Incident metering: Hope my confusion will be resolved with this.

[baachitraka]

Incident meter: It just tells you amount of light falling on a subject, which is equal to measuring a gray card at the subject using a spot meter.

Scene: Park with dense foliage.

Medium: Roll film.

I am interested to meter the texture of tree bark which is in shade but also the part of the bark is directly illuminated by the Sun.

To record the adequate shadow detail, I incident meter the shadowed bark with meter's dome pointing towards the camera. This gives me the base exposure.

Since, I am shooting only with roll film the highlight reading is not so interesting in this scenario.

Confusion: After reading BTZS, it said there is a discrepency between what the dome of incident meter measures to what the dial does with the measurement.

Question: Do modern meters have this discrepency too? Now, I own a Gossen Digisix and wonder whether I need a correction for the shadow and highlight as described in BTZS?

[Ken Lee]

If you expose based only on the highlight reading, the shadows may be underexposed, depending on the brightness range of the scene.

A standard 18% gray card is 1/2 stop too light. 100% -> 50% -> 25% -> 12.5%, not 18%. If you meter a gray card with a spot meter, place it on Zone 5.5, not 5. Either that, or shoot your film at 1/2 stop lower speed. For example, Ansel shot Tri-X at 250, and so did Fred Picker, and so did I in the 1970s. Because we used an 18% gray card. Had we used a 12.5% card, we might have ended up shooting at 400 or very close to it.

The BTZS book requires multiple reads. Note that they always expose based on the shadow reading, not the highlight reading. With roll film, you hope that your scenes aren't too contrasty, but you make sure you have adequate shadow detail because if you underexpose, it won't get onto the film.

[baachitraka]

Sorry, I was not clear on where I want to meter to establish the base exposure. Indeed, I will take the shadowed bark reading with meter's dome pointing towards the camera.

I have understood a bit about gray cards after reading BTZS.

For a normal 7 stop range it is 9%, one full stop lighter. Practically this range is limited by lens flare and the camera so the effective range shortens to 6 stops.

The mid-point of six stop is 0.9 in log scale which can be translated to 12.5% in terms of reflectance.

Nevertheless, I'm still figuring out this discrepency as mentioned in that book, between the dome and the dial. I am too confused with this.

[Ken Lee]

I never understood that discrepancy either, and have brushed it aside with no ill-effects. In the BTZS books, I ultimately refer to the section which shows people metering and exposing their film. In particular, there is a photo of a fellow shooting a barn, which is etched in my memory. I just follow those "instructions".

If we shoot roll-film with a wide variety of Subject Brightness Ranges, then a developer like Divided Pyrocat can be helpful since it develops all exposures to the same basic contrast index. If we shoot a roll-film camera with interchangeable backs, then we can dedicate each roll to a different SBR if we like, and then expose/develop the roll accordingly.

[baachitraka]

I see the magic of Pyro et al in your gallery.

Okay, I will shoot without worrying much about the discrepancy. Finally I am relieved.

[baachitraka]

http://www.largeformatphotography.in...at-Light/page2

Please refer to sanking comments.

[Leigh]

A standard 18% gray card is 1/2 stop too light. 100% -> 50% -> 25% -> 12.5%, not 18%.

An 18% gray card is 2.5 stops down, not 3 stops. This puts it in the middle of the 5-stop "adequate detail" range.

Adding one stop at each end, for "very black" and "very white", yields a conventional seven-stop exposure range.

- Leigh

NB: -2.5 stops is actually 17.67766953 % but we call it 18% because the real number is too long to recite.

[Mark Barendt]

Confusion: After reading BTZS, it said there is a discrepency between what the dome of incident meter measures to what the dial does with the measurement.

Got proof?

Question: Do modern meters have this discrepency too? Now, I own a Gossen Digisix and wonder whether I need a correction for the shadow and highlight as described in BTZS?

Have you actually matched this against film?

-------

Incident metering doesn't match a gray card per se, but the two styles of metering can be used interchangeably. A gray card (or white, black, flesh, denim, or .... ) simply provides a reference point that can be "known"; calibrated to a film.

Film testing or ISO standards provide the calibration.

[Leigh]

If your gray card differs significantly from an incident reading, you're not using the card correctly.

The card is supposed to be set at an angle such that a line drawn perpendicular to its surface
will bisect the angle formed by the incident light and the lens axis.

Pointed at any other angle it will not give the intended 18% reflectance.

- Leigh

[Shen45]

Hi baachitraka, are you actually using the BTZS [system] as intended - full paper test and full film test and exposure carried out based on the data provide and then the film developed as per the tests conducted with your film developer combination that has been exposed to the recommended camera settings using either a spot or incident meter? If not you are very much trying to ram a hexagonal peg into non existent round hole. It may be Mark that has information on a book using 2 incident readings in general photography and that could be very helpful to you but you cannot pick and choose info from BTZS and expect much more than confusion. The book Mark suggests may initially offer more help. BTZS is not confusing in the least. It does however have a steep initial learning curve as you jettison many old habits.

When metering with digital incident meters they must in most cases be set to 100 iso to give correct EV readings.

If none of what I have written is applicable please ignore.