What Does Speed Mean?
Common question: "What is speed?"
Photographers aren't always the best at, well, talking about photography in a clear, universal, and understandable way.1
- Lenses are described as fast
- You have a fast and slow shutter speeds
- You have a fast or slow camera
- Film is rated at different speeds, and your digital image sensor can be set to different speeds
- Flashes have recycle duration, fast or slow
- Your memory card is rated at different speeds
Let me break it down. There are three ways photographers use the term "speed" or "fast".
The first is correctly, when talking about the amount of time things take. Like the memory card rating. Faster memory cards transfer data... faster, and a camera that is considered 'fast' by a sports photographer may mean there is very little delay between pressing the shutter button and taking a photo.
The second is as a label. The shutter speed may be called "speed", as in "What speed are you at?". Don't talk like this, it's confusing. It happens, but don't be part of the problem. Refer to the shutter speed as "shutter", please. Thanks. The speed of film is another one, and I also recommend not saying "speed", and refer to the "ISO" instead. KTHNX.
The third is amount of light. Instead of 'speed', you will probably hear 'fast'. A "fast" lens is a lens with a very large maximum aperture, that lets in a lot of light. This term isn't going away, so get used to it. Don't, however, refer to a lens as "speedy". As in "That canon 85mm f1.2 sure is speedy!". Because that's a $1900 lens and I don't want it, as in the object, to be speedy, as in "fell off the camera while shooting out the window of a car on a highway", ever!
The fourth is percentage of light. Lenses always "eat up" a little bit of light. If lenses let a perfect 100% of light through them, then they would be invisible. Nowadays, lenses are damn good2, so you won't hear this term very often. You had t-stops instead of f-stops to help this calculation. But previously, lenses ate up enough light that you had to factor this into the exposure. "Faster" lenses ate up less light.
So here is is again. If you hear "fast" it means amount of light (wider aperture) or a quick shutter speed setting. If you hear "speed" it actually means time, or is a label for a setting.
Hope I cleared things up, it's not actually that bad. Just don't forget that photographers are also, frequently, bad at grammer and will mess these things up anyway. They are also likely to be consistent, as an individual; so you can learn their unique grammar and parse everything just fine. Don't be rude to them, since there is barely anything considered "correct", and if you are confused, politley ask for them to clarify.
1. I am an obvious and brilliant exception. ↩
2. Citaton Needed. ↩