DSLR Beginner’s Course

Taking Control of Your Camera

The Basics of Exposure

• What is photography?

• Capturing light.

• Correct exposure is achieved by capturing the correct quantity of light.

What happens when exposure is incorrect?

Underexposed Overexposed

Three Controls of Exposure

• Shutter speed – The duration of time that the shutter opens to allow light into the camera (e.g. 1/60th of a second).

• Aperture – The size of the lens opening through which light can enter. Like the pupils in our eyes, it can open

bigger or smaller to allow or restrict the amount of light. The setting for the aperture is expressed as a ratio (e.g. f/4 or f/8). This is also called the “f-stop”.

• ISO – The sensitivity setting of the digital sensor. Most DSLRs have a “base” ISO of 100 or 200. When a

higher setting is used, the incoming light is amplified electronically to give a brighter image. The advantage of high ISO settings is the ability to achieve the same exposure when there is less light available. The disadvantage is that the resulting image will be grainy or noisy.

Getting to know your camera

Understanding your settings

What do all of these boxes mean?

The Light Meter

• As the name implies, it measures the amount of light in a given scene.

• In-camera meters take reflective readings of a scene.

• A reflective light meter assumes that the world is gray, and therefore, it can easily be fooled.

– Example: In the same environment, a white piece of paper will reflect a lot more light than a black t-shirt.

• A reflective reading must be interpreted to ensure a correct exposure.

The Light Meter, cont. • Metering Modes

– Evaluative/Matrix (default mode) • The camera divides the scene into several zones, and uses its knowledge of common

situations to choose the best exposure. This mode is the most effective in the majority of situations, but can fail in backlit or other challenging lighting conditions.

– Center-weighted average • Similar to evaluative/matrix mode, but gives more weight to the exposure in the

center of the frame than the edges.

– Partial and Spot • These are two separate modes, but are very similar. Partial and spot metering only

reads a portion of the scene, and ignores the rest. This setting is useful for those challenging situations where evaluative/matrix might not do a good job.

The Light Meter, cont.

• Comparison of partial vs. spot metering:

The Light Meter, cont.

• Metering settings in menus:

“Zero” out your exposure

• Set cameras to manual (M) mode. – In manual exposure mode, all the exposure settings (shutter speed, aperture, ISO) are

controlled by you.

– The light meter is still active, but the camera no longer uses it to set the exposure.

• Learn to read the light meter in manual mode. – The scale is usually a range from -2 to +2 or -3 to +3.

– When the meter is in the middle, or at zero, this is the recommended exposure.

– Each number in the scale is a factor of 2, i.e. +1 is twice the exposure as 0, while -2 is half the exposure of -1. This is also called a “stop”, i.e. +1 is one stop more than 0.

– If the meter is blinking at the edge of the scale, it means that the meter reading is off the scale, and the current exposure value is more than 2 stops from the recommended setting.

“Zero” out your exposure, cont.

• Change the exposure settings to “zero” the meter out. – If the meter is on the negative side, zero it by increasing the exposure. Likewise, if the

meter is on the positive side, zero it by decreasing the exposure.

– Using what we know about the three controls of exposure, we can increase exposure by:

1. Slowing down the shutter speed

• Changing the shutter speed from 1/100th to 1/50th will increase the exposure by a stop.

2. Opening up the aperture

• A smaller F-number means a bigger aperture. f/4 is a bigger aperture setting than f/8. Try making your F-numbers as small as possible.

3. Increasing the ISO setting

• Indoor settings are typically much darker than outdoor settings, and very high ISO settings are necessary to get an adequate shutter speed. Try 1600 or 3200 to start.

Shutter speed, in detail

• In most situations, there is a minimum shutter speed required to achieve a sharp image.

– Two rules to remember:

1. When handholding the camera, the shutter speed should be at least “1/focal length”, i.e. for a 50mm lens, the minimum shutter speed is 1/50th, while a 200mm lens needs to be 1/200th or faster.

2. For moving objects, such as moving people, the minimum shutter speed is 1/125th. For faster moving objects, such as athletes or cars, the minimum shutter speed is 1/250th or even higher depending on their speed and direction of movement.

– Both rules should be applied together, and the higher minimum speed should be the one used. Remember that these speeds are only guidelines. If you still see unwanted motion blur, the easiest solution is to increase the shutter speed.

Shutter speed comparison

1/20th 1/2500th

Aperture, in detail • Also called the f-stop, and is expressed as a ratio, where “f” stands for “focal

length”.

