Learn the Elements of Exposure

Today’s Photo Tip: Learn the Elements of Exposure. For my first post of the year I thought I would start off with a few photography tips on exposure.  Probably the most import element needed for capturing good quality photos is adequate light. In photographic terms this is referred to as exposure. The two most important physical components that can provide you with an up front advantage in this arena is a ‘fast’ lens and large image sensor.


THE LENS: A lens’ speed basically refers to the maximum amount of light that it can transmit in a specific length of time.  Essentially, a lens that transmits a lot of light is called a “fast” lens. The speed of a lens is determined by maximum size of the lens opening known as aperture. The aperture controls the amount of light that reaches a digital camera sensor. The diameter of an aperture is measured in f-stops. A lower f-stop number opens the aperture to admit more light onto the sensor. Higher f-stop numbers close the lens opening so less light gets through. A lens with an f-number of f/2.8 has a larger aperture than one with an f-number of f/11. The aperture, or aperture range, is indicated on the front of a lens.
 
IMAGE SENSOR: An image sensor is a solid-state silicon chip containing millions of photosensitive diodes called photosites (or sensels) that record light (photons), that converts an optical image into an electronic signal that displays color, tone, highlight, and shadow. Today, most digital still cameras use either a CCD image sensor or a CMOS sensor. Neither technology has a clear advantage in image quality. CCD is a more mature technology and is in most respects the equal of CMOS which are less expensive to manufacture than CCD sensors. Both types of sensor accomplish the same task of capturing light and converting it into electrical signals. Sensor size is analogous to choosing between 35 mm, medium format and large format film cameras. Most digital sensor specifications are expressed in either their size by inches or as a crop factor based upon a full-frame 35mm sensor. Beyond this point everything can get quite techinical and complicated. Suffice it to say, generally the larger the size, the better.


With all that said, what are the manual settings can you employ when taking a picture that will help you get the best exposure possible? Bryan Peterson illustrates the three main ingredients in the following diagram. Each of the three aspects of the triangle relate to light and how it enters and interacts with the camera. ISO is the measure of a digital camera sensor’s sensitivity to light. Aperture is the size of the opening of the lens at the time a picture is taken. Shutter Speed is the amount of time that the shutter remains open during the shot. The intersection of these three elements becomes the image's exposure. From here there is no easy answer.

Mastering exposure is a juggling act that takes a lot of practice. Not only does changing each element impact the exposure, each one also has an impact upon other aspects of the final image, i.e. changing aperture changes depth of field, changing ISO changes the graininess of a shot and changing shutter speed impacts motion blur. Remember, taking digital pictures is free. To learn the various effects that each of these aspects has on a shot, practice by shooting in intelligent Auto mode, Manual mode, Shutter priority mode and Aperture priority mode. The last two semi-automatic modes allow you to make decisions about one or two elements of the triangle and lets the camera handle the other elements. Practice is the best teacher.