BTZS, Zone System, Everyone Else... Film Speed ?

[Chuck P.]

A spot meter measuring a known target (say a grey card or some such thing at 10 meters) and an incident meter used at the same place the card is placed will lead you to the same camera setting. (Dunn & Wakefield, Exposure Manual)

Taking the gray card out of the discussion------I don't put one in the important shadowed area before reading the luminance from it. The luminance of a particular surface may very well be darker than a gray card in the same shadow, on the surface anyway, I question it. It's an interesting point though as I see it, I'm going put this to some practical experiment the next time I'm photographing.

[Captain_joe6]

I feel like we're missing the part where someone says something to the effect of "ISO can only be accurately and repeatably determined under exacting scientific standards in a laboratory setting, as per ISO guidelines, which may differ greatly from field conditions with various manufacturers' equipment and calibrations of a multitude of other instruments and chemicals in the photosensitive-optical construct" followed by several threads where others say "Yes, except...," and finishing no closer to where we started, with all confused, many frustrated, and nobody confident of their technological skills anymore.

Did I miss that part somewhere?

I've had a couple of beers today.

[Mark Barendt]

Taking the gray card out of the discussion------I don't put one in the important shadowed area before reading the luminance from it. The luminance of a particular surface may very well be darker than a gray card in the same shadow, on the surface anyway, I question it. It's an interesting point though as I see it, I'm going put this to some practical experiment the next time I'm photographing.

The magic is having a/any "known" target not necessarily a gray card; grass is a reasonable substitute, concrete, granite...

If the relationship of the target to the film speed is known it works.

[Bill Burk]

But doesn't the same situation hold for the camera? if its lighter for the meter, it stands to reason that it will be lighter to the camera as well, no?

Yes. And you can see it with your eyes too.

[Bill Burk]

I agree that haze and flare, as well as sample size, affect spot readings and you actually are helping me make my case, as is Sandy.

What I'm getting at is that the thought that "spot meters are better when it isn't easy to get close to the subject" just isn't real.

Without getting at the concept of "better"... Spot meters are good at estimating what will reach the film because the optics leading to the sensor are similar to the optics leading to the film.

I use spot readings and do sanity check with incident readings. So I know I can trust both.

[Mark Barendt]

...the optics leading to the sensor are similar to the optics leading to the film.

How so? What optics?

[Bill Burk]

I feel like we're missing the part where someone says something to the effect of "ISO can only be accurately and repeatably determined under exacting scientific standards in a laboratory setting."

Ah yes. I've given up trying to achieve ISO conditions. I have repeatability. But my accuracy is only within 2/3 stop. So that leaves me with theoretical discussions, occasional demonstration of concepts. And the best part... Developing film and making prints.

You haven't seen recent work by me because I used up my supplies... but I've been shaking the boxes under the tree and one of them feels like paper.

[Bill Burk]

How so? What optics?

Just the spotmeter lens, similar to the camera lens.

[Chuck P.]

Without getting at the concept of "better"... Spot meters are good at estimating what will reach the film because the optics leading to the sensor are similar to the optics leading to the film.

I use spot readings and do sanity check with incident readings. So I know I can trust both.

I do spot readings too, but the sanity check is confirmed with the negative, happy to report I am still sane after several years.

[cowanw]

I am reading Ansel Adams Examples and was amused to read
"He (Edward Weston) relied for his first exposure on his personal approach to the use of the exposure meter, usually doubling the indicated exposure.
If Weston considered that film speeds should be halved, who am I to say different.