– For example, when using a 50mm lens, f/4 means an aperture size of 50mm/4, or 12.5mm.

• The f-number is the denominator in the fraction. Therefore, a smaller f-number means a bigger aperture, and vice versa.

• Lenses have a maximum aperture and a minimum aperture, which is the largest

and smallest that the aperture can be set to, respectively.

Aperture, in detail, cont.

• Lingo: “open up” means to increase the aperture, while “stop down” means to make the aperture smaller.

• The aperture setting will affect both the sharpness and the depth of field of the an image.

– Sharpness: most lenses will produce the sharpest images when set 2 stops down from the maximum aperture. For a lens with a maximum aperture of f/5.6, the lens will be sharpest around f/11. Using a smaller aperture also increases the margin of error for focusing.

– Depth of Field: using a large aperture will result in images with shallow depth of field. This allows selective focus on a certain element, while leaving the rest of the frame out of focus. Conversely, using a small aperture results in images with a deep depth of field, allowing both foreground and background elements to be in focus.

Depth of Field • Defined as the distance between the nearest and farthest points in a scene that

appear acceptably sharp.

• Two factors determine the effective depth of field in an image:

1. The physical size of the aperture.

• A bigger aperture will result in a shallower depth of field. With everything else being equal, an image shot with a 200mm lens at f/4 will have less depth of field than one shot with a 50mm lens at f/4, since the first image used an aperture size of 50mm, while the second used an aperture size of 12.5mm. For this reason, telephoto lenses tend to produce images with shallow depth of field, while wide-angle lenses tend to produce images with deep depth of field.

2. The focus distance.

• Focusing on something inches away will put the background more out of focus than focusing on something a few feet away. This is due to the relative distance between the focus point and the background. A bigger relative distance means less depth of field. Visualize this effect by closing one eye and focus on a finger at different distances.

Depth of Field examples

85mm lens, f/1.4 400mm lens, f/2.8 14mm lens, f/16

ISO sensitivity, in detail

• Since high ISO settings produce unwanted noise, it should be kept as low as possible.

– When shooting outdoors in daylight, stick to ISO 100 or 200, as there is an abundance of light to achieve the minimum shutter speed, or a reasonable depth of focus.

– Change to ISO 400 or 800 for very bright or fairly bright interiors. Remember to pay attention to the shutter speed, and adjust the ISO value according.

– In dim interiors or shooting at night, ISO 1600 or higher is usually necessary to achieve a reasonable shutter speed.

• In low light situations, high ISO settings are unavoidable, and should be used if necessary. While not ideal, a correctly exposed high ISO image will be better than one that is underexposed or blurred.

ISO Noise Comparison

White Balance

• Our eyes are able to quickly adjust to different lighting conditions, and we can perceive a wide range of colors as “white”. While the following conditions produce significantly different color temperatures, we perceive the color of light to be more or less the same:

– A clear day with direct sunlight (5000k).

– An overcast sky (6000-6500k).

– Indoor fluorescent lighting (4000-4200k, with a green cast).

– Household lighting with “soft white” bulbs (2700-3100k).

• Cameras must be given a reference point in order to know what is white. If set to sunlight temperature, images taken in overcast conditions will have a prominent blue cast, while indoor photos will result in orange/yellow skin tones.

White Balance, cont. • By default, the white balance setting is AWB (auto white balance).

• This mode will set the appropriate white balance most of the time, but it can fail in some common situations:

– When the frame is dominated by a single color, AWB will not be able to find a reference to set the correct white balance.

– AWB has a range of 3000-7000k, which means that there are many lighting conditions that fall outside of its range. Most notably, household bulbs are typically 2700k, and AWB is unable to render this correctly.

• When AWB fails, there are two solutions:

1. Take a photograph of something known to be white, such as a piece of paper and set a custom white balance.

2. Shoot RAW and adjust the white balance in post-processing.

White Balance examples

AWB (3450k) Corrected (2500k) AWB (3450k) Corrected (2500k)

Choosing RAW or JPEG

• Advantages of shooting JPEG:

– Convenience: ability to view and share photos immediately without additional software.

– Smaller file size: shoot more images on media card.

• Advantages of shooting RAW:

– Control: retain the ability to set white balance in post-processing, and the flexibility to process the image in multiple ways.

– More image data: allows significantly more room for exposure corrections and noise reduction.