To begin shooting in Manual Mode, you'll first need to understand how three variables affect the outcome of your image:
1. ISO (film sensitivity to light)
2. Shutter Speed
ISO, simply put, is your film's sensitivity to light (aka, film speed). ISO is measured in steps with numerical values starting from 100 increasing to 200, 400, 800, 1600, etc. Each step doubles the sensitivity of your sensor. The lower the number, the less sensitive your sensor is to light; and as the value increases the more sensitive it becomes. Your lowest ISO value, or base ISO, is the highest quality image your camera can produce without adding noise (graininess) to your image. Ideally, you would try to shoot at the lowest ISO possible, however it's not always possible to do that --especially in low light situations.
So what does that mean, exactly?
Well, since sensitivity doubles with each increasing "step" an ISO of 200 is twice more sensitive than 100, 400 is twice more sensitive than 200, etc. This makes an ISO of 800 eight times more sensitive than 100; meaning it needs eight times less time to capture an image.
So...if your camera sensor needed one second to capture a subject at an ISO of 100, if you shot the same subject at 800, you'd only need 1/8th of a second.
Remember, that if you are increasing the ISO, the trade off is that you will be adding noise or graininess to your image!
Shutter Speed is the amount of time your camera's sensor is exposed to light by the opening and closing of the shutter. It not only controls the exposure speed, but also controls how your camera freezes motion. Shutter speed is measured in fractions of a second, with fast exposures like 1/4000 and very slow exposures like 1 second or longer. The longer the shutter is open, the more light the sensor is exposed to. Therefore, the longer the shutter is open the lighter the image. However, the slower the shutter speed the more it will blur an object in motion.
Inversely, a fast shutter speed allows less time for the sensor to be exposed to light, so the image is darker but it will freeze moving objects faster.
Aperture is the most difficult concept of the three variables to understand. Aperture controls how wide your lens opens. The wider the opening, the more light can be let in as the shutter opens and closes, therefore the lighter the image. The narrower the opening, less light is let in and the darker the image. As the aperture is opened and closed, it also affects the angle at which light strikes your film --which affects your depth of field.
Depth of field, simply put is how sharp or blurry objects in the background are in relation to your subject. A large depth of field means that objects far away from your subject in the background are sharp. A shallow depth of field means that objects in the background are blurry.
Aperture is measured in f/stops (which is a ratio size of lens opening to focal length).
A simple way to remember the relationship is:
- Large F-Stop = smaller lens opening = More Light Needed = larger depth of field (sharper background)
- Small F-Stop= wider lens opening = Less Light Needed = shallow depth of field (blurrier background)
So now that we know what these variables are, how do you choose the setting?
1. Consider your lighting situation. Are you in a dim environment or some where brightly lit?
2. Consider how fast your subject is moving. Is it stationary? Is it fast moving?
3. Consider how sharp you want your background to be in relation to your subject.
4. How much will noise is "too much?" You might want to consider print size here too, since the larger the print, the more visible the grain will be.
Asking yourself these questions will help you decide where to make adjustments to compensate for your lighting situation.