One: Equivalent Exposure
Here are the main topics we covered during our first few lectures. You should know how to control and manipulate each of the fundamental components below. Note that some topics may go into more detail than what we have covered so far as a class (i.e. the aperture-sharpness bell curve or types of noise) – don’t worry, we’ll look at such topics in class later.
- ISO
- Shutter Speed
- Aperture
- Depth of Field
- Equivalent Exposure
ISO:
ISO refers to the sensitivity of the sensor itself. The higher the ISO, the less light is needed to take a properly exposed photo. However, higher ISO speeds yield larger amounts of noise (akin to film grain) compared to lower ISO speeds. Generally, having less noise is preferred, so unless you need to use a faster shutter speed, it’s typically better to use the lowest ISO possible while still maintaining a shutter speed equal to or greater than your focal length.
Shutter Speed:
Shutter speed refers to the length of time that the camera shutter remains open. The longer the shutter is open, the more light hits the sensor. In order to produce a reasonably sharp image, the shutter speed should roughly equal or exceed the camera’s focal length. Thus, if you’re shooting with a telephoto lens at 200mm, your shutter speed should also be at 1/200 or faster. Note that some lenses/cameras feature stabilization technologies that can allow the photographer to use a slower shutter speed than would otherwise be feasible.
Note: If you need a slower shutter speed on-the-spot, the average person can hold a camera relatively still at about a 1/30-1/50 shutter speed; however, if you are able to brace the camera on a solid object or have access to a tripod, this would help tremendously!
Aperture:
Aperture refers to the size of the opening in the lens that allows light to pass through to the sensor. The smaller the f-stop number, the larger the aperture opening (it’s counter-intuitive). Thus, f/2 is larger than f/8. If the aperture is larger, then less light is necessary to produce an equivalent exposure. Apertures come in whole stops that can be further broken down into half or third stops. They are:
f/1.0 Larger
f/1.4
f/2.0
f/2.8
f/4.0
f/5.6
f/8.0
f/11
f/16
f/22
f/32
f/45
f/64
f/90 Smaller
Generally speaking, you will find that the resolving power of a lens increases as you stop the lens down (increase the f-stop number) up to a certain point, usually f/8.0 to f/11. At that point, the resolving power of the lens will begin to decrease, creating a bell-curve. This phenomena is independent of depth-of-field. While it is true that increasing the f-stop number will result in a larger area of the image being rendered with acceptable sharpness, the resolving power of the lens is at its greatest somewhere in the middle of its aperture range.
For example, a photograph of a forested mountain taken at f/22 will be softer than the same scene taken at f/8.0. Although the DOF is greater with the f/22, the overall image is less sharp. Note that most people probably will not be able to tell the difference in sharpness, and those that can will probably be pixel peeping. At any rate, the point of this explanation is that unless you truly need to maximize your DOF (for example, with landscapes or 1:1 macro work), you’re better off shooting with mid-level apertures, IF the goal of your photography is to maximize sharpness. Don’t use f/8.0 if you want to induce bokeh.
Depth of Field:
Another consideration when selecting your aperture is its relationship with depth-of-field. Depth-of-field, or DOF, refers to the portion of the image that is in focus (rendered with acceptable sharpness). Larger apertures have a smaller DOF, and smaller apertures have a wider DOF. This means that at larger apertures, less of the photo will be in focus, whereas with smaller apertures, more of the photo will be in focus. For instance, if you were taking a picture of a box, with a large aperture, you could only get maybe one edge or face of the box in focus, and with a smaller aperture, you would be able to get the box as well as the background in focus. Remember that: larger aperture opening = smaller f/stop #, smaller aperture opening = larger f/stop #.
Equivalent Exposure:
Equivalent exposure simply refers to getting the same amount of light in an image through different means. For example, if you were taking a picture of the campanile at dusk, there wouldn’t be very much ambient lighting. Thus, your camera might tell you to take the photo using these settings: f/2.0 – 1/15 – ISO 1600. But what if you wanted to maximize sharpness and DOF and minimize chroma noise? Assuming you had a tripod, you could shoot this scene using these equivalent settings: f/8.0 – 4 seconds – ISO 400. Granted, the image may gain some noise from the long exposure, but the latter settings would probably yield a better photo, while still exposing the scene correctly and equivalently.
