Physics: Why exactly does a large aperture make the background blurry?
Hey guys,
I love portrait shots and often have my Canon EF 50mm f/1.8 set to a low f value (around 2.2). I know this gives me wonderful portrait shots with the subject in focus and the background blurry and all bokehry (I know, I'm making up words!). But I've often wondered.... WHY?!? Why is it that widening the hole in a lens and allowing more light through makes the background nice and blurry? Is it to do with more light coming through or is it to do with the reduced exposure time? I suspect it is the former. When more light comes through, is it scattered in a different way?
Can anyone explain this to me? I'd just be super interested to know... there must be someone who knows or has done physics before... or is much better at using Google than me ;-)
Hope you can help!
JSL
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I would hugely appreciate your comments on my pictures: http://www.flickr.com/photos/scott-lee/
Body: Canon EOS 450D (Rebel XSi)
Lenses: Canon EF 50mm f/1.8 II; Canon EF-S 17-85mm f/4.0-5.6 IS USM
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