When using a camera there are 3 settings that you have to work with: shutter speed, ISO, and aperture. There are many web articles on this topic, but most seem rather long and confusing, so I hope to provide the very basics here.
1. shutter speed/exposure time (Tv): The effective length of time a camera's shutter is open. This can range from very fast 1/2000s to several hours.
Examples: When not using a tripod (handholding) the shutter speed should be at least 1/60 of a second to avoid the photo becoming blurry. I personally try to shoot at 1/200 of a second when handholding if possible. Most of my images are shot using a tripod which allows for longer exposures.
2. aperture (AV): The aperture controls the amount of light that enters the camera. You can think about it like how our eyes get bigger and smaller depending on the amount of light. The aperture setting is displayed as f/#. Most lenses start at f/4 and go up to f/22. f/4 represents a large opening and therefore a lot of light entering the camera. This results in a faster shutter speed and a small depth of field (DOF). f/22 represents a small opening and therefore less light entering the camera. This results in a slower shutter speed and a large depth of field (DOF). Other settings include f/5.6, f/8, f/11, and f/16.
Aperture is probably the most confusing element, but it is important to take the time to understand it so that you can capture the images the way that you want.
How aperture effects shutter speed: lets say that an aperture of f/4 results in a shutter speed of 1/800 of a second. If you change the aperture to f/5.6 the shutter speed then becomes 1/400 of a second. Change the aperture to f/8 the shutter speed becomes 1/200 sec. Aperture f/11 to 1/100 sec. f/16 to 1/50 sec. f/22 to 1/25 sec. Basically as you increase the aperture by 1 stop the amount of light entering the camera decreases by 1/2 resulting an a shutter speed being reduced by 1/2. The confusing part is that increasing the aperture number (going from f/4 to f/5.6) actually means that you are decreasing the opening and causing less light to come into the camera.
depth of field (DOF): how much of the image is acceptably sharp/in focus from the foreground to the background. f/4 with have a small DOF which can be used to produce and image that is sharp in the foreground and blurry in the background. f/22 can be used to get sharp details all the way from the foreground to the background.
trade-offs for different aperture settings: Each lens has an aperture setting that produces the sharpest images. It is often somewhere around f/8 but depending on the scene this may not produce the result that you are looking for. Aperture settings above f/16 on high end lenses and f/11 on lower end lenses will produce diffraction of light which results in poorer quality images. However, an aperture setting of f/22 may be needed to get the needed DOF. It is just important to know that you will have to sacrifice either image quality or depth of field.
3. ISO: How sensitive the camera's sensor is to light. Settings are 50 (only some camera's), 100, 200, 400, 800, 1600, 3200. Anything above 3200 will be really poor quality even with the best camera's. 50 will give you the best quality image with the most detail and the least noise. However, it will also result in the slowest shutter speed. ISO 3200 will give you the worst quality and the most noise, but will result in the fastest shutter speed.
How ISO effects shutter speed: lets say that an ISO of 50 results in a shutter speed of 1/100 of a second, if you increase the ISO to 100 then the shutter speed will then become 1/200 of a second, ISO 200 will increase the shutter speed to 1/400 of a second, ISO 400 to 1/800s, ISO 800 to 1/1600s and so on. Essentially, increase the ISO by 1 stop (50 to 100) and you will increase the amount of light entering the camera by 1 stop resulting a a shutter speed that is 1 stop faster (1/100 to 1/200 sec).
4. My approach:
I shoot in aperture priority (Av) mode which allows me to change the aperture depending on the scene that I am shooting. I often shoot between f/11 and f/16 to get the most depth of field and detail in the image. I then choose my ISO setting to get the shutter speed that I want.
For this image it was important to have a large depth of field (DOF) in order to get everything from the flowers to the mountains in acceptably sharp focus. Therefore I used an aperture of f/16. I was lucky that the wind died down and allowed me to shoot this image at ISO 100 and a shutter speed of 1/8 sec. If the wind had been blowing I would have had to increase to ISO to maybe 800 to get a fast enough shutter speed to freeze the flowers.
For this image there was nothing in the foreground that needed to be really sharp so I used an aperture of f/11. I wanted a long enough shutter speed to smooth any ripples in the water. I set the ISO to 100 which gave me an exposure of 1 second and it gave me the result I was looking for.
I hope that you enjoyed my first blog post. Please feel free to e-mail me with any further questions.