Photography : What do focal lengths mean? Focal Length v Zoom?

Today I found this great little image which I feel I really must share.

It explains focal length and what different camera lenses see.  For me me this was quite tricky to get my head round but it was explained perfectly to me in the following way.

Our eyes see things, in focus, with a lens equivalent of 50mm (and an approximate field of view of 50 degrees – the mm focal length of the lens and degree of field of view although the same are not related).  Our peripheral vision picks up more (a lens equivalent of  about 10mm), but the actual in focus part of the world we see is captured at an equivalent of 50mm.

The following images shows what each lens will capture in relation to what we see…

This is our view of a beach.  It incorporates about 130 degrees of a field of view and represents our entire vision (although in reality the periphery will not be as focused.)

Field of View of the Human Eye - approximately 130 degrees
Field of View of the Human Eye – approximately 130 degrees

This is how different camera lens will frame this image dependant on their focal length.  The higher the mm value the closer we get in to the light house in the far distance.

Field of View Vs Camera Lens View - this is the view of the same beach that each lens takes from the same scene.
Field of View Vs Camera Lens View – this is the view of the same beach that each lens takes from the same scene.

As you can see the 14mm pics up the image closest to our entire field of view and as the focal length increases the smaller the field of view becomes and the closer to the lighthouse we get.

For me this photo was brilliant, I never really captured how the camera focal length affected the picture but this helped me massively, hopefully it helps someone else also.

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