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Exposure “Exposure” refers to the amount of lighting passing through the lens of the camera and being recorded by the digital sensor or film. Modern cameras have built-in light meters which determine exposure automatically and they do so very well much of the time.
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Exposure “Exposure” refers to the amount of lighting passing through the lens of the camera and being recorded by the digital sensor or film. Modern cameras have built-in light meters which determine exposure automatically and they do so very well much of the time. However, there are times when the meter is fooled and doesn’t get the exposure right. Then the photographer has the power to tweak the exposure.
Basic Exposure Adjustments using the Histogram and Exposure Compensation features of the camera…
The Histogram The Histogram is a bar graph of the tonal values in a photograph. It can usually be displayed on the rear LCD of your camera. It is useful because it helps you adjust the exposure settings of your camera to correct overexposure and underexposure. It helps confirm that you are not “clipping highlights” or “blocking up the shadows”
The Bars and Zones of the Histogram Reflect the maximum range of tones the camera can record “Shadows” -----------“Midtones”---------- “Highlights”
The Histogram Display for a Commonly Photographed Scene that is properly exposed…
Histogram for an Over-Exposed Scene that Suggests the Need for Corrective Action by the Photographer
Histogram for an Under-Exposed Scene that Suggests the Need for Corrective Action by the Photographer
Exposure Compensation (aka “EV Compensation”) is a feature on your camera that allows you to make adjustments to exposure in light of the histogram. Exposure Compensation adjustments are made either through a dial on your camera’s body (often marked with the “-/+” icon) or through a menu (point and shoot cameras)
Exposure Compensation lets you tweak the camera’s automatic meter reading to subtract light (-) or add light (+) as required by the histogram… Exposure Compensation adds or subtracts light in small increments of 1/3 or ½ “stops” or units of light. Use trial and error to determine how much compensation will yield a correctly exposed photo with a good histogram.
Correcting an Underexposed Photo Using Exposure Compensation… Photo taken using the automatic meter reading of the camera (Underexposed)
Correcting an Underexposed Photo Using Exposure Compensation… The effect of adding +2/3 of a stop of Exposure Compensation
Correcting an Underexposed Photo Using Exposure Compensation… The effect of adding +1.3 stop of Exposure Compensation – i.e., too much compensation added; Now it is overexposed.
Summary: • Develop the habit of reviewing your photos immediately after taking them to examine the quality of the exposure • Use the Histogram to assess the exposure – look for an even spread of tonal values across the histogram. Note problem signs: the graph spills over either edge of the graph. • Find and Use the Exposure Compensation dial or menu to add light (e.g., + .3, + .6, +1) to underexposed pictures or to remove light from overexposed pictures (e.g., -.3, -.6, • -1). Recheck the histogram until you eliminate “spilling over the edges.”
Advanced Exposure Control through the manipulation of three interrelated variables allows you to go beyond “tweaking” the auto settings of your camera. It allows you to take more complete creative control of the picture making process: Aperture – the hole inside the lens through which light passes Shutter Speed – the length of time the shutter is open to let light fall on the sensor where it is recorded. ISO (Sensor Sensitivity) – the degree of sensitivity assigned to the sensor.
A helpful analogy for understanding the relationship between Aperture, shutter speed, and ISO sensor sensitivity…. • If you’re thirsty and go to the sink to fill a glass of water to drink, there are three interrelated variables involved: • How much you open the pipe valve with the faucet handle (aperture) • How long you let the water run to fill the glass (shutter speed) • How large of glass you choose to fill (ISO sensitivity)
There are many ways to fill a glass with water… *Open the pipe valve to full *16 oz. glass fills in 5 seconds *Open the pipe valve to ½ way *16 oz. glass fills in 10 seconds Open the pipe valve to ¼ of the way *16 oz. glass fills in 20 seconds
Aperture: The size of the aperture opening in the lens is adjustable much like faucet valve is adjustable. If the aperture is opened to its maximum size, light floods through. If the aperture is opened to its minimum size, light trickles through. Aperture size is measured in F-stops or “Stops”: F/1.0 F/1.4 F/2.0 F/2.8, F/4, F/5.6, F/8 F/11, F/16, F/22, F/32 ---------Larger Apertures---------------- ----------Smaller Apertures---- Each F-stop allows is twice as much light as the one to its right and half as much light as the one to its left.
