Underexposure with incident metering

[Spanik]

... all a meter does is measure the light and that isn't necessarily the same as the correct exposure.

Yes, it is a correct exposure. Maybe not an artfull/creative exposure, but it is the one that will give a technically correct exposure that will place a thus exposed 18% grey right in the middle of the curve of your film. That is how the whole thing is defined in the first place: lightmetering, iso sensitivity etc.

As for the sun always being the same... 1 stop between februari and april, another in januari. And that is only for a single lattitude.

 

[Roger Hicks]

... all a meter does is measure the light and that isn't necessarily the same as the correct exposure. A meter can give one a baseline to work from but its up to the photographer to think through the correct exposure.

For photographic purposes full sunlight is the same year round and in any location I've ever visited, so I would not use a meter when the sun was out ... I'd just decide how much I needed to adjust from f16 1/film-speed to get the negative I wanted

Dear Stewart,

Your lack of precision is covered up to a considerable extent by the inherent flexibility of pos/neg photography. Sunlight is most assuredly not the same the world over, and there is plenty of research to confirm this.

In the 1990s the Japanese representatives on the ISO film speed committee wanted the slope of the ISO standard d/log E curve reduced from about 0.62 to about (as far as I recall) about 0.56 to allow for the fact that the light in Japan is clearer and contrastier than in Rochester, NY, the original home of what became ASA and then ISO.

For a more primitive demonstration of similar facts, take a look at any exposure calculator, the old slide-rule type where you dialed in countless variables. Latitude was one of them.

You are simply reasserting the undoubted truth that you know how to fudge straightforward readings.

Cheers,

R.

 

[Roger Hicks]

Yes, it is a correct exposure. Maybe not an artfull/creative exposure, but it is the one that will give a technically correct exposure that will place a thus exposed 18% grey right in the middle of the curve of your film. That is how the whole thing is defined in the first place: lightmetering, iso sensitivity etc.

No, no, no, and no.

First, no film speed is based on mid-tones. Neg film speeds are based on shadow detail and slide film speeds are based on highlight detail.

Second, no, a mid-tone isn't "in the middle of the curve of your film." There's normally lots more useful information, well above whatever you record on the film as a mid-tone, unless you grievously over-expose.

Third, no, 18% is only a mid tone if you look at a long sequence of grey cards from very light to very dark. Most people will pick about an 18% grey as a mid tone, but this has little or nothing to do with the representation of a "mid tone" in a photograph.

Fourth and finally, there is no such thing as a "correct" exposure. There is only a pleasing exposure.

Exposure and ISO speeds are all based on "psychophysics" (what looks right), and on a few useful generalizations: that most outdoor scenes reflect about 12-14% of the light falling on them (not 18% -- look up the original research, not the Zonie creed); that brightness ranges for important tones are often less than 256:1 under absolutely uniform lighting (and the lighting in a cave is not the same as the lighting falling on its mouth, nor is the light in the corner of a room the same as the light beside the window); and that flare levels in old lenses generally would reduce 256:1 to 128:1, allowing a reasonably 1:1 tonal representation in a print with only modest further compression. None of these generalizations is invariably true.

Cheers,

R.

 

[Juan Valdenebro]

Dear Juan,

Consider the shape of a d/log E curve, and the fact that both the slope and to a lesser extent the shape of the curve can be changed. Then consider the simple truth that if a print has a brightness range of 2.1 -- seven stops -- you're doing very well indeed. In other words you're compressing the brightness range of the real world immensely: a sunny scene can easily top 10 stops. And you're not compressing it linearly. In other words you can, depending on your intention and your skill, record more or less of the shadows in any print. That's before you start dodging and burning...

Now consider that the old name for incident metering was the "artificial highlight" system, because that's exactly what it is: the meter reading is based on the brightest highlight you can record without "blowing", i.e. the meter reading is keyed to the highlights. ISO speeds for negative film are based on the minimum exposure required to give texture on the film, i.e. they are keyed to the shadows.

A grey card is about 2.5 stops darker than the "artificial highlight". That's how it's defined: 18% reflectance, whereas a pure white is about 90%. A moment's thought reveals that a grey card is therefore keyed to the highlights, and that any shadow much darker than about 3-4 stops down from the grey card will have no detail. Often, shadows are a good deal darker than 3-4 stops down. Unless you read these shadows directly, you cannot guarantee adequate exposure.

