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EyV Part 4: The language of light

Page 2 - Exercise 4.1

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Project 1, Exposure - Exc 4.1 - Project 2, Layered, complex and mysterious... - Exc 4.2 - Project 3, The beauty of artificial light - Exc 4.3 - Project 4, Ex nihilo - Exc 4.4 - Creativity - Exc 4.5 - Asg 4 Languages of Light

Exercises - Time lapse 1 - Time lapse 2 - Close-ups - The Can

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Exercise 4.1

1. Set your camera to any of the auto or semi-auto modes. Photograph a dark tone (such as a black jacket), a mid-tone (the inside of a cereal packet traditionally makes a useful ‘grey card’) and a light tone (such as a sheet of white paper), making sure that the tone fills the viewfinder frame (it’s not necessary to focus). Add the shots to your learning log with quick sketches of the histograms and your observations.
You might be surprised to see that the histograms for each of the frames – black, grey and white – are the same. If there’s not much tonal variation within the frame you’ll see a narrow spike at the mid-tone; if there is tonal variation (such as detail) you’ll see a more gentle curve. If you find the tone curve isn’t centered on the mid-tone, make sure that you have your exposure compensation set to zero. You may see an unpleasant colour cast if you’re shooting under artificial light, in which case you can repeat the exercise using your monochrome setting (a light meter is sensitive to brightness, not to colour).
This simple exercise exposes the obvious flaw in calibrating the camera’s light meter to the mid-tone. The meter can’t know that a night scene is dark or a snow scene is light so it averages each exposure around the mid-tone and hopes for the best. But why can’t the camera just measure the light as it is? The reason is that a camera measures reflected light – the light reflected from the subject, not incident light – the light falling on the subject. To measure the incident light you’d have to walk over to the subject and hold an incident light meter (a hand-held meter) pointing back towards the camera, which isn’t always practical. If you did that each of the tones would be exposed correctly because the auto or semi-auto modes wouldn’t try to compensate for the specific brightness of the subject.

2. Set your camera to manual mode. Now you can see your light meter! The mid-tone exposure is indicated by the ‘0’ on the meter scale with darker or lighter exposures as – or + on either side. Repeat the exercise in manual mode, this time adjusting either your aperture or shutter to place the dark, mid and light tones at their correct positions on the histogram. The light and dark tones shouldn’t fall off either the left or right side of the graph. Add the shots to your learning log with sketches of their histograms and your observations.

Switching to manual mode disconnects the aperture, shutter and ISO so they’re no longer linked. Because they’re no longer reciprocal, you can make adjustments to any one of them without affecting the others. OCA, Photography 1: Expressing your Vision, p.77-8

Comments

Ex 4.1 setup
Fig Ex4.1A
Setup

[27Dec18]
I ran through this exercise today using a slate table mat, a grey shirt and a sheet of white A4 and photographing the camera's histogram with my iPhone. Realising that the oiled slate might be too reflective, I reran the shots with a dark scarf. I added a cake decoration Santa for seasonal interest in backup shots. Fig 4.1A shows the setup

Ex 4.1.1

Each of the four images Ex4.1B-E is a composite of three photographs: the subject including santa; the associated screen data including the histogram; the subject alone.

Ex41 Ex41 Ex41 /Volumes/SSD01/snaps/BAPhot_Ex_4_1/EX_41_P1050501_paper_auto_santa.jpg
Fig Ex4.1B black slate
Fig Ex4.1C grey shirt
Fig Ex4.1D white paper
Fig Ex4.1E dark scarf

I found this a very interesting exercise. I have often heard this explained in terms of photographing snow and photographing black cats in coal cellars, both of which would be rendered grey through under- and over-exposure respectively. (I think that's right: light turns the negative black which becomes white on the positive but the snow is underexposed, so not enough light gets through to make the negative sufficiently black. And vice versa). But this prosaic use of household objects on the kitchen table really brought the process to life.

All the subjects were rendered grey, especially the second shots without santa diluting the effect.

Ex 4.1.2

Gossen Sixtino
Gossen Sixtino

I first deployed a 1960s Gossen Sixtino light meter (a delight of compactness simplicity and elegance, albeit rather fiddly). It is still working after many years resting in The Cupboard and gave an incident reading of … well I didn't make a note of it but the EXIF data on fig. Ex4.1F shows f/14; 1.3 secs at ISO 1600.

At this point, I had to consult the camera manual as this was the first time I had used it in manual mode. The manual stated that one control wheel alters the aperture, the other, as one might expect, alters the shutter speed but they did not. It took a while on the internet to find a solution. The Micro Four Thirds Talk Forum eventually revealed that,

The 'recording mode' histogram just keeps displaying an interpretation of what the camera is seeing in real-time. Use it in conjunction with Exposure Compensation to shift what the camera is measuring & displaying, to what you wish to record. Then you should see the histogram turn yellow and shift left or right in-relation to the amount of Exposure Compensation you are dialling-in. Hence the semi-auto and full-auto modes go hand-in-hand with exposure comp.
Available in full manual mode only, try turning on 'Constant Preview' (in the custom menu) to reflect your changes of the exposure settings, which can be observed in both the rear screen and the histogram. Deekie, The Micro Four Thirds Talk Forum

Many thanks to Deekie. With that mystery solved, the exercise was completed.

Ex 4.1 Ex 4.1 Ex 4.1
Fig. Ex 4.1F dark scarf
Fig. Ex 4.1G grey shirt
Fig. Ex 4.1H white paper

And it works: black(ish), grey and whit(ish). The exposure compensation indicator continues its quest for grey, showing that the white paper fig Ex4.1H is, in the camera's opinion, 3 stops overexposed. A really enjoyable morning: I learned a lot.

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Ex4.1 Ex4.1
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Page created 27-Dec-2018 | Page updated 30-Jan-2019