Incident metering

[arie_haziza]

Good morning,

 

I received several anwsers to the following question, and I would

like to hear from those of you who have experience with incident

metering with B&W negative films:

 

Once I take the incident reading, do I need to alter the measure if

I use B&W negative film for ceratin types of subjects?

 

Some people said no, some said yes, so I am kind of lost. Some have

said that incident metering does not need adjustment if using slide

films. But with B&W negative film, we need to adjust for certain

situations.

 

I would appreciate your help.

 

Thanks

[SCL]

Incident metering reads the amount of light falling on the subject - and therefore is independent of the subject, or the film type. In theory all ranges of tonality encompassed by the film for the amount of light falling on the subject should be accounted for in the reading. However, if you are thinking in Zone System terms, and wish to shift the tonality of an object, of course you will want to alter the reading. It isn't the type of subject or film, as you suggested, but rather the tones you wish to impart to the subject, knowing the amount of light shed on the subject.

[arie_haziza]

that's was my understanding too, but various people have said otherwise for very specific situations: for subjects that are very dark or very light, they suggested an adjustment. That is why I am a little bit confused (I thought that teh idea of incident metering who spare us of the need to adjust the cell reading)

[gsmith]

You can think of incident metering as giving you a similar result to reflected or spot-

metering an 18% gray card in the same light as your subject. All else being equal, the

exposure information for the two methods should be the same.

 

That is, the % reflectance of the subject is essentially irrelevant when using incident

metering. If you put a gray card in front of a bright white object and get the correct

exposure with a reflected light meter, there would be no need to account for the meter

trying to make the bright white subject into 18% gray (e.g. opening up 1-2 stops). Same

goes for unusually dark subjects.

 

However, if you tend to favor a slight over exposure of, say, half a stop (as many do

specifically with B&W film to get good shadow detail), then you would need to make a

correction. Also at extreme EVs (very dark or very light) you would need to take

reciprocity failure into account. But, for the majority of cases, a good incident reading

(taken close up, without you or anything else occluding the subject) will give you the

correct exposure for zone V, allowing the other values to fall into place.

[tony_senzaorbi]

I've seen the same difference of opinion on net forums, so unless you are either going to tally the answers and go with the majority, or have certain people you are willing to blindly trust, you might have to try a roll with different subjects and see for yourself. I currently work with a pro for weddings on weekends and evenings, and have worked for others before and in the studio as well as on location for ad brochures. All the pros I've worked with over the last 15 or more years use the in-camera meter 95% of the time, the remaining 5% is incident metering but only for flash. Experience teaches how many stops away from neutral a subject is, and you compensate the reflected reading that much. Really bone simple. Incident meters measure the light incoming on a subject with the assumption that most or all of it will be reflected into the lens. So incident readings are generally free of need to compensate for all subjects other than those that are non-reflective: very dark ones, especially those with matte surfaces.

[frederick_muller]

Stephen's answer reflects (no pun intended) most of my understanding of the matter. The one point on which I would disagree regards the statement that the incident reading is meant to capture the full range of tonality that the film captures. The interplay is between the tonal range that can be captured by the film and the tonal range inherent in the scene. If the tonal range inherent in the scene is broader than the tonal range that the film can capture, you will have to decide whether to let the shadows or the highlights go and modify your exposure accordingly. In that case, a reflected light meter, with the ability to measure contrast range, is helpful.

[guy bennett]

"...various people have said otherwise for very specific situations: for subjects that are very dark or very light, they suggested an adjustment."

 

It sounds like these people were thinking of reflected, not incident, light readings, in which you should adjust the exposure indicated by the meter in the above cases to avoid over or under exposure.

 

As Stephen Lewis mentioned above, incident metering reads the light falling on the subject -- not reflected by it -- and thus shouldn't be influenced by the light or dark tones of the subject itself. The exposure indicated by incident metering should give you correctly exposed negatives.

 

If you'd like to experiment with that exposure, why not shoot a roll and bracket each shot, using 1/2 and/or 1 stop more and less light than the incident reading suggests, then you can see the results for yourself.

[huw_finney]

The correct exposure for a negative film is the absolute minimum required to give detail in the darkest part of the subject where detail is wanted, the highlights are adjusted by development time. However in the real world and with modern films an incident reading will give a printable negative nearly all of the time. Take a look at the SEI user manual (there is a copy on my website, huws.org.uk) this is explained there.

[ronald_moravec1]

Once you establish that your shutter and F stops on your camera are adjusted ( personel film speed), give you a good exposure with sun over your shoulder scene, adjust for filter factors and bellows extension only.

[david j.lee]

try to get a copy of "the black and white handbook" by fellow leica forum

member roger hicks and his wife, frances shultz. they cover this issue and a

lot more there.

[jonathan_reynolds]

I found some of the contributions to <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00BlFC" target="_blank">this thread</a> helpful. Shattered a false conception I had about incident metering. From the views above, looks like it's a common misconception.

[rdkirk]

I'd go mostly with Frederick. Although the incident meter isn't influenced by the tonality of the scene, the limitations of the film/camera/processing system may yet require compensatory measures to capture the portion of the scene's dynamic range that the photographer is concerned with.

The incident reading should capature the center of the range properly, but I might be more concerned with what's going on in the highlights in a scene of polar bears on snow, or what's going on in the shadows of a scene with a black cat on a porch during a sunny day. In that case, I'll need to bias the incident reading in one direction or another and compensate in processing and printing--or change the light ratio of the scene when I take the picture.

 

At this point, the incident light meter leaves the photographer guessing or running on experience, where the reflected light spot meter would provide additional real information about the actual dynamic range of the scene.

[george_b1]

Quoting from the National Geographic Field Guide: Incident Light Exposure Meters. Page 148

 

". . . In some situations, you may need to deviate from an incident meter's recommended settings. With a bright subject (like snow) decrease exposure slightly to retain texture. With a dark subject - such as a black cat in shadow - increase exposure slightly. This is contrary to the reflected exposure metering technique, but is correct with an incident meter."