A brief word of explanation on what a "fast lens" is. In order to take a picture, you have to allow light to pass through your lens. Light passes through your lens when you press the button on your camera and open the shutter. The amount of light that passes through the lens depends on two things -- how long the shutter is held open and how wide the shutter opening is. If you can open your shutter very wide, you don't have to keep it open nearly as long to get the same amount of light into the camera.
When someone tells you that a lens is a "50mm f/1.8" or a "100mm f/2.8," they are telling you two things. The first number is how far it is from the front of the lens to the film or digital sensors (50mm, 100mm, etc.). That number is not important for this discussion. The second number tells you how far you can open the lens. The lower the number, the wider the lens opens. So, my f/1.8 lens can open wider than my f/2.8, which opens even wider than my f/5.6.
Shooting in low light presents a problem -- camera shake. Suppose I want to take a shot at night. At night, there might not be much available light to take a shot. If I want the subject to be visible in the final picture, I need to get more light into the camera. But how do I do that? Well, one way is to open the lens as wide as it will go. However, suppose you've got it open as wide as it will go and you *still* don't have enough light. Well, the next solution would be to increase the amount of time that the shutter is open. So, instead of holding the shutter open for 1/50th of a second, I'll hold it open for 1/10th of a second.
The problem with that solution is that my hands shake. If you hand-hold a camera and keep the shutter open for 1/10th of a second (or longer), you are going to notice that your image is blurry. The longer you hold it open, the worse the "camera shake" becomes. The only other option* is to get a lens that will open wider. A f/1.8 lens is pretty wide, so I don't have to keep the lens open nearly as long as I would with my f/2.8 (or f/5.6) to get the same shot. Since I can shoot faster, the lens is called a "fast lens."
Anyway, so I bought the 50mm f/1.8 lens a few months ago. This shot, of the Empire State Building (shot from across the street) is one of the first shots I took with that lens. This shot would have been much more difficult with some of my other lenses.
|From Wolfish Musings Pictures|
Canon XSi, 50mm lens
As always, critiques, comments and criticisms are welcome and encouraged.
Statue of Liberty
Trinity Church, September 11, 2008
* Yes, you can bump up the ISO rating too. However, I don't want to get too technical -- this is a very basic description of a fast lens.
Great photo. I'm jealous of the camera. I have a fair number of shaky night shots, and my hands are fairly steady.
It's worth noting that if you get an IS lens, you can effectively get another one or two f/stops out of it due to reduced camera shake. (You can keep the shutter open a lot longer without much ill effect.)
I have a really nice night-shot I took with a surprisingly cheap digital camera that has optical IS built in (as a lot of them now do). A shot like that would have been impossible without an expensive SLR with an even more expensive fast lens just a few years ago, before IS came down in price.
(Nice shot, BTW!)
Thanks for the education, i never realized that about night shots. And you did get a nice picture.
I've done a lot of night shooting, including a fair number of shots where eposure time is 15s not 1/15s. good tripod is a livesaver!
very nice photo!
I dont think I have seen a better shot of the Empire State building. Nice shot.
You really do have an eye.
Off topic, but have you noticed the kinds of webads you have now?
God Loves You
Here is a Prayer That Can Change Your Life
Why is the rapture a lie?
Jesus Christ will return to rule earth with the resurrected saints.
And at the top, you have a banner saying, "Knowing how to know/Scientology Video Channel"
Very cool. Good composition, the black/white gives it an atmospheric, period feel. Commendably sharp and well illuminated.
Thanks for the heads up, MD. If you find any other offensive ads in the future, please let me know of them (with the URL) and I can have them blocked.
Thank you everyone for the comments and critiques.
I've had great results using a Canon 85mm/1.8 lens (vintage around 1970) with my old SLR film camera. The longer focal length at this speed makes focusing easier, tightens the composition, and keeps extraneous background elements out of the frame while maintaining a natural perspective. It's especially good for portaits of children and adults.
Thanks for the comments. Please forgive the ignorance, but what is an s/b portrait?
s/b = "should be"
I was correcting the misspelling in my previous comment!
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