Find it: Website with a unique explanation of lens focal lengths.

December 24, 2008 6:46 AM

Find-that-website filter: Website with a unique explanation of lens focal length with respect to photography and zoom lenses.

This page explained lens focal length and related it to viewing a very large 2-D print of a scene from different positions in the room. Moving closer, further back, etc., with the point that zoom lenses aren't really zooming into the picture so much as they're cropping, or something along those lines.

posted by odinsdream to science & nature (7 comments total)

This page lets you see the same seen through different focal lengths...
posted by zachawry at 6:52 AM on December 24, 2008

As I recall, the relationship between the camera and the scene remains unchanged, just magnified. The perspective will be the same. It is like cropping in a way.

Neat page zachawry
posted by raildr at 7:23 AM on December 24, 2008

There's a similar tool for Canon focal lengths.

It's also worth noting that that's not really accurate, because zooming a lens is not the same as cropping, if the thing you're taking a picture of is a 3D scene and not a flat picture. Lenses at different focal lengths exhibit different depths of field, perspective and barrel distortion, and other visual artifacts. Also, notably, the focal length of the lens is also directly tied to handheld motion artifacts - any motion of the camera is significantly amplified by a longer lens. Focal length of a long zoom may also affect your choice of widest aperture.
posted by Caviar at 7:34 AM on December 24, 2008

There's some discussion of the effects of focal length sprinkled throughout John Hedgecoe's New Manual of Photography (still the best general reference I've found for the technical aspects of photography), but I've never seen it comprehensively covered on a website anywhere.
posted by Caviar at 7:44 AM on December 24, 2008

Thanks - this was more than an interactive tool. I seem to remember it being a quite-lengthy technical explanation that used the mental image of standing very close to a very large 2-D print as an analog to using a large focal length to capture a scene.
posted by odinsdream at 7:44 AM on December 24, 2008

How about this blog post?
posted by kirstk at 8:48 AM on December 24, 2008

kirstk; that's closer! I think the page I'm looking for included some diagrams and photos, too.
posted by odinsdream at 9:24 AM on December 24, 2008