In other words, you could read a sheet of white paper; or a sheet of grey paper; or the inside of an incident light receptor; and they should all give you the same reading, after you've adjusted for the reflectivity of the paper or the translucency of the incident light receptor (different index marks on the meter for spot, auto-compensated by the density of the incident light receptor). But none of those readings will give you detail in shadows much more than about 3-4 stops down from your artificial mid tone. It doesn't matter whether you read the incident light off the white paper, grey paper or incident light receptor: it's all incident light, and it's all keyed to the highlights.

If you don't want shadow detail, fine. But if you don't, why piddle around with taking a reading with an (expensive, inconvenient) spot meter and an even more inconvenient grey card instead of an incident light reading?

Of course "Direct sun can sometimes cause wrong incident metering" but so can incompetent positioning of a grey card. My argument is that it's just as easy to learn to use an incident light meter competently, and a lot easier to actually use it. And you will get exactly the same reading both ways.

If you prefer to use a spot meter and a grey card, well, that's fine: it works for you. But it's still logically and practically exactly the same as incident light metering.

Cheers,

R.

Hi Roger,
The only ocassion I care seriously about shadow detail is when I shoot a direct sun scene where I need very clear shadows because it's there where the most important facts of my image are happenning, and for all my films I have notes: in that case, generally I expose for close to two stops more light than usual, and develop using a much shorter time... But in 95% of my shooting I get perfect shadows without metering shadows because of a correct light reading...
I prefer to use spot metering only when I judge it's the best way to meter a scene, and I use incident metering and in camera metering all the time too, obviously...
And no, they're not the same thing.
But if you want to consider them logically and practically the same thing, it's OK...
Cheers,
Juan

 

[Roger Hicks]

Hi Roger,
The only ocassion I care seriously about shadow detail is when I shoot a direct sun scene where I need very clear shadows because it's there where the most important facts of my image are happenning, and for all my films I have notes: in that case, generally I expose for close to two stops more light than usual, and develop using a much shorter time... But in 95% of my shooting I get perfect shadows without metering shadows because of a correct light reading...
I prefer to use spot metering only when I judge it's the best way to meter a scene, and I use incident metering and in camera metering all the time too, obviously...
And no, they're not the same thing.
But if you want to consider them logically and practically the same thing, it's OK...
Cheers,
Juan

Dear Juan,

Stop and listen to yourself. You get "correct" light readings -- except when you don't. When you don't you have to fudge by giving 2 stops extra exposure -- which a direct reading of the shadows would have indicated anyway.

Perhaps you would be kind enough to explain the logical and practical differences between:

1 Metering a grey card

2 Metering a piece of white paper and giving 2-1/2 stops less exposure (because the white card reflects 2-1/2 stops more than the grey card)

3 Metering any other artificial highlight, such as an incident light receptor, with the appropriate correction.

It's not that I consider them the same: it's that they are the same, whether you're willing to admit it or not. Either explain the difference, or accept my argument.

Cheers,

R.

 

[shortstop]

Hi Roger,
I read your link on the negative and some of the answers you gave on the forum. my beliefs are changing. do not fully understand some concepts. I think I'll buy your book on the exposure. I'm not sure of one thing: in your opinion, spot metering of the shadows is the best way to make a measurement? Could we simplify by saying that: 1 I measure the shadows I want the detail (zone 2). 2 I open the aperture stop 3. 3 if I have a single negative (or a roll with shots of the same scene) I measure the highlights and develop consequence.

 

[Roger Hicks]

Hi Roger,
I read your link on the negative and some of the answers you gave on the forum. my beliefs are changing. do not fully understand some concepts. I think I'll buy your book on the exposure. I'm not sure of one thing: in your opinion, spot metering of the shadows is the best way to make a measurement? Could we simplify by saying that: 1 I measure the shadows I want the detail (zone 2). 2 I open the aperture stop 3. 3 if I have a single negative (or a roll with shots of the same scene) I measure the highlights and develop consequence.

Close, but step 2 is backwards. If you're using the mid-tone meter index, close down 2-3 stops or you'll get hopeless over-exposure.

Spot metering of the shadows (Zone 2) is the only way to guarantee texture in Zone 2 without fudging, guesswork or willful over-exposure, but most decent spot meters have a "shadow" index. Use this instead of the mid-tone index (substantially useless on a spot meter) and then, as you say, for Step 3, use the highlight index.

