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

[Chuck P.]

I meter in spot fashion and employ the ZS technique, I can read any shadow from the camera's position along the lens axis------what does a BTZS user do when he can't directly measure a shadow area because he is unable to reach it? If you can reach the shadow with your incident meter and take a reading, it may not provide the same luminance value while "in" the shadow as it may from the camera position, in fact it could be quite different.

[sanking]

I meter in spot fashion and employ the ZS technique, I can read any shadow from the camera's position along the lens axis------what does a BTZS user do when he can't directly measure a shadow area because he is unable to reach it? If you can reach the shadow with your incident meter and take a reading, it may not provide the same luminance value while "in" the shadow as it may from the camera position, in fact it could be quite different.

Let me clarify a couple of points.

First, any system of metering, either for film or digital camera, requires some type of creative interpretation.

Second, BTZS is not based exclusively on either incident meter readings or reflective metering with a spot meter. The testing provided data that allows field use of either incident metering or a traditional zone system type spot metering.

Third, even if only incident metering is used a single shadow value reading is not the only viable method. One could 1) take a single shadow value reading and double the EFS, 2) take a shadow value reading and a highlight value reading and average the two, or 3) take a single highlight reading and halve the EFS.

Whatever method you use the critical issue is one of choice, i.e. determining which area of the subject contains the appropriate shadow values for your creative interpretation.

Finally, to directly address the question, one can nearly always find shadow areas near the camera position that approximate the luminance values of shadow areas in the subject that can not be reached with the meter. If not, then one can always resort to a spot reading.

BTZS is not an either/or, brain/no brain system. Rather, it is based on the concept that the photographer understands his/her materials and equipment, and knows how to use both creatively to achieve a desired end.

Sandy

[Chuck P.]

........... to directly address the question, one can nearly always find shadow areas near the camera position that approximate the luminance values of shadow areas in the subject that can not be reached with the meter. If not, then one can always resort to a spot reading.

Thanks for that answer. Now, I wander, do most BTZS users carry both a spot meter and incident meter with them, I figure most use a nearby shadow.

The other points you made are, of course, understood, except I always thought (quite erroneously it appears) that BTZS was incident meter oriented because that always seems to be the context with which it is discussed.

[Mark Barendt]

I meter in spot fashion and employ the ZS technique, I can read any shadow from the camera's position along the lens axis------what does a BTZS user do when he can't directly measure a shadow area because he is unable to reach it? If you can reach the shadow with your incident meter and take a reading, it may not provide the same luminance value while "in" the shadow as it may from the camera position, in fact it could be quite different.

Actually, as i understand it, the distance itself doesn't matter as long as the spot meter reads only the target. The luminance of a point source doesn't change with distance, just it's significance/relative size within the scene. Haze and flare are a separate issue.

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)

One problem for spot meters is that as distance increases the sample size for the spot meter increases, at 100 meters you would need a pretty big card, at 1000 meters you might need the short side of a barn. Even a 1-degree spot starts becoming an averaging meter as distances become significant.

A second problem for spot meters is that the targets in the scene aren't always "knowns" like a grey card is. Many times the target, especially at a significant distance, is a muddled mess.

Looking out my front door right now at 100 meters I would be hard pressed to get a 1-degree reading that didn't include both dark green trees and snow. How much of each...? Who knows?

Incident meters, on the other hand only require getting into or reading some portion of the same lighting the subject is in.

For an open shade reading this is really, really, simple in most any situation; if you are inside or under something go outside where the meter can see the sky, dome extended/out, point the meter away from the light source, and take the reading, apply the offset and set the camera. This works whether or not you can see the light source directly.

[Bill Burk]

Sandy's post is worth reading twice.

BTZS is a comprehensive book with chapters on spotmetering and sensitometry. It "goes beyond" Zone System by teaching duplex incident metering. But you can spotmeter too.

Back when the book was written, you could simulate scene shadows by bending over and holding the meter a certain way in the shadow of your puffy down jacket. I don't think anyone wears jackets like those anymore, so I don't know if it's possible to re-create the effect. Certainly the subject will refuse to wear glasses that big. (Sorry couldn't resist poking fun at the 70's look that had me giggling the whole way through that book - I see no fault with the teaching).

Traditional Zone System testing comes up with Exposure Indexes that disagree with rated speed because of the way the testing is done. Stephen Benskin has ideas what is behind that: Partly it's due to flare, partly due to using 7 stops instead of 7 2/3 stops. Partly from using a different statement of quality - traditional standard was visual match looking at prints.

[sanking]

Thanks for that answer. Now, I wander, do most BTZS users carry both a spot meter and incident meter with them, I figure most use a nearby shadow.

The other points you made are, of course, understood, except I always thought (quite erroneously it appears) that BTZS was incident meter oriented because that always seems to be the context with which it is discussed.

I believe your assumption that BTZS is incident oriented is correct. My point is simply that it is not limited to incident metering, and certainly not to the one kind of incident metering being discussed, i.e. single shadow value reading.

My main meter is a Sekonic L-558, which can be used either for incident readings or as a 1º spot meter. Newer models of the Sekonic also offer either incident or spot metering.

Sandy

[Bill Burk]

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).

That compares "Spot Meter" and "Incident Meter"

But I get different results when comparing "Spot Meter" and "Reflected Meter" where the reflected light reading is close to the subject, and spotmeter is taken from camera position.

Simplest proof is to take spotmeter reading of the shadow under a car. Then walk up to the car, bend down and take another spotmeter reading. The close-up reading will indicate the shade is deeper/darker.

I believe the primary issue in this case is flare. You touch on the problem Mark, when you look out your front door and see grass and snow.

Faced with your scene, I would use Zone System... Spot the darkest thing I think will be worth seeing in the picture and decide to place it on Zone II or III depending... I would not hesitate to turn the knob to incident mode for a quick sanity check of the reading.

[BetterSense]

Simplest proof is to take spotmeter reading of the shadow under a car. Then walk up to the car, bend down and take another spotmeter reading. The close-up reading will indicate the shade is deeper/darker.

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?

[Mark Barendt]

That compares "Spot Meter" and "Incident Meter"

But I get different results when comparing "Spot Meter" and "Reflected Meter" where the reflected light reading is close to the subject, and spotmeter is taken from camera position.

Simplest proof is to take spotmeter reading of the shadow under a car. Then walk up to the car, bend down and take another spotmeter reading. The close-up reading will indicate the shade is deeper/darker.

I believe the primary issue in this case is flare. You touch on the problem Mark, when you look out your front door and see grass and snow.

Faced with your scene, I would use Zone System... Spot the darkest thing I think will be worth seeing in the picture and decide to place it on Zone II or III depending... I would not hesitate to turn the knob to incident mode for a quick sanity check of the reading.

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.

I'm not dissing spot metering here, they do have certain creative advantages like easily tying any specific tone in the scene to the film curve at a specific point regardless of the overall lighting. It's not that you can't get there with an incident meter, just that the thought process is more direct with a spot meter.

[Mark Barendt]

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, I would suspect more so even. I would guess that a 1-degree spot meter should be less affected than most lenses just because of the field of view. That's pretty much why a 1-degree spot is used, basically to exclude the influence of the rest of the scene.