Latitude of Reversal film compared to Colour Negative

DREW WILEY said:

In certain applications there ARE fixed standards of calibration.

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Yes... but calibration of light meters for photography is covered by norm ISO 2720:1974 (Cameras with internal meters, ISO 2721:1982), for the C constant the norm recomends a value between 320 to 540, Minolta used 320 and Sekonic 340.

Then we have the K, the norm recommends between 10.6 to 13.4... Sekonic, Nikon and Canon use 12.5 while Pentax and Minolta use 14. From that different K we have a 1/6 stop change.

Then we have different spectral sensitivities...

...but what really it has a great impact is the way we meter !


Well, in practice we all make an adaptation of the exposure policy to our particular gear, to our particular taste and to our particular metering way... so no problem...

@138S: So what you're saying is that no light meter can possibly be accurate, and photography is a waste of time?

grat said:

@138S: So what you're saying is that no light meter can possibly be accurate, and photography is a waste of time?

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The differences are realistically below any noticeable threshold - and are less than many shutters' variances - even on narrow latitude transparency. Every other variable (including processing variability) would need to be dealt with before the meter really becomes an actual problem. A lot of it is promoted by people who (funnily enough) need to sell you their specific meter...

Somewhere I still have an early Weston no-battery meter I inherited. About all it's good for is telling which direction the sun is ...maybe. And it still works as badly as it ever did.

Lachlan Young said:

The differences are realistically below any noticeable threshold - and are less than many shutters' variances - even on narrow latitude transparency. Every other variable (including processing variability) would need to be dealt with before the meter really becomes an actual problem. A lot of it is promoted by people who (funnily enough) need to sell you their specific meter...

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Since I send out to develop at a pro lab, I question just what their procedures are from one time to the next. In any case, I can always blame the lab if the exposure comes out wrong.

grat said:

@138S: So what you're saying is that no light meter can possibly be accurate, and photography is a waste of time?

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Not at all, let me sumarize:

> Meters have a "by desing" small variability depending on manufacturer, perhaps under 1/4 or 1/3 stop.

> That variability can be larger when metering on saturated colors, because of differences in the spectral sensitivity.

> The way we meter has a way larger impact in the metered value in challenging scenes, for example matricial vs ponderated may deliver more than one stop if we simply include the sun in the framing, to not say what ponderated mode does in a sunset if sun is in the center... if we calculate manually the exposure from different spot meterings in the scene then our decision making adds additional variability.

> Meters are not a waste of time because we adapt EI to the way we meter and how our gear works, we apply a feedback.


So what I say is that it has little sense to discuss if overexposing 1 stop (or not ) is benefical until we say how we meter, in what kind of scenes and with what gear (incident vs reflective, for example).

The point I was trying to make, although I used excessive snark, is that you seem to obsessing over the minutiae, and ignoring the fact that people are using these meters quite well.

Your example of how various cameras meter is a bit disingenuous, because those meters are designed to work with those cameras, and the people writing the algorithms to determine proper exposure for those cameras, are aware (or dictating) the sensitivity of the individual cameras. Further, no human input is really used, so it's not relevant to the discussion-- well, the tangent to the original discussion, anyway.

Also, suggest "weighted" instead of "ponderated". It's not wrong, but "weighted" in the context of metering is a more familiar term.

Alan Edward Klein said:

Since I send out to develop at a pro lab, I question just what their procedures are from one time to the next. In any case, I can always blame the lab if the exposure comes out wrong.

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If they are running good process controls, their density should be pretty invariant - with possible very small changes in colour balance. What I was talking about was lab-to-lab density variance - which, if process controls are in range, should again be very small - and certainly under 1/3 stop - which unless you had a set of direct visual comparators, might still be less than obvious. Point being, that the variables in all the other parts of the system that are involved have potentially greater variance than a small variance in light meter behaviour - and that if your meter is in good order, and with sensible technique you are getting acceptable transparencies of landscape/ scenic subjects etc, you should be fine. Things are slightly different if you are trying to get absolutely 'accurate' reproduction of an object for reproduction/ commercial purposes - and even then, I'd question why you'd be using transparency for something that correctly inverted colour neg is much, much better at.

grat said:

Also, suggest "weighted" instead of "ponderated". It's not wrong, but "weighted" in the context of metering is a more familiar term.

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Yes, you are right. English is my 4th language and not always I find the right term.

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Of course, people use meters quite well... no doubt. But many people rate film at different EI, in part because the way people use the meter is different, or at least what I suggest is the different EI speeds used by different people in part are not that different, because the EI hides a different metering policy.

I recall that time ago I understood better the complexity of metering after reading the second half of Beyond The Zone System, my view a bit comes from my interpretation of what I learned then.