This lesson can be downloaded here: http://www.yousendit.com/transfer.ph...DF343D5520BD1E

Aperture

Aperture is the opening in the lens(diaphragm) that allows light to enter the camera to record on its medium (either the digital sensor or film itself… does anyone use film?? What is film???) Be sure you understand how to adjust the aperture on your camera.

Aperture is designated by f-stops. The f-stop is actually the ratio of the lens opening (in millimeters) in relation to the focal length of the lens. If you want to give yourself a headache, read up on the numbers in your Understanding Exposure book (it’s spelled out in the previous chapter, “The Exposure Triangle”). In this lesson, we are going to pay attention to how changing the aperture works and how it affects the image.

When you think about f-stops, think about everything being OPPOSITE. Smaller f-stop values represent a wider, or rather LARGER diaphragm opening. Larger f-stop values represent narrower or SMALLER openings. Think of the aperture as the pupil in your eye. Your pupil can open up to let in more light, or it can constrict to reduce the flow of light into your eye. The aperture on your lens can behave the same way. You can choose a low f-stop (wide aperture) in low light situations, or a large f-stop (narrow aperture) when there is plenty of available light.

There is more to changing the aperture than just allowing less or more light to enter the camera. Changing the aperture also affects the depth of field(DOF). The DOF refers to the planar area (front to back) of the image that is IN FOCUS. Lower f-stops will yield a shallow DOF, giving you that smooth blurred out background. Higher f-stops will yield a deeper/larger DOF. Changing your aperture can be a useful tool in creative composition of your images.

Here is a diagram, visually explaining depth of field:


Exercise 1 – follow this link: http://www.dofmaster.com/dofjs.html
**The camera brand/model does not matter in this exercise

• Set your focal length to 50mm. Then set your subject focus distance to 10 feet. Note the TOTAL depth of field in the right hand column. Try again with the same lens focal length, but change your focus distance to 5 feet. What do you notice happening to the depth of field as you move in closer to your subject (reducing the focus distance)?
• Set your focal length to 50mm. Then set your subject focus distance to 5 feet. Note the total depth of field in the right hand column. Try again with the same focus distance but change your lens focal length to 85mm. What do you notice happening to your total depth of field as the lens focal length changes yet the subject’s focus distance remains the same?
• What can you infer about the relationship between aperture, lens focal length, and the subject’s focus distance?

Storytelling apertures – This is usually used in a broad sweeping landscape, where you want your image to be in focus, all the way from front to back, using a SMALL aperture/large f-stop.
Singular theme apertures – This is used for selective focusing, where you want to blur out a background, or make one object pop out of the picture and leave the rest of the image blurry. Here you will use a LARGE aperture/small f-stop.
Who cares? apertures – This is used when you need optimum sharpness but your composition doesn’t call for crisp sharp focus from front to back, or if your subject doesn’t need to be separated from the foreground or background. These f-stops are usually f/8-f/11, and are many times used in studio situations or if the subject is up against a flat wall.

Why use a “who cares?” aperture? The size of the diaphragm opening at f/8-f/11 is equivalent to the centralized “sweet spot” or optical center of the lens. The light coming through the lens at the optical center is not dispersed, but passes straight through the lens. Smaller apertures, like f/22 will allow light to only pass through the very center of this sweet spot, yielding the image in focus from front to back. Larger aperture, such as f/5.6 and lower allow light to enter outside this centralized “sweet spot.” The light rays that enter the lens outside of the optical center are dispersed, and are dispersed more as the light nears the extreme edge of the lens. This light dispersion is what gives a shallow DOF (those smooth blurry backgrounds/foregrounds).

Exercise 2 – This will seem like a repeat of the last lesson’s exercise, but you will be noting a different effect this time.

• Set your camera to APERTURE PRIORITY MODE.
• Choose a stationary object for a subject (e.g. flowers, doll, bear, lawn ornament) in a well lit area, and have it nicely separated from it’s background.
• Set your aperture to the lowest f-stop available (this will vary depending on your camera and your lens). Fill the frame with your subject, but leave some of the background visible in your frame. Take your picture.
• Now set your aperture to a larger f-stop. Repeat the previous step.
• Repeat these steps, each time using an even larger f-stop than the previous image. Take note of how your background changes in each picture.

Exercise 3 – Share three pictures, one with a storytelling aperture, one with a singular theme aperture, and one with a who cares? aperture. Tell us what aperture you used, and why you used it in that particular image.



I know this information might be a bit confusing at first, so if you have ANY questions please be sure to post them here, and I will do my best to get them answered in a timely manner.



Siggies off please!