Learning Light: Exposure

For every photographer, there are two pillars on which his credibility as a successful photographer and artist rests on, namely mastery over exposure and composition. As composition is an artistic skill, which is to be nurtured and develops over a long period, exposure is that technical skill a photographer can study, practise and master within a short period. This also points out the beautiful combination of subjective and objective, art meets science nature of photography which attracts so many enthusiast from various cultural and academic backgrounds. Today we shall unravel the mysteries of the big E, the foundation of any successful photograph- Exposure, and why we need to master it, in order to be a skilled light magician. 

Exposure

Exposure value(EV) numbers are a way to describe exposure settings with just a single number, instead of the usual f-stop and shutter speed combination. A single number represents all combinations of apertures and shutter speeds that give the same exposure. Just for a preliminary understanding, have a look at the following table.

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For example, EV10 in the table can represent any combination of aperture and shutter speed from 4 sec at f/64 to 1/1000 sec at f/1.

Light Meters 

Light meters are designed either to measure light reflected from the subject (the meter in your camera) or to measure light falling on the subject (a hand-held incident light meter). 

Modern cameras use reflected light meters that work through the lens (TTL). They usually have adjustable sensitivity patterns. Centre Weighting is common as this takes more account of the subject in the centre of the frame. So-called Spot metering in camera is better thought of as small-area metering; a true spot meter measures are much narrower angle between 1 degree to 5 degree, which makes many cameras spots look crude indeed.

Evaluative metering is now found in many forms, with all major manufacturers having their own brand names. Essentially, a scene is broken down into metering areas, sometimes over 1000. The brightness distribution that is measured is compared against a database of image measurements and compensation made accordingly. The modern cameras also take into account the focal length of the lens. 

Handheld incident light meters usually have a diffuser (sometimes called a lumisphere) over the light-sensitive cell to average the light falling on the subject. On some models, this can be moved aside and the meter used as an averaging reflected light meter by pointing it at the subject. Spot meters are simply reflected light meters that measure from a much smaller part of the subject. Camera spot meters are not as selective unless a telephoto lens is used TTL (through the lens) reflected light meter in cameras that measures light through the lens.

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2b (2)

 

Exposure Compensation 

Reflected light meters are easily fooled as they expect to see an average scene. The reflectance of the average scene equates to 18% grey. Light meters try to interpret what they ‘see’ in terms of the average scene. A predominantly light subject will give too short a suggested exposure, often underexposed by 2 stops. Similarly, an all-dark subject will result in overexposure by up to 2 stops. Exposure compensation or manual override will be needed when the subjective is not average- black dogs or white flowers filling the frame, for example. 

Techniques for the perfect exposure 

There are several ways of getting accurate meter readings. Never forget the meters always read for middle grey (18% reflectance). 

-Take a general reading

 Often a reading from an entire subjective gives a good exposure. If the subject is predominantly light coloured or white then add light. Conversely, for predominantly dark subjects cut down on the reading suggested by the meter. For the proverbial black cat, you will need to reduce the exposure by upto 2 stops.

3a

-Using a Grey card 

An 18% reflectance grey card gives the meter what it wants to see. Hold the card in front of the subject and meter off that. Set the camera ignoring what that meter now tells you (you must be in manual mode). Also, if you do not have a grey card, use your hand held in front of the subject. Don’t let the shadows fall from your fingers and holder hand out flat. Brown skin almost matches a grey card perfectly.

4a (2)

-Measure the light falling on the subject 

Using a hand-held incident light meter can be beneficial as they supply an averaged reading of the light falling of the subject and do not read dark and light areas of the subject. This can be a good idea in extreme lighting conditions. Remember to point the meter back towards the camera position.

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-Averaging the readings from the shadows and highlight 

As meters read middle grey, the correct reading will be somewhere between the reading for the darkest and lightest areas of the subject. If the reading is 1/250 at f/5.6 at the lightest part and 1/15 at f/5.6, shoot at 1/60 at f/5.6, which is in between the two. 

-Bracketing 

One way to get the right exposure is by playing it safe and taking additional under and overexposed images. This may not be possible with some fast-changing subjects. Take any type of meter reading then shoot additional frames whole or half stops under- and overexposed in a series of three or five frames. Needless to say, this cannot work with candid photography where you can get one shot only. It is best for still-life though.

-Meter the shadows and compensate

Metering shadows and compensating for them will guarantee that you get shadow detail. Take a meter reading from the darkest read where you want detail. Then expose at 2 stops less. If the meter says 1/60 at f/2.8 use 2 stops less- 1/60 at f/5.6.

High Dynamic Range (HDR) imagery

The average outdoor scene has a range of 7 stops, but many photographers work with the exception and not the average. Their high-contrast scenes will show a range of 10 or even 16 stops. The mass of digital images are commonly stored as 8-bit files that give a range of 8 stops, which is 256:1. Our eyes are capable of an instantaneous 1000:1.

When capturing images in RAW, most cameras use 12-bit processing and can capture a range of 12 stops of 4096:1. Thus, by capturing a much wider dynamic range, an ’instance’ must be created on the computer that corresponds to just one exposure from the range of possibilities. Thus, the idea is to combine multiple exposures which capture the range from highlights to shadows.

Adobe successfully introduced photographers to HDR with the ability to extending imagery to 32-bit when Photoshop CS2 was launched. This software feature allows users to merge a number of different exposures into a single file to more accurately represent the human perception of the scene.

Although two images are sufficient to create an HDR, it is always better to have a series of multiple exposures taken at regular intervals say +2EV, +1EV, Normal exposure, -1EV and -2EV works best.  These exposures are merged into a single file that has an extended dynamic range with detail in both shadows and highlights.

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Thus, HDR merge gives the photographer control both over contrast of the final image and of the ways in which highlights are handled. Although with HDR we can retain full detail in Highlights and Shadows – the technique can have a specific ‘look’, rather like a super-realist painting. This could become stale if overused.

Conclusion

The above guide and information shall help you all fellow photographers. As far exposure goes, it’s a very essential element in every photograph which decides the final look of your photograph. Next up our series, we shall have a look at different light sources we a photographer can create photographs in. Until next time, ciao!

 

                -Chanakya Wable

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