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What is Focal Length?

By March 14, 2011

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Focal length is one of the more important photography terms. The actual mm rating (such as 70mm or 300mm) on your camera refers to the distance from the front glass to the point of focus. Focal length tells you how much magnification is possible for your camera lens.

In practical usage, the larger the focal length, the more magnification the lens produces. (Gallery of example images at different focal lengths)

For point and shoot cameras, the notations such as "10x" or "15x," relate to focal length. Even a camera that says "15x" has a lens with an actual zoom range just like the larger SLRs. If you look in the technical specifications of the camera, there will be a listing for the lens strength equivalent to an SLR lens. For example, a camera with "15x" marked on the box might actually have a 21mm-315mm lens. The 15x refers to the multiplication of the smallest number of the lens (widest field of view) to get the strongest magnification the lens is capable of recording. Another camera with 15x on the box might have a 35-525mm lens. Unfortunately, there is no way to tell what the 15x actually translate to until you read the technical specifications on the lens.

Comments

February 12, 2012 at 8:11 am
(1) Jon says:

Finally – someone who actually tells me “what focal length IS” instead of the significance of focal length. BUT, I have a question…

Your article says “The actual mm rating (such as 70mm or 300mm) on your camera refers to the distance from the front glass to the point of focus”

By “the point of focus” I assume you are referring to the camera film or camera sensor?

Thanks for this – it was a relief to find the answer to my question :O)

February 13, 2012 at 7:52 am
(2) Photography Guide says:

Glad to be able to answer your question Jon. Yes, the point of focus is usually the film or sensor. It is defined as focal point because things like extension tubes can modify the distance to the film/sensor. Hope that helps clear things up!

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