Project 2: The Exposure Triangle – Aperture Priority

Getting things in focus!

(Note #1: A review of what we discussed during activity period is first. Skip this and go to the bottom where the Project is covered if you know this already.)

(Note #2: This whole discussion assumes we are talking about using available light, and not using a flash to change the conditions.)

At the club meeting today, we discussed taking the camera off full automatic mode, and taking creative control of the three elements of proper exposure.

Without repeating everything, let me hit the highlights so you can come back here for a reminder if you find you need a refresher.

The three elements are of proper exposure are:



(image from googleimages)

These three elements work together to produce a properly exposed image. If you change one of them for whatever reason, the other 2 must be balanced so the correct amount of light reaches the camera's sensor.

ISO - This is the measure of the sensitivity of the camera's sensor to light. The higher the number, the more sensitive the sensor is. At ISO 800 or 1600, you can take pictures of stars!

Sample settings are:

100 - outdoors in bright sunlight
200 - outdoors on a cloudy or overcast day, or possibly brightly lit indoors
400 - evening, indoors perhaps where a flash is prohibited - concerts, churches, sporting events, museums
800 - dimly lit, nighttime picture taking
1600 - etc

Higher ISO settings result in grainy pictures which can be an interesting effect if that's what you're aiming for. Refer to the manual for your camera and figure out how to change the ISO setting to match the lighting conditions. Remember to change it back when you are finished!

For more on ISO settings and sample images, check here.


Shutter Speed - The amount of time the shutter is open allowing light to reach the sensor. The shutter is used to stop the action in a moving scene, or to allow blur to give the feeling of motion.

Shutter speeds are measured in seconds; either fractions of a second, or full seconds.

Sample settings are:

1/60 - meaning the shutter is only open for 1/60 of a second.
1/125 - open for 1/125 of a second
1/250 - etc
1/500 - etc

or:

1" The shutter is open for 1 second
2" Open for 2 seconds
4" etc...


Faster shutter speeds allow less light in because the shutter is open for a shorter period of time, and this helps freeze the action.

Think about how you want the final picture to look. Do you want to freeze the action? Then a faster shutter speed is needed. (1/250 or 1/500) If you want blur, a slower shutter speed will work. (1/30 or 1/15)

A quick note on blur: There are 2 kinds of blur that can occur in photos. One is caused by the motion of the subject, or other objects in the frame. The other is caused by the motion of the camera when you don't or can't hold it steady enough.

The difference between the two types of blur is that for the first, only moving objects appear to be blurry. Non-moving objects appear clear and sharp. For the second, when the camera is unsteady, everything appears blurry, even objects that are not moving, and the shot is almost certainly ruined.

The simplest way to control camera shake is to hold the camera correctly. Check here for a quick overview.

Motion blur can be controlled by faster shutter speeds. If you must use a slow shutter speed, a tripod will be necessary to stabilize the camera.

For more on shutter speed and some sample pictures, check here.

Aperture - This is the opening in the lens which can be adjusted to let in more or less light. You chose the size of the opening, and the camera matches that setting with the correct shutter speed. The main purpose of controlling the aperture is to control how much of the frame is in focus, and how much of the foreground and background are out of focus. (The DoF, or "depth of field")

Aperture settings are called f-stops, and are usually whole numbers or written in decimal form.

Sample settings are:

f/22 - the opening is very small limiting the amount of light allowed in; everything will be in focus all the way out to infinity; great for landscapes.
f/16
f/11
f/8. mid-range setting; good for sports
f/5.4
f/2.8
f/1.8 the widest setting allowing the most light in; depending on the distance from the camera, only the subject will be in focus while the foreground and background will be out of focus. Great for portraits.

Here is a video tutorial:



For more on aperture and some sample pictures, check here.


These 3 elements (ISO, aperture setting and shutter speed) need to be balanced to achieve a properly exposed photo. If you get it wrong, the picture will either appear too light or too dark. When this happens, think about what steps you can take to correct it. Do you need more light or less?

If you need more light because the picture is too dark, use a slower shutter speed and let more light in. (1/60 instead of 1/125 for example) But remember, your picture could be blurry because the motion can't be frozen as well at slower shutter speeds, and because it's harder to hold the camera steady.

You could try a wider aperture. (f/2.4 instead of f/8.0 for example) This will let in more light, but will also change the depth of field.

You can also increase the ISO setting to increase the sensitivity of the camera sensor. But remember, the higher the ISO, the more grainy the pictures will appear.

If the picture is overexposed and you need to let in less light, use a faster shutter speed, a higher aperture setting, or lower the ISO.

The best way to learn is to make a conscious decision to try to take a picture a certain way. For example, a portrait of a family member where the background and foreground are out of focus. Then, experiment with your camera settings and take a lot of pictures until you get a feel for it.

Here's a good step-by-step procedure.

1. Set your ISO to match the lighting conditions. (see the section on ISO above. Check your manual for how to change your ISO setting.)

2. Set your camera on Aperture Priority mode. (Av on the dial - or check your manual for how to do this.)



(this is my camera)

3. Set your aperture to a low setting - f/2.8 or lower if possible. Check your manual for how to change the aperture to a low setting once you take the camera off full automatic mode. (The green rectangle is full automatic mode in the picture above. Turn the dial back to full automatic mode when you are done with your photo session.)

4. Set up your shot. If you are doing a portrait of a person, make sure there is a foreground and a background that will appear out of focus. If you are shooting still life objects, put them far enough apart in the foreground and background that some will appear out of focus.

5. Focus on your subject. No need to worry about the Rule of Thirds for this project, but if you want to use it, you may want to set your camera on manual focus. Remember that most cameras focus on whatever is in the center of the frame. Use "Focus Lock" to focus on subjects that are not in the center, or put the camera on manual focus. (See my earlier article on focus lock here.)

5. Experiment! Take several shots of the same setup with different objects in focus. (See my chess photo below. How could I redo this setup differently? Want to try it yourself?)

6. Post a couple of your shots here for all of us to see! Send me an email and I will make you an Author: dmohr@edenca.org

7. Have fun with it!!


Project 2: Aperture Priority and Depth of Field.

This week's project assignment is to learn how to take photographs where the subject is in focus, but the foreground and background are out of focus. You should take some portrait shots of people, and some still life shots of objects around your house or the school. (Try both!)

Take some close up shots of objects sitting on a table at different distances from the camera.

Here are a couple sample shots I took to demonstrate the technique.



The knight on the right is in clear focus while the rook in the foreground and the queen in the background are out of focus. (Click the picture for a closer view.) Also notice this picture is a bit grainy because I used ISO 400. This is called "noise".



Most of the wasp is in focus, but the leaves in the foreground, and the foliage in the background are out of focus. If you look closely you can see that the DoF is so narrow that the entire wasp isn't in focus. The legs closer to the camera are a bit blurry. A higher f-stop will correct this.



I couldn't tell at the time by looking at the picture on the camera's preview window, but when I loaded it onto my computer and looked at it full size, I noticed that the trees in the foreground were in focus, but my family behind the trees were out of focus because the DoF was too narrow. The camera auto-focus assumed I wanted the trees in focus.

This could be corrected by either putting the camera in manual focus mode, or using a higher f stop.