This week was the first class of my six-week "Seriously Fun Photography" class. So what did we cover?
We learned that to control exposure, we need to work with three related elements:
This is the ISO "speed" of a digital sensor or of film. ISO 100, 200, 400, 800, 1600 and 3200 are available on many cameras (but not all), and you should take some test shots with yours to find out if the higher ISO settings are usable or not. Figure out the fastest ISO speed you find produces acceptable shots on your camera -- you'll need to switch to it sooner or later. Notice that each ISO speed is twice as sensitive (or half as sensitive) as the next.
The f/stops to memorize are f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. If you forget these, make two columns, and at the top of the left one write 1.4 and at the top of the right one write 2.0. Now double each number as you go down the column (rounding off when needed). Changing one stop lets in twice as much light (or half as much, depending on which direction you go. f/2 lets in a lot of light, f/22 lets in very little light. So if you took a picture using f/8 and it seemed a little too dark, you would switch to f/5.6. If you took a picture using f/8 and it seemed a little too bright, you'd switch to f/11.
The common shutter speeds are:
1/1000th of a second
-- As a rule of thumb, if you are moving and you're subject is moving, you'll want to be shooting at 1/1000th of a second to get a sharp picture.
-- If you are still but the subject is moving along, it would be good to be at 1/250th or faster.
-- If you and the subject are both relatively still, you can probably handhold the camera as slow as 1/60th, but slower than that and you'll get a soft picture because of camera shake caused by pressing the shutter.
-- At speeds that are slower, you'll need a tripod to steady the camera, and probably want to trigger it using the self-timer or a release.
-- Many decent cameras have higher shutter speeds, and these are very useful for action or sports.
Notice that the relationship of these shutter speed settings is also doubling (or halving) the amount of light that hits your sensor.
So, from a technical standpoint, as we approach any photo situation we'll want to decide on an ISO setting, a shutter speed and an aperture. The three are interrelated and all use a doubling / halving system so it is easy to calculate how to change them when needed.
We also started considering focal length: We learned that:
-- on a 35 mm film camera, a 20mm lens is very wide, and that on a digital APS-C sensor it is wide.
-- on a 35mm film camera, a 50mm focal length lens feels like it sees about the same as your eye and is considered "standard." on an APS-C sensor as you have on most DSLR cameras, a 50mm lens is slightly telephoto -- very good for basic portraiture.
-- on a 35mm film camera, a 90mm lens is telephoto and would be very good for portraits. on a DSLR it is even longer and works great for making a flattering portrait.
For sports or similar shooting, we'd want to be able to go to 200mm or 300mm in focal length. For some architectural photography, or in other cases where we need to go really wide, we might need to to get something like a 10-20mm superwide zoom.
We found that shooting with a wide-angle focal length (like the 18mm length common on "kit lenses") most space seemed to "expand" compared to what our eyes see. Switch to a telephoto length made the space seem to "compress."
At the end of the class we tried an experiment where we tried making some portraits using our new knowledge of focal lengths. We shot a photo of a person using a wide focal length, standard focal length and telephoto focal length. Then we repeated that but moved our position so that the framing on the person stayed the same in all three shots.