Camera Modes (Auto, Program, Av, Tv, Manual)
As it may be some time before we get together again, I have pulled together the following thoughts about camera modes. Please feel free to use this as a starting point for a discussion.
For most photography the Automatic mode on your camera will do a great job and will provide you with an image with a balanced exposure suitable for most conditions. In fact it is possible to always use your camera in automatic mode and get generally good results. The downside of this is that you will never have complete control over your camera, and there will be situations where you will need to take control, for example sporting events or low light situations.
So what do we mean by balanced exposure? This means that the camera will have taken a light meter reading and then made a guess as to the best combination of shutter speed, aperture and ISO to use. This exposure is specific to the current conditions and produces an image that reflects the current level of brightness in front of the lens. Being able to control the settings of the ISO, Aperture and shutter speed ourselves will allow us to control the images that we produce.
Lets have a quick look at each of these variables to see what they do.
This is how long the shutter is open for on your camera.
The faster the shutter speed the more able you will be to freeze the action.
As a general rule do not try to handhold a camera when shooting at < 1/30 of a second unless you want a blurred image.
Try to aim for a minimum shutter speed of 1/focal length of lens.
Minimum shutter speeds that I would use are.
Landscapes > 1/50
Portraits > 1/100
Someone Running > 1/300
Aircraft & Birds in flight > 1/2000
This is the size of the hole in the lens that allows the light in. In general When the aperture is large the image will have a small depth of field. When the aperture is large there will be a small depth of field. A large depth of field is useful when photographing a landscape, and a short depth of field gives a nice blurred effect for a portrait.
As the size of the aperture increases, this is represented as a smaller number, which can be confusing when you first look at these settings.
The F numbers are not a linear relationship.
An F4 lens allows half as much light in as a F2.8 lens.
An F5.6 lens allows in half the light of a F4 lens.
Zoom lenses with a large aperture F2.8 or F4 tend to be very expensive.
Very Blurred Background.
You will note from the image above that the background is very blurred when compared with the previous image. This is because the previous image was taken with a lens with a 35mm focal length, whereas the second image was taken with a 300mm lens. So the amount of background blur is effected by both the aperture of the lens and the focal length of the lens.
This is a measure of the sensitivity of the camera sensor.
The price you pay for increasing the ISO is that the image has an increased level of noise. This is similar to grain on a film camera. Each doubling of the ISO doubles the sensitivity of the sensor, which means that you only need half as much light to achieve the same exposure.
Cutting to the chase.
The following settings will all produce the same balanced exposure. I am assuming that the focal length is not changing.
F4, 1/200, ISO 100
F5.6, 1/200, ISO 200
F2.8, 1/100, ISO 100
F4, 1/400, ISO 800
F5.6 will provide a much larger depth of field than F2.8
F2.8 will have a shallower depth of field.
ISO 800 will have more noise than ISO 100.
1/400th of a second will freeze the action better than 1/100 second.
We have a number of ways to control the exposure.
The following settings are for a Canon camera. I am led to believe that other manufacturers are available.
The key thing to remember is that it does not matter which mode you use to achieve the exposure settings, the exposure settings themselves are what matters. The photo will be the same, if the exposure is the same whether taken in either manual mode or Automatic mode.
In all modes you can either run with either a fixed or an automatically set ISO.
This will provide the same initial settings as automatic mode. It is then possible to switch between a list of equivalent exposures.
Aperture Priority (Av)
This mode allows you to specify the aperture. The shutter speed (and ISO) will vary to create a balanced exposure.
Shutter Priority (Tv)
This mode allows you to specify the shutter speed. The aperture (and ISO) will vary to create a balanced exposure.
Manual Mode (M)
This mode allows you to specify the shutter speed, the aperture (and ISO). The system will use its built in light meter to show if the image is under or over exposed.
If I go out to photograph birds, I may use any one of the following methods to get my pictures. They will all deliver acceptable results.
Set the shutter speed to 1/2000 of a second using shutter priority and I will let the ISO and aperture take care of themselves.
Set my aperture to its largest size (F5.6) and then set my ISO to the largest value I dare (Say 6400) and let the shutter speed run as fast as it can.
Manually set my shutter speed to 1/2000 and my aperture to F5.6 and set the ISO to automatic mode.