If you can get close enough, you can also do this with a non-spot meter: see http://www.rogerandfrances.com/subscription/over-under-indices.html

To be honest, it's all pretty flexible and you can get away with a lot, but at least if you do it in the way I describe you'll be closer to theoretical and practical standards and will need to rely far less on flexibility aka sloppiness.

Cheers,

R.

 

[Sparrow]

Dear Stewart,

Your lack of precision is covered up to a considerable extent by the inherent flexibility of pos/neg photography. Sunlight is most assuredly not the same the world over, and there is plenty of research to confirm this.

In the 1990s the Japanese representatives on the ISO film speed committee wanted the slope of the ISO standard d/log E curve reduced from about 0.62 to about (as far as I recall) about 0.56 to allow for the fact that the light in Japan is clearer and contrastier than in Rochester, NY, the original home of what became ASA and then ISO.

For a more primitive demonstration of similar facts, take a look at any exposure calculator, the old slide-rule type where you dialed in countless variables. Latitude was one of them.

You are simply reasserting the undoubted truth that you know how to fudge straightforward readings.

Cheers,

R.

... well that's as may be, but I've taken a incident reading off a clear sky here in the north of England one day and the following day in Greece and found them to be identical so you'll have to forgive my reluctance to give a fig about the "ISO standard d/log E curve" ... after all would you not agree that latitude is simply another factor for the photographer to consider? ... or perhaps you know of a meter that has a 'latitude' setting?

 

[Sparrow]

Yes, it is a correct exposure. Maybe not an artfull/creative exposure, but it is the one that will give a technically correct exposure that will place a thus exposed 18% grey right in the middle of the curve of your film. That is how the whole thing is defined in the first place: lightmetering, iso sensitivity etc.

As for the sun always being the same... 1 stop between februari and april, another in januari. And that is only for a single lattitude.

I have five negative sleeves on my desk at the moment that confirm you are over complicating the matter 🙂

 

[Spanik]

Got about 30 rolls of combined provia 400x, provia 100f, velvia 50, velvia 100 and ektar 100 that are going to the lab tomorrow (just back from holiday this saturday and the lab is closed on monday). All exposed with incident metering and I know right now which exposures will be wrong because I changed film and not the meter or forgot to account for the center filter on the G617. I do know all the others will be fine.

The only ones that will be a surprise are the stained glass spot metered ones and the sunsets with the G617. The stained glass always is tricky and it was the first time I ever used the G617, don't even know if it works well at all.

 

[Sparrow]

Got about 30 rolls of combined provia 400x, provia 100f, velvia 50, velvia 100 and ektar 100 that are going to the lab tomorrow (just back from holiday this saturday and the lab is closed on monday). All exposed with incident metering and I know right now which exposures will be wrong because I changed film and not the meter or forgot to account for the center filter on the G617. I do know all the others will be fine.

The only ones that will be a surprise are the stained glass spot metered ones and the sunsets with the G617. The stained glass always is tricky and it was the first time I ever used the G617, don't even know if it works well at all.

... well I'll show you mine if you'll show me yours ... 🙂

 

[Spanik]

They aren't that interesting (just ordinary holiday stuff) and I haven't enough webspace. OTOH if any of the G617 are worth posting I'll put them up. But I haven't the faintest idea how to digitalise them. Biggest problem is scanning the lot. I have a backlog of about 20 years to scan. Got a V700 but I never got anything close to what is on a slide to appear on the screen.

(is a different discussion but one of the reasons that make me doubt the viability of film. But I never got a digital photo projected as vibrant as a slide which is something to make you consider the viability of digital)

 

[Gumby]

Dear Stewart,

Your lack of precision ...

Dear Roger, Here I am picking nits and asking a nit-picking question. Mea culpa.

1. Don't you mean accuracy, not precision? 🙂

2. Can you tell us where in history the term "artificial highlight" was used. I am familiar with the dome/disk being an integration instrument and think I understand the intent of the term "artificial highlight", but never heard that anywhere except in your web site. Did Dunn (or someone else) use the term and I glossed over it???

 

[Sparrow]

They aren't that interesting (just ordinary holiday stuff) and I haven't enough webspace. OTOH if any of the G617 are worth posting I'll put them up. But I haven't the faintest idea how to digitalise them. Biggest problem is scanning the lot. I have a backlog of about 20 years to scan. Got a V700 but I never got anything close to what is on a slide to appear on the screen.

