BTZS + Modern Incident Meter w/ Digital Readout

[Ken Lee]

"Following the above steps I am imagine this: shadows = EV 8; highlights = EV 13."

Although reflective and incident meters each have pitfalls, one of the core value propositions of incident metering, is that we don't have to decide which subjects belong in which "Zones". The Zone System facilitates Pre-Visualization, but the flip-side of that, is that we often take our best guess about what belongs where.

That a B&W viewing filter is popular with Zone System users (myself included, after 40 years) is revealing. For example, see that pumpkin over there ? It kinda looks like Zone IV to me, but is it ? Should it be ?

[Shen45]

Steve,

Thanks for the quick calculations on my behalf. I wasn't expecting a free tutorial in BTZS, but your reply helps my conceptual understanding.

Jonathan


EDIT: I've still got my old Palm III lying around. You mean it can still be used for something?

I actually have an old Palm 111 as a back up. Works wonderfully.

[Shen45]

Sorry about the deleted post. Ken your observation re incident and BTZS are spot on. With spot metering you can meter a section of your scene and put that ev into the a test area of the ExpoDev and it will give you a "zone" that the film you have tested will render it on the particular paper you are using. Quite useful.

[jcoldslabs]

Incident vs. spot. That makes sense.

Jonathan

[Ken Lee]

I have already purchased Plotter program, and am waiting for the iPhone version of ExpoDev to come out.

I intend to measure my scanner and use it in place of "paper".

While it's great that both systems are supported, if I switch to BTZS I will work within its parameters instead. It's hard to teach an old dog new tricks, but it's good to keep... stretching.

[sanking]

Ken,

I believe you own the 3rd edition of Beyond the Zone System. If that is true, please read carefully pp. 111-114, which covers The Standard Gray Card. Some of this may seem a bit obtuse, but the basic issue is that the 18% gray card (and the 18% light transmitted by the incident cone) is not really middle gray as used by ANSI standards for meter calibration of a seven stop, or log 2.1 range. Apparently the use of the gray card ordinated in the studio where the luminance range of copy subjects is 5 stops, or log 1.5.

Sandy

[cowanw]

read here
http://www.apug.org/forums/archive/i...p/t-36416.html
an amazing thread on many levels but if you keep at it a lot of insight into the different way people think on these things

Ken (or anyone),

I am not steeped in BTZS methodology, but I have a basic (and probably stupid) question regarding steps 1-4 in the opening post. I use a Pentax Digital Spotmeter and to find the SBR I just meter the brightest spot where I want detail and the darkest spot I want detail. The difference in stops is the SBR--or so I have assumed.

Following the above steps I am imagine this: shadows = EV 8; highlights = EV 13. Difference = five stops. Add that to 5 and you get 10 for the SBR. Huh?

Feel free to smack me upside the head and tell me to get Phil's book, but I am curious as to why it seems so complicated.

Also, Ken, I thought the Pentax meter's LED viewfinder display was in EV numbers. Is that not the case?



Jonathan

[Ken Lee]

I believe you own the 3rd edition of Beyond the Zone System. If that is true, please read carefully pp. 111-114, which covers The Standard Gray Card.

Thanks - I now have the latest edition as well as the 3rd edition - just to make sure I don't miss anything. Obtuse is a good word

There appear to be 3 basic principals at work. They intersect as follows:

The first principle is that exposure and development time often need to be adjusted to accommodate subject brightness range, and film speed varies with development time. So when taking a photo, it's best to measure the SBR first, set film speed accordingly, and develop accordingly.

The second principle is that 18% is a traditional number, but not the correct midpoint for subject brightness. It's actually 12.5%, or even 9% if we do the arithmetic. Therefore, metering the reflection off an 18% gray card will result in 1/2 stop underexposure if we consider 12.5% to be the correct average gray. If we use 9%, then we're underexposing by a full stop. Since incident meters are also based on the (wrong) 18% standard, they also give us readings which result in 1/2 stop underexposure (or 1 stop, if we use the 9% value)... unless we work around the problem.

How we work around the problem, is the part that gets obtuse :-)

The third principle is that we must base our exposure on the shadow (low) reading, because it's critical with b&w negative film. ("Expose for the shadows, develop for the highlights").

The obtuse part is that simply metering for the shadows would normally result in overexposure, since shadows need to be dark. However, we know that the incident meter is going to give us a reading by which we will be under-exposing by 1 stop. So it ends up OK in the end.

Is that it, in a nutshell ?

[Mark Barendt]

Ken,

Incident meters aren't necessarily calibrated to 18%. My understanding is that they are closer to 12%. The standard though is a range not an absolute number, manufactures can vary their calibration within the range.

The other factor at play is EI. Our personal testing to get to an EI (a personal film speed to meter calibration) is not normally done to ISO or ANSI laboratory standards and very posibly not even using the same benchmarks for speed point.

Personally in find no underexposure when using my incident meters at box speed on any film. Granted my observation is as subjective as anybody's but that's pretty much the point I'm trying to make.

[Ken Lee]

Ken,

Incident meters aren't necessarily calibrated to 18%. My understanding is that they are closer to 12%. The standard though is a range not an absolute number, manufactures can vary their calibration within the range.

The other factor at play is EI. Our personal testing to get to an EI (a personal film speed to meter calibration) is not normally done to ISO or ANSI laboratory standards and very posibly not even using the same benchmarks for speed point.

Personally in find no underexposure when using my incident meters at box speed on any film. Granted my observation is as subjective as anybody's but that's pretty much the point I'm trying to make.

Beyond the Zone System, Fourth Edition, page 116, paragraph 2 (emphasis mine):

"The milky plastic dome accepts light from a very wide area - approaching a solid angular field of 180 degrees - and transmits approximately 18% of the incident light to the cell underneath so that the meter provides the equivalent of a three-dimensional gray card reading...

...Neither luminance meter nor incident meters can provide direct, accurate exposure data for most subject conditions. If you want precise data, you must always use special metering techniques or modify the meter's recommendations, or both."

Page 118, paragraph 2 (emphasis mine):

"Because the incident meter's cell always sees 18% gray, it will do the same thing if you follow the meter's recommendation without modification."

Page 132, paragraph 2:

"... basing camera settings on a single shadow reading will typically result in overexposure of about 1 stop."

Page 134, paragraph 4 (emphasis mine):

"Next consult the effective film speed chart (figure 9-10a) to find the film speed number appropriate for the SBR, and set it into the meter dial in place of the official ISO film speed. Notice that these film speeds seem exaggerated: they are, in fact, just double the normal film speeds. As explained earlier, this is done deliberately to compensate for the 1-stop overexposure that normally results when the camera settings are based on the low-light incident reading."

So, relying on an 18% meter gives 1 stop underexposure, but reading the shadows gives 1 stop overexposure. Then, by using an effecitve film speed appropriate for the SBR (derived from careful testing), we get the right exposure. Then we develop to match the SBR. It sounds perfectly coherent.

If all of that works together, then the only part I don't follow, is his suggestion that effective film speeds have been doubled on purpose. I thought that EFS is determined through testing, and is not tied to box speed, or boosted according to any "canned" value whatsoever. In fact, nowhere in his instructions on incident metering, do I see a recommendation to use box speeds or any arbitrary correction factor. That would seem contradictory to the whole spirit of individual testing and calibration.

It may be that in a book of this size, no author can keep track of all the changes made through 4 editions, and the result is that a few sections of the book don't agree with one another. It wouldn't be the first time