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[quote name='IanCD' timestamp='1305757190' post='8560']

Thanks Markus,

So that's about 2 stops (does it stay more or less constant?)

Which would have a detrimental impact on (shallow) DoF except that DoF gets shallower with increased focal length... so do the effects cancel each other out..?

[/quote]

Mmm, not really - it's easier to think of it as of narrower field of view instead. You have 1.5x narrower FOV - it means you have to step back to get the same framing - DOF increases correspondingly. Being a bit of nit-picker I have to point out that it's slightly more than one stop (~1.08 stop for Nikon and ~1.14 for Canon) but the difference is rather marginal, so let's say it's one stop.



Actually, 85mm f/1.8 performs exactly as 135mm f/2.8 on Canon <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' />



Edit: I see that Brightcolours already calculated that <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/laugh.gif' class='bbc_emoticon' alt=':lol:' />