Question about metering colour slides

David A. Goldfarb · Mar 3, 2012

An incident reading will work for a lot of normal subjects without a very wide brightness range.

The underlying principle of exposure in the zone system is actually the same for negative or reversal film: expose for the value that represents the minimum density on film.

So with negative film expose for the shadows; with reversal film expose for the highlights.

I do some bird photography, and if I'm photographing a white bird, then I'll spot meter the white feathers and open up 1-1/3 stops from what the meter considers a middle grey, because that's as bright as a film like Provia 100F will let me get it before blowing out the highlights, and the shadows will fall where they may.

If it's mid-day and the sun is high in the sky, I'll probably just take a break and have lunch, because the light is too contrasty for bird photography with slide film, unless I've brought a flash to balance the harsh light from the sun and fill shadows from branches and such.

If you don't spot meter and only have the incident meter, then you have to be a bit more conscious to compensate for bright white subjects and experiment to see how much you need to stop down with the film you're using in those situations.

Also, bracket. You may find that there's a range of "correct" exposures +/- 2/3 of a stop, and it depends on what you want to emphasize, and you won't know what's best until you've got the slides on the light table in front of you.

markbarendt · Mar 3, 2012

EASmithV said:
Reading this really enlightens me with how bad I am with metering... I usually just roll with whatever my meter gives me, or take 3 readings in the dark/mid/light zones of the image area and average them.

I'm not quite sure I understand the advantages of duplexing... I set up a test subject and using the method discussed earlier to meter, my readings agree with what my matrix meter in camera is telling me to use anyway.

It's not a surprise that a matrix meter would agree with duplexing for many shots. The goal of each is the same.

The difference is that incident metering doesn't easily get fooled by changes in scene reflectivity. A white wedding on a ski slope is easy with duplexed incident metering, it takes a bit more thought with reflective meters.

I said this before but it bears repeating, setting exposure is a compromise between the needs of competing subjects.

Duplexing measures two things.

1-A Highlight peg. Meter pointed straight at the light source.

2-A Mid-tone peg. Meter pointed toward the camera, hopefully parralel to lens axis.

The highlight peg used by itself, in theory should protect against almost all overexposure. This isn't like a spot meter reading though, even pointed at the sun this is essentially measuring something close to what would be used for a "front lit" exposure value. For a front lit photo you could almost stop here, as the light swings around your subject though stuff facing the camera can start to go into silhouette. If that's your intent, great; if not you need to adjust.

In terms or light swinging around your subject think Lahaina Noon, in Hawaii the sun reaches a point during the year where when standing upright at noon you don't cast a shadow except on your own feet. At Lahaina Noon, if someone is wearing a wide brimmed sun hat they can be fully lit as if they are in open shade, but their hat and surroundings are in full sun.

The mid-tone peg used by itself, in theory, will place subjects that are facing the camera at normal brightness levels. For example, faces looking at the camera will fall at a "normal" brightness level. This reading by itself doesn't consider the background or the main light.

Duplexing averages these two pegs together.

In the Lahaina Noon situation the mid-tone peg taken at the subjects nose, under their hat will try to protect detail and brightness in their face and clothing. The highlight peg will try to protect details in the clouds and on top of the hat.

Averaging the two readings is simply a recognition of the reality that we have to compromise. Duplexing provides a very reliable compromise.

The only way to avoid an exposure compromise like this example at Lahaina Noon with a subject under a big hat is to use artificial lighting, reflectors, speed lights, table lamps, movie lights, or whatever to light the subject to your preference.

mark · Mar 3, 2012

I have a love hate relationship with transparency film: I love it and it seems to hate me these days. Metering it can be difficult. When in doubt or in unrepeatable situations BRACKET.

Here is what I was taught to do if you wanted to get good consistent shots
1-Practice in different lighting situations - Dawn, Morning, Mid day, evening, dusk and different subjects
2-Bracket all of those shots
3-Write notes after all bracketing is done
4-develope film but have it sleeved not put into slide mounts
5-Cut the three to five bracketed shots so they are all together
6-Using a GOOD light table examine them and write notes about each exposure on the same page you wrote the exposure info

Of course this was done when film was cheap. It is not anymore but this helped me a lot. I could incident meter something and know from my studies what to do to get what I wanted. Hope this helps.

I should probably do this exercise again to get over the hump I am climbing.

benjiboy · Mar 3, 2012

markbarendt said:
It's not a surprise that a matrix meter would agree with duplexing for many shots. The goal of each is the same.

The difference is that incident metering doesn't easily get fooled by changes in scene reflectivity. A white wedding on a ski slope is easy with duplexed incident metering, it takes a bit more thought with reflective meters.

I said this before but it bears repeating, setting exposure is a compromise between the needs of competing subjects.

Duplexing measures two things.

1-A Highlight peg. Meter pointed straight at the light source.

2-A Mid-tone peg. Meter pointed toward the camera, hopefully parralel to lens axis.

The highlight peg used by itself, in theory should protect against almost all overexposure. This isn't like a spot meter reading though, even pointed at the sun this is essentially measuring something close to what would be used for a "front lit" exposure value. For a front lit photo you could almost stop here, as the light swings around your subject though stuff facing the camera can start to go into silhouette. If that's your intent, great; if not you need to adjust.

In terms or light swinging around your subject think Lahaina Noon, in Hawaii the sun reaches a point during the year where when standing upright at noon you don't cast a shadow except on your own feet. At Lahaina Noon, if someone is wearing a wide brimmed sun hat they can be fully lit as if they are in open shade, but their hat and surroundings are in full sun.

The mid-tone peg used by itself, in theory, will place subjects that are facing the camera at normal brightness levels. For example, faces looking at the camera will fall at a "normal" brightness level. This reading by itself doesn't consider the background or the main light.

Duplexing averages these two pegs together.

In the Lahaina Noon situation the mid-tone peg taken at the subjects nose, under their hat will try to protect detail and brightness in their face and clothing. The highlight peg will try to protect details in the clouds and on top of the hat.

Averaging the two readings is simply a recognition of the reality that we have to compromise. Duplexing provides a very reliable compromise.

The only way to avoid an exposure compromise like this example at Lahaina Noon with a subject under a big hat is to use artificial lighting, reflectors, speed lights, table lamps, movie lights, or whatever to light the subject to your preference.

Marks remarks agree with my experience of using The Duplex Method of metering since I first read about it in The Exposure Manual by Dunn and Wakefield about thirty years ago and I have used it since then, it's very simple to use, and I find it produces a higher proportion of acceptable/correct exposures for me on slide film than any other method.

Question about metering colour slides

David A. Goldfarb

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markbarendt

mark

benjiboy

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