Pentax Digital Spotmeter: Standard vs. Zone VI

DREW WILEY said:

Well I care, Richard, because an "odd" film that is still in production and happens to be one my favorites in ACROS, which is not standard Panchromatic at all, but Orthopan, and there's simply no way anyone can bend the logic to say metering is the same.

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Hi Drew,

ACROS has been my standard film for over 20 years, being (almost) the only film I shoot in 35mm, 120, and 4x5.

I've gone through hundreds of rolls and many hundreds of sheets of it.
I currently have 200 sheets in the freezer, and just today received another 100 sheets from Japan.

I've never had any problem properly exposuring ACROS using any system, from Nikon F3HP to Sekonic L-558 metering.

The point you're missing is that the ASA rating of a film is not some number cast in concrete, delivered from on high.
It's the number that must be plugged into an ORDINARY exposure meter to yield proper exposure of the film.
It's determined by the film manufacturer by testing. Any bias in the metering technology is corrected in that process.

- Leigh

Alan Klein said:

Do you sleep with the person who gave you the meter as a gift?

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Already "put a ring on it"

You're missing the point entirely. If you meter thru a red or green filter based on a particular meter allegedly seeing the same way film does, ACROS
is going to respond differently than ordinary pan film. Merely adjusting the ASA, deliberately or subconsciously, only works to the spectral cutoff point
of the film in the red, and won't correct for what is therefore a significantly different amount of dip in the green. If you are fully accustomed to a particular meter with a given film and it somehow itself sees the whole spectrum, you just chalk it up to experience, not the accuracy of the meter -
no different that basing exposures on sheer memory, without any meter. In my own work, not understanding such distinctions would constitute the
difference between approximately exposed negative and ones which truly sing in the extremes, in other words, the difference between a very successful long trek in the mtns with a heavy gear load, and a comparative bellyflop, photographically. Merely overexposing ACROS to push it further
up the film curve won't salvage something it can't see to begin with. It sees some red, but only to a certain point.

To elaborate a bit ... Light meters aren't spectrophotometers. They have inherent biases relative to the spectrum which must be understood in advance relative to the sensitivity of the film itself. So back to our example of ACROS: Someone reads that to make pan film see values more like
ordinary human vision, put a light green no.11 filter over the lens. So they do it and it reading with a modified meter and it seems to work. But then,
having learned this, they try it with ACROS instead, and their greens (relative to other hues in the scene) come out all bleached-looking, overexposed, just as if a very deep green filter had been used instead. The reciprocal effect in the red can be easily tested and proven (if someone
simply refuses to believe the spectrogram on the Tech sheet) - take you usual 23A or 25 red filters and make exposures. Then go a step further into
the red with a 29. Even correcting for the extra density with either a filter factor or reading through the filter with a meter isn't going to proportionately salvage the deep shadows, because the light that passes through that filter is simply too red for the film itself to see, no matter what
the meter is telling you is going on. Of course, if you shoot a true ortho film, you won't get red exposure, period, though many things in nature are
actually more complex than what the unaided eye initially assumes. This fact isn't faulting the modified Zone VI meter any more than any other meter. You just have to understand any inherent limitations and plan accordingly.

Drew, if you really want to compare published data...

ACROS has slightly better red sensitivity than TRI-X 400:
Also, ACROS has slightly higher yellow/green sensitiity v. blue, while the opposite is true for TRi-X.
(The three graphs are aligned vertically at 600nm. The chroma chart is a bit narrow.)



- Leigh

Xia_Ke said:

Already "put a ring on it"

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Then you already have your answer of which to keep

Since filter manufacturers don't know what film you;re using, their recommended factor is a guess too. How will not reading the meter thru the filter make a difference? At the end of the day, don;t you have to keep some notes to get a feel what a particular filter is doing with the film you use? Won't you come up with a pretty specific adjustment factor either way that's relatively repeatable?

Alan Klein said:

don;t you have to keep some notes to get a feel what a particular filter is doing with the film you use?
Won't you come up with a pretty specific adjustment factor either way that's relatively repeatable?

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The filter will always do EXACTLY the same thing with a given film.

What varies are the subject and the lighting.

The human eye is a terrible judge of color.
If you don't believe it just look at a printed page in room light and then in daylight. It looks white in both cases.

- Leigh

But but but... the differences in spectral sensitivity of a given B&W film, and how it affects your personal metering equipment, and what you do with the data your meter gives you... don't those factors also fall into place with the ISO tuning that works best for your process and developer, your development time, temp, and technique... all the things that make "my" process (from visualizing to final dried neg) differ from "your" process? Isn't all of that a fairly moot point to anyone who chooses a film and gets to know its characteristics?

Sure, spectral issues could mean you come back from the forest and find the greenery didn't expose as expected... the first time you tried it. Seems like you'd learn to deal with that if you continued your relationship with a given film.

In 20-some years of photography, I've never once thought of spectral issues when shooting B&W, other than filtering for contrast of specific color areas (orange filter for blue skies and that sort of thing).