Discussion in 'Photography Beginners' Forum' started by JPT, Nov 6, 2007.
What do "18-55mm" and "f/3.5-5.6" mean? What do each do?
18-55mm is the focal length. This lens has a range or zoom so it can change it's focal length.
The longer the focal length, the narrower the Field of View (FOV)...and the more magnification.
A shorter focal length will give you a wider view (wide angle).
The 'F numbers' refer to the aperture of the lens. When listed on a lens or in the name of a lens, it refers to the maximum aperture of the lens. In this case, the maximum aperture also has a range...it gets smaller as the lens zoomes out.
F numbers are a ratio between the focal length and the diameter of the opening in the aperture blades. The lower the F number, the larger the aperture. Read that again and remember it.
Bigger is better, so when looking at lenses, you would want one that has a lower F number like F2.8, F1.8 or F1.4 etc.
18-55 is the focal range of the lens. There are a few different types of lenses but they will all fall into basically 2 categories as far as focal length. Either they are prime lenses and they have a fixed focal length (i.e., 50mm, 105mm, 77mm, etc) and you basically zoom with your feet making the subject larger or smaller by physically moving closer or further away. A zoom lens has a range of focal lengths such as this one and you can bring the subject closer or further away by adjusting the ring on the lens.
The other number speaks to the aperture of the lens. This one has a range of 3.5 to 5.6 as the max aperture of the lens. At 18mm it has a max aperture of 3.5 then somewhere along the focal length it's max aperture is only 5.6 so at the end of the range (55mm) it's max is 5.6. The aperture is the diaphram that opens or closes which lets in more or less light allowing it to strike the sensor or film thus exposing the image. If you take the lens off the camera and turn the aperture ring, you'll see little blades making the hole in there bigger or smaller. Its minimum aperture is probably something like 22 which is very small and lets in very little light.
So why is this important? Depending on the amount of ambient light or flash determines how much light you need to let into the lens to properly expose it (among other this like ISO and shutter speed). In very bright light like mid day outdoor sun, you would want an aperture of probably f/16 or thereabouts. In very low light, like an indoor church setting, you want to let in as much light as possible, so that you can maintain a higher shutter speed. Thus, you would use the lower end of the aperture (smaller number means larger opening). A "fast" lens is one that would typically go to a max of between f/1.4 or f/2.8. Faster lenses are more expensive, especially when you're talking about a wide focal range of like 70-200mm. Those that have an aperture of something like 2.8 which is consistent through out the entire focal range are more expensive still. In that case, they would only report one aperture and not a range (e.g. 70-200mm f/2.8) meaning you can shoot with a max aperture of 2.8 anywhere in the focal range of 70-200mm.
This one you're talking about is probably in the $100 or less range.
as usual, Mike is always quicker
yup, what Mike said.
I've seen some lenses with different letters after the aperture such as "D", "G", "DG" "LD", etc Do these have any significance?
Typically these are designations for something...but each company is different. If you are looking at Nikon lenses, for example, you could look up what the letter mean, on the Nikon web site.
Separate names with a comma.