BTZS: Incident Readings in Flat Light

[Ken Lee]

Let's say we are shooting where there are no apparent shadows. With an incident meter, how do we meter the scene? Do we simply presume that the SBR is 7, and take only one reading, "the" reading ? Do we adjust exposure, or just use the reading as-is ?

[vinny]

That's how i'd do it.

[E. von Hoegh]

Let's say we are shooting where there are no apparent shadows. With an incident meter, how do we meter the scene? Do we simply presume that the SBR is 7, and take only one reading, "the" reading ? Do we adjust exposure, or just use the reading as-is ?

Flat light, no apparent shadows, and I'm assuming B&W film, I'd just meter and use the reading with no correction. Hard to go wrong, actually.

[Jay DeFehr]

Ken,

I generally consider flat/ no shadows light to be less than SBR 7-- more like SBR 5. In this case I know I can give less exposure because I will develop more than normal to expand mid tones. If I'm using TMY-2 and processing in 510-Pyro, I'll expose at EI 800 under these conditions. below is an example of just this scenario. the scan isn't great, but it prints very nicely on G2 paper.

[IMG] Untitled by Jay DeFehr, on Flickr[/IMG]

[Ken Lee]

In shots like that one, there is a light source overhead, albeit a very large one: the sky. There are some slight shadows: there is some shading, because we see creases in the clothing, and the neck is somewhat darker than the face.

But that being said, you're right ! I forgot that a flat scene has an SBR of 5, and usually requires some expansion to look nice on film, because 7 is considered normal, not 5.... I think :-)

This is all new to me, pardon my confusion.

If we are using roll film with a divided developer, where we only need to place the shadows (and allow the developer to handle the high values), what do we do if there are no shadows per se ? In that case, would it be fair to say that the SBR is so low that we don't care ? Just meter the scene ?

[BetterSense]

I basically consider an incident meter's recommendation a guideline for how to expose transparency without blowing out any highlights. When I use an incident meter with negative film in normal-to-contrasty light, I routinely expose a stop or two (or more) over the meter's recommendation.

When it's gloomy out, and if I had an incident meter, I would take an incident reading and expose to the meter recommendation, if doing so wasn't too much trouble given the amount of light. So this amounts to "a stop less than normal if it's gloomy".

[mdm]

What about improvising the shadow reading, for example turn you back to the general direction of the light and meter your shadow. I am a long way from being an expert but thats what I do fairly often. In BTZS exposure is based on a shadow reading and the iso of your meter is set to roughly double what you would otherwise expect to compensate, and if you err on the side of too deep a shadow, at least you are not underexposing. Though it does say in the book beginners tend to err on the side of too dark a shadow.

[Jay DeFehr]

In shots like that one, there is a light source overhead, albeit a very large one: the sky. There are some slight shadows: there is some shading, because we see creases in the clothing, and the neck is somewhat darker than the face.

But that being said, you're right ! I forgot that a flat scene has an SBR of 5, and usually requires some expansion to look nice on film, because 7 is considered normal, not 5.... I think :-)

This is all new to me, pardon my confusion.

If we are using roll film with a divided developer, where we only need to place the shadows (and allow the developer to handle the high values), what do we do if there are no shadows per se ? In that case, would it be fair to say that the SBR is so low that we don't care ? Just meter the scene ?

Ken,

I suppose it depends on what we mean by "divided developer". If you're referring to something like DD23, I call these type A 2-bath developers because development begins in the first bath, and allows for development controls. Type B 2-bath developers, like a 2-bath version of Pyrocat HD, in which no development takes place in the first bath, do not allow development controls. With these developers we expose for the shadows, and develop. In short, type B 2-bath developers are not compatible with ZS or BTZS methods.

Whatever developer we're using, in flat, SBR-5 light, there's not enough difference between the shadows and highlights to bother with multiple readings, in my opinion. If you're using a type A 2-bath developer, you can adjust your EI to your development, and in that case, if you want a very accurate measurement of your SBR, you should take two readings, but if I'm reading you correctly, you're asking about roll film exposed under various light conditions, in which case development controls and related exposure adjustments are not appropriate, and a single incident reading at box speed is perfectly adequate.

[sanking]

Let's say we are shooting where there are no apparent shadows. With an incident meter, how do we meter the scene? Do we simply presume that the SBR is 7, and take only one reading, "the" reading ? Do we adjust exposure, or just use the reading as-is ?

With BTZS technique the assumption is that a scene that has completely flat lighting will have an effective SBR of 5. So to determine the SBR of any scene take one reading in the shadows (dome of meter facing the camera) where you want to have detail and record the EV, take a second reading (again, dome of meter facing the camera) in the most brightly lit area of the scene and record the EV. Subtract the first EV reading from the second reading, and add the result to 5. This will give you your effective SBR. For example, if your first incident reading in the shadows is 13.0, and your second reading in the bright area of the scene is 15.0, the EV difference is 2, so add this to 5 to get a SBR of 7. Your exposure would be based on the first reading in the shadows, your development on the SBR, and if you use BTZS you would have done film tests in advance to know how to develop for any given SBR.

Negatives exposed in scenes of normal and low SBR are best handled by traditional one-bath developers. Scenes of high contrast can also be handled with reduced development time, or weaker developer dilutions. My experience is that scenes of very high contrast (SBR of 11 or more) are best handled by two-bath development, where the first bath contains the reducer, the second bath contains the alkaline accelerator. Diafine is a commercial developer that can be used for this application, and you have seen the threads on the use of Pyrocat-HD as a two-bath developer.

One of the major goals of BTZS field use is to determine the SBR of the scene, and this in turns determines the type of development required.

Sandy

[ic-racer]

How did you calibrate the meter. If it is calibrated so that the lowest value in the negative that will print with detail is 3 stops below the indicated exposure then it will be a good exposure. If the meter is calibrated so that the lowest value in the negative that will print with detail is 5 stops below the indicated exposure, you will still get a printable negative but it will be more dense and some of you exposure latitude (for error in exposure/lens/shutter) is used up as the high portions get closer to the shoulder.