5.6 + 0.5 stops (if the values shown on 
the scale recalculated to 1/8 s)
Measuring with R 2,8 F: 1/8 s, f = 5.6 + 0.5 stops
Measuring with Olympus E 20: 1/8 s, f  = 5.6  stops for whitebalance   < 
4000 K,   f = 5.6  + 0.3 stops for whitebalance >=  4000 K  (values 
after  recalculated for ISO 100, Olympus is specified for 80 ISO)


That means, that the Gossen world is consistent and that the Rollei 
world  seems also consistent, where the 6008 overexposes a bit compared to 
the others. Even the Olympus seems to be o.k., although I do not understand 
the differences for different white balances, as white balance is 
calculated after exposure from the raw data.

My questions: Where is the reason for the discrepancy between the Gossen 
and the camera world?

And Bob: What is the reason to give half a stop more? Which types of meters 
are calibrated to 12.5 %? Could it be that the camera meters are calibrated 
to 12.5 % and the Gossen meters to 18 %?
I thought, the idea of the grey card ist just to measure it and to expose 
like the measurement on it.



> > Last, the 1/3 stop for reflective meters is consistent with what I have
> > found as well.  It may seem odd but perhaps the camera makers are
> > adjusting the meter to be slightly more overexposed. For this reason
> > when I am not with meter I use a variation of the Sunny 16 rule.
> > I set the shutter to the next higher speed for a given ISO and use F11.
> > The reason for this is that is allows for about a 1/3 - 2/3 overexposure
> > compared to the Sunny 16 rule. It also accounts for shadows.
> >
>
>Generally point and shoot and low end SLRs are set to overexpose on the
>theory that they are being used with color negative film.  Pro cameras are
>usually set up for proper exposure on transparency film.

Look at my measured values for the 6008!!!  Here, the discrepancy to the 
Gossen world is one stop.


Best greetings


Dirk

P.S. I am myself very suprised of the extremely high consistency of all 
cameras!!!!  Although in practice there are much more differences. They 
must come from the different averageing techniques the different meters are 
doing and this will yield to further problems.....

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