B&W exposure latitude

[andrew.roos]

fralexis, I'm essentially doing what you suggest. I don't have a separate meter so I use my DSLR's spot meter for landscapes. When shutter speed permits, I follow Barnbaum's (The Art of Photography) recommendation of placing the shadows where I want detail into Zone IV at box speed - equivalent to placing them into Zone III at half box speed. This gives me some protection against under-exposure and has essentially no disadvantages since the film I use (Delta 100) has at least 2 stops more latitude for over-exposure than for under exposure (based on the characteristic curve measured by Michael R 1974) before hitting the shoulder. By over-exposing by one stop, I'm really just placing middle grey in the middle of the straight-line section of the curve, with about 4 stops dynamic range in both directions (8 stops total) before hitting the toe or shoulder. The shoulder is much more gradual than the toe so there is still some latitude for (even more) over-exposure. At the sizes I print, the grain from Delta 100 is negligible anyway, so I don't worry about the slight increase in grain from over exposure. Shadows blocking from under-exposure would be much more problematic. But note that I'm new to analog, so judge what I say accordingly.

[markbarendt]

Using an incident meter still requires to remember that with slides you expose "for the highlights" and with negatives you expose "for the shadows" when you have a scene in front of you with both zones in bright sun and zones in the shade.

I was lucky enough to find and read Dunn & Wakefield's Exposure Manual a while back. It gives various scenarios and the reasons for using various types of metering in them. Great text for anyone trying to figure out how to meter better, out of print but normally available used, I'd recommend the 3rd or 4th edition.

They actually recommend duplexed incident metering for slides, one traditional reading (mid-tone) is averaged with a light source (highlight) reading. I actually use this method for almost every shot I take and have yet to be disappointed at either end of the scale. Traditional incident metering (dome out) works just as well for front and side lit subjects, duplexing (flat faced/dome in) gains an advantage when the main subject is backlit.

BTZS pegs from the shadow incident reading and factors in a variety of other considerations including highlights similarly in theory to the Zone System. Both of these methods generally seek the minimum exposure which is a reasonable goal.

When I worked Zoning and Duplexed Incident side by side I found that there was normally little if any difference in the camera setting found, when there was a significant difference I'd recheck the the "zone" reading based off what the incident meter had told me and find where the incident meter was trying to put the shadow. Almost every single time I did this I found that the shadow placement was normally very acceptable to me.

[Steve Smith]

I was lucky enough to find and read Dunn & Wakefield's Exposure Manual a while back.

I bought a copy of that last year.

They actually recommend duplexed incident metering for slides, one traditional reading (mid-tone) is averaged with a light source (highlight) reading.

And mentioned that in the similar thread we had at the time!!

Basically, it's using the incident meter at the subject and taking one reading pointing at the camera and one pointing at the light source and going half way between the two.

This only applies to incident meters with flat diffusers (if I remember correctly) as domed diffusers already take this into account by design.


Steve.

[markbarendt]

Yep, exactly Steve.

[RalphLambrecht]

bxxxxxxxxxxb&wfilm is ver orgiving in tems of over exposurebut has little lstitude in terms of under exposure

[RalphLambrecht]

andre,
welcome to analog. your method seems very sensible to me!

[Bill Burk]

fralexis,

You are getting good, sometimes conflicting advice. Your interpretation of Ralph's charts on post #21... that it is OK to rate at half box speed... is a simple and effective way to assure adequate shadow detail and ease of printing.

More precise metering can provide you "better" negatives. Better being relative. Less grain (which today is not a common goal of analog photographers). Shorter, or more consistent print exposure times (which can make darkroom work more productive, again not a common goal today).

I use a 4x5 rangefinder which sometimes requires me to use full rated speed when handheld. But when I shoot landscape, I do not need the highest film speed because I am using a tripod and I love the aesthetic of water at slow shutter speeds.

[andrew.roos]

andre,
welcome to analog. your method seems very sensible to me!

Thanks Ralph!

And thanks for the very informative illustrations you posted, especially the one showing the same scene photographed with over- and underexposure. It makes the point very effectively.

[seadrive]

Another way to look at this is that your exposure latitude is a function of two things:

1) the contrast of the scene you are photographing; and
2) how many effective contrast grades of paper you have available to you.

At one end of the spectrum, let's say you are photographing a subject that has both whites and blacks that you want to render realistically, and that the white value is in sun, and the black value is in shade. Let's also assume that you are going to make a contact print, and that you have exactly one grade of paper (#2) and one developer (Dektol).

In this situation, you have very little latitude for error, either in exposure or development, because you need to render a full tonal scale, and the only tools you have available to you are, ummm... exposure and development. The difference between the low value in shade and the high value in sun is about 8 stops.

If you underexpose the negative, you'll lose important shadow detail just above pure black, and if you overexpose or overdevelop, you'll blow out your high values, and they'll be rendered without any tone or detail.

Now let's change the situation. The scene is the same, but it's now overcast, not sunny. The difference between black and white is now only about 5 stops. Furthermore, you're using a variable-contrast paper, and you have filters that get you from grade #0 to grade #5, and everything in between. On top of that, you have both Dektol and Selectol-Soft (or a Beers developer) that can also adjust the contrast grade of the paper you're using.

In this situation, you have a ton of latitude! Assuming you give the scene enough exposure to get the low values above film-base-plus-fog, you can be off up to three stops in exposure (or the equivalent in over-development), and still get a printable negative. The contrast of your scene is much smaller than your effective contrast grades in printing paper (effective = actual paper grades +/- those attained with soft/hard developers), so you can take your scene's tonal scale, and move it all over the place, or expand and contract it at will.

I agree with everyone else that, whatever latitude you have, it's on the "high" side. If you underexpose the negative, and there are "low" values in the scene that are important, then you're SOOL. If you overexpose the negative, then it mostly depends on the range of the important values in the scene.

It's for this reason (and the decline in the ability of modern films and papers to separate the low values in the scene from each other) that Fred Picker, late in his career, changed the way he determined proper exposure. Rather than expose for the low values and develop for the high values, he said "Place the highest important value on Zone VIII, and expose." That exposure placed the low values in the scene as high up on the scale as they could go, and he could then use the other tools at his disposal (mostly paper grades) to place the low values where he wanted them in the print.

[Michael R 1974]

A wrench I'd like to throw in is that development affects the film's effective exposure latitude. For example, when dealing with very high contrast subjects (and this is one of the serious flaws in Barnbaum's book), given a fixed subject brightness range, exposure latitude decreases as development is reduced, due to shouldering effects.

This runs counter to the way we typically think about development in the context of the zone system. It could be called "zone system failure". The standard zone system formula assumes the shape of the film curve remains essentially constant, and that development modifications shift the curve and/or rotate it. This is valid within a certain density range, but begins to break down when the subject brightness range is long enough to indicate significant or severe contractions.