(is a different discussion but one of the reasons that make me doubt the viability of film. But I never got a digital photo projected as vibrant as a slide which is something to make you consider the viability of digital)

... yes, same here just snaps from Greece last month ... some of the indoor stuff is a bit thin but I'm content with the result ... I could print almost all of them

Does your meter give you more consistent results?

...

 

[Roger Hicks]

Dear Ed,

(1) No, I mean precision. Of exposure. The meter reading (which is often accurate) is in many cases only tangentially linked to the precision you require in your exposure.

(2) Try The Focal Encyclopedia of Photography, fully revised ed. 1965, vol 2, p 558, several years before I started writing about photography. There are numerous other references but this one, I think, suggests that the term was by then widely accepted.

Cheers,

R.

 

[Roger Hicks]

Dear Stewart,

And?

A lot of adequately exposed images. Which, as far as I recall, you admit you fudged on the basis of experience.

What does this prove, except that you are quite good at fudging?

Cheers,

R.

 

[Sparrow]

Dear Stewart,

And?

A lot of adequately exposed images. Which, as far as I recall, you admit you fudged on the basis of experience.

What does this prove, except that you are quite good at fudging?

Cheers,

R.

... I'd have said reasoned myself ... one could apply 'fudged' any real world method, there is no precision outside density testing in a lab ... oh, and it proves I don't overexpose film in strong sunlight like the OP is having a problem with 🙂

 

[Roger Hicks]

... I'd have said reasoned myself ... one could apply 'fudged' any real world method, there is no precision outside density testing in a lab ... oh, and it proves I don't overexpose film in strong sunlight like the OP is having a problem with 🙂

Dear Stewart,

Ummmm... Underexposing? Given the title of the thread?

Sure, ANY metering method can be fudged in the real world, with enough experience, and even those who are really bad at fudging will often get away with it, given the inherent flexibility of the pos/neg process.

What I don't understand -- and what we see quite often in exposure threads -- is being proud of ignorance. You're not doing that but you are relying to a great extent on flexibility: as in your indefensible statement that sunlight is the same everywhere.

Cheers,

R.

 

[Sparrow]

Dear Stewart,

Ummmm... Underexposing? Given the title of the thread?

Sure, ANY metering method can be fudged in the real world, with enough experience, and even those who are really bad at fudging will often get away with it, given the inherent flexibility of the pos/neg process.

What I don't understand -- and what we see quite often in exposure threads -- is being proud of ignorance. You're not doing that but you are relying to a great extent on flexibility: as in your indefensible statement that sunlight is the same everywhere.

Cheers,

R.

... well if that's your definition of fudging then yes it's a fudge, but then by that definition surely any method one uses with roll-film is a fudge isn't it?

I'm not claiming to be expert and don't think I'm that ignorant, well not in this respect anyway, but any method requires the photographer to simply follow a meter reading is bound to fail under some conditions ... I still contend that any meter-reading needs to have reason applied to it if one is looking for consistent negatives

Sunlight: in my defence I have been using the same meter for over twenty years now and when I've pointed its invacone (as I know it) at a clear sunny sky wherever I've been in the world I get the same reading within a fraction of a stop, what have you found?

 

[Roger Hicks]

... well if that's your definition of fudging then yes it's a fudge, but then by that definition surely any method one uses with roll-film is a fudge isn't it?

I'm not claiming to be expert and don't think I'm that ignorant, well not in this respect anyway, but any method requires the photographer to simply follow a meter reading is bound to fail under some conditions ... I still contend that any meter-reading needs to have reason applied to it if one is looking for consistent negatives

Sunlight: in my defence I have been using the same meter for over twenty years now and when I've pointed its invacone (as I know it) at a clear sunny sky wherever I've been in the world I get the same reading within a fraction of a stop, what have you found?

Dear Stewart,

Highlight 1: How and when is a direct reading of shadows, using the shadow index, going to fail to give adequate shadow detail?

Highlight 2: You know, I've never bothered to write down my meter readings. Why would I? In any case, pointing an Invercone at a clear sunny sky seems an eccentric way to take a reading: it doesn't match any advice I've ever seen on using incident light meters. My incident-light readings are influenced by the time of day; the latitude; whether the subject is front-lit or back-lit; and whether I'm using an Invercone (a particularly brilliant design), an incident light dome, or a flat receptor.

If your idea of an incident light reading is pointing an Invercone at a clear sunny sky, then indeed you must indeed need to do a great deal of fudging/interpreting of the readings.

Cheers,

R.