Several ways to get the same exposure by varying aperture size and shutter speed…. Let’s say your camera meters the scene and suggests the following exposure settings of Aperture: F/8 Shutter Speed: 1/125 second You can achieve the same exposure with different values… F/2.8 F/4 F/5.6 F/8 F/11 1/1000s 1/500s 1/250s 1/125s 1/60s
Shutter Speed Shutter speed is also measured in “Stops” or increments that double or halve the amount of light passing through. Common Shutter Speed Stops… 1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, 1/250s, 1/500s, 1/1000s, 1/2000s, 1/4000s
My head hurts! Why does all this matter? If you can achieve the same exposure with different values… F/2.8 F/4 F/5.6 F/8 F/11 1/1000s 1/500s 1/250s 1/125s 1/60s What does it matter which option I choose? Answer: While each option lets in the same amount of light, Each option also changes other qualities of the picture: Aperture: Determines “Depth of Field”/amount of the picture that is in-focus Shutter Speed: Whether you will get a blurry shot due to motion
Aperture Settings and Depth of Field Depth of Field refers to the portion of the picture that is in focus. A “shallow depth” of field indicates that only a narrow zone of the photo is in focus; “deep” depth of field indicates that a wider zone of the photo is in focus. Larger Apertures (i.e., F/1.4, F/2, F2.8, F/4) create shallower depth of field Smaller Apertures (ie., F/11, F/16, F/22) create deeper depth of field.
Shallow Depth of Field Created with Large Aperture (F/2.8) Exposure: F/2.8, 1/125s
Greater Depth of field Created by a Smaller Aperture (F/8.0) Exposure: F/8, 1/15s
Widest Depth of Field Created by an Even Smaller Aperture (F/16) Exposure: F/16, 1/4s
Portraits often benefit from using A moderately large aperture to achieve narrow depth of field Portraits made at F/2.8 or F/4
Landscape photographs usually benefit from very deep depth of field achieved by using small apertures (i.e., large F-numbers such as F/11, F/16, F/22. The “cost” for small apertures” is slow shutter speeds that often require a tripod. F/16, 1/30s
Effect of Shutter Speed Choices… Slow shutter speeds: blur or capture motion; or allow use of a small aperture and usually require a tripod. F/16 1/2s
So, how do I actually take advantage of all this with my camera? First, look through your viewfinder and locate the current aperture and shutter speed settings. Get used to looking at them whenever you’re making a photo. Second, take the camera out of auto mode and start using modes that let you control settings. “Aperture Priority Mode” (Av) and “Shutter Priority Mode” (Tv) are two places to start. Third, once comfortable with Av and Tv modes, experiment with full Manual mode (M).
Introducing a third variable (ISO Sensitivity)… *Open the pipe valve to full *32 oz. glass *Glass fills in 10 seconds *Open the pipe valve full *16 oz. glass *Glass fills in 5 seconds Open the pipe valve full *8 oz. glass *Glass fills in 2.5 seconds
ISO Sensitivity governs how sensitive your camera’s sensor is to light. The sensitivity of your camera’s sensor is measured by an ISO numbers and each ISO number represents a “stop” of light. E.g., ISO 100 ISO 200 ISO 400 ISO 800 ISO 1600 Each ISO number is twice as sensitive as the number on its left and half as sensitive as the number on its right.
Factoring all three variables in exposure…. Your camera might suggest an exposure such as: F/8, 1/125s, ISO 100 But you want a faster shutter speed to freeze motion… F/8, 1/250s, ISO 200 Or maybe that’s not fast enough because the object is moving very fast…. F/8, 1/1000s, ISO800 What’s the downside of higher ISO? NOISE/Graininess!
Stop, my head’s hurting. If we already have two variables (aperture and shutter speed), why do we need a third variable? Let’s look at a case study, to see the value of having control over ISO Sensitivity as a third variable….
Aperture: F/4.0 (largest on the lens I was using) Shutter speed: 1 second (far to slow for handholding camera) Sensor Sensitivity: ISO 100 (least sensitive setting for my camera’s sensor)
Solution: Change the ISO setting to make the sensor more sensitive to light. This allows a faster shutter speed that I could still handhold. I increased shutter sensitivity from ISO 100 to ISO 1600 (i.e, 4-stops) Aperture: F/4.0 (largest on the lens I was using) Shutter speed: 1/15 second (just fast enough to handhold camera if I braced it against the wall to help reduce camera movement) Sensor Sensitivity: ISO 1600 (second highest sensitivity setting for my camera’s sensor)
If changing each variable has a “cost” what is the cost for Using a high ISO setting such as ISO 1600? Answer: Noise/Graininess in the image that becomes especially visible in large prints.
