The Fundamentals of Exposure

Final Words

In this article we looked at the concept of exposure and illustrated why it is essential that the photographer be in charge of the three exposure parameters:

• Aperture
• Shutter Speed
• Sensitivity (ISO)

This is not to say that fully automatic modes including scene modes have no place in photography. It depends on the circumstances and the extent to which the photographer wants to determine how the photographs are rendered. In a hectic, fast-paced situation a program mode or scene mode could mean the difference between getting the shot and not getting it.

To summarize the effect of the three exposure parameters:

Aperture

• Controls the depth of field and degree of blur of the background. Can be used to make the subject stand out from the background
• A large aperture enables handheld photography in low light
• Affects sharpness and resolution: the widest aperture is generally not as sharp as when stopped down.  Very narrow apertures such as F13, F16, or F22 also reduce sharpness due to a phenomenon known as diffraction.

Shutter Speed

• The key to low light photography. The shutter speed is the exposure parameter that covers the largest range of exposure values. In B mode we can even go longer than the 30 seconds our camera's built-in timer can provide
• Freeze action or deliberately blur action to a specific degree
• At night, make sure your shutter speed is fast enough to prevent motion blur

Sensitivity (ISO)

• Facilitates that we can set a large range of shutter speed and aperture combinations and still achieve correct exposure by adjusting the ISO
• Enables hand held low-light photography
• High ISO values take a toll on image quality

Revisiting Select Examples

A large aperture (small number) like F1.8 blurs the background and makes the subject stand out.

Panning plus a moderately slow shutter speed such as 1/60s leaves the background blurred and the wheels spinning for a sense of movement.  Even slower shutter speeds can be used to show running water, etc.

A fast shutter speed like 1/1000s freezes virtuallty all objects in the frame.

A high ISO like 3200 makes hand-held shooting possible at night.

The Bottom Line

Taking control of the exposure away from the camera's automation opens up a plethora of creative opportunities and is something that everyone can master with a bit of training. One doesn't have to forgo automation all together. The semi-automatic modes like Av, Tv, and TAv let the photographer be in control while still allowing the camera to correctly set the exposure. In M mode the photographer has total control, but it is also the slowest way to work and may therefore not be the best choice for fast-paced assignments.

Being a great photographer doesn't end with understanding exposure, however.  There are certain scenes that cannot be photographed properly without specialized techniques or filters, and many creative techniques that can turn an ordinary image into a work of art.  Therefore, the PentaxForums resource library includes a number of more advanced articles if for you when you've mastered the basics of exposure:

• Exposure Bracketing 101
• Landscape Photography: How to Expose for Mixed Lighting
• Using the Histogram to Get Better Photos
• A Basic Guide to Long Exposures
• Daylight Long Exposures Using an ND Filter
• Long Exposure Composite Photography
• T-Stops vs F-Stops in a Camera Lens
• Metering with M, K and M42 manual lenses

If there is a topic that you would like to see covered in a future guide, please let us know in the comments below.