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Author Topic: FOV Equivalences vs Magnification  (Read 63946 times)


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FOV Equivalences vs Magnification
« Reply #80 on: April 14, 2008, 10:27:10 AM »

... if one considers 50 mm to be normal, then a 300 mm is a 6X power, a 400 mm is an 8X power.  So when I mount a 300 mm on a 1.5x crop body, it is still a 6X---nothing changed except that we now call it the equivalent (same as) a 450 mm.  Basically we are cropping and "blowing up" or enlarging the image.[a href=\"index.php?act=findpost&pid=186939\"][{POST_SNAPBACK}][/a]

I was just wondering if, for all intents and purposes, while in the field and shooting wildlife, a 300 mm on a crop body would be the "same" as a 450 mm on a FF body ...[a href=\"index.php?act=findpost&pid=186939\"][{POST_SNAPBACK}][/a]
Yes, it would.

Ummm ... with one exception we can argue about as to what's the significance for practical intents and purposes: The 300 mm lens, used on an APS-C-format body, will produce 1.5 as much DOF as a 450 mm lens, at the same aperture, used on a 35-mm-format body. This corresponds to approx. one f-stop worth of DOF difference. When keeping everything else equal then stopping down by one stop will increase DOF by a factor of 1.41; two stops will double DOF. However one stop's worth of DOF up or down will hardly make a significant difference in an image's visual impact and appearance, usually.

So when shooting from the same spot, a 300 mm lens used on an APS-C-format body at f/5.6, for instance, will produce the same angle of view, the same field of view, the same perspective, the same visual impact, and the same (more or less) DOF as a 450 mm lens on a 35-mm-format body at f/8 (or actually at f/8.7, to be finicky---multiply the crop factor with the aperture number).

And then there are a few more subtle differences ... but those have no significance for most practical intents and purposes. Well---except that a 300 mm lens will be shorter, lighter, easier to carry, and cheaper than a 450 mm lens of the same lens speed  

-- Olaf
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