On Sat, Sep 16, 2006 at 04:16:42PM -0400, Mark Roberts wrote: > John Francis wrote: > > >On Sat, Sep 16, 2006 at 01:28:26PM -0400, Mark Roberts wrote: > >> Ryan Brooks wrote: > >> > >> >Adam Maas wrote: > >> >> At f2.4, the 70 is about perfect for me. Essentially the same length > >> >> and > >> >> speed as the legendary Nikon 105 f2.5, which is a superb portrait lens. > >> >> > >> >You are getting more DOF with the 70mm though. > >> > >> Not true. Not at the same subject magnification, anyway. (And that's > >> what you'll be doing if you compare both lenses as portrait lenses.) > > > >Actually, Mark, Ryan is right. > > > >A portrait taken with a 105mm lens at f2.8 on a full-frame camera will > >have a shallower depth of field than the same portrait (taken from the > >same spot and enlarged to the same size) > > Right. But I specified "same subject magnification", not "taken from > the same spot". And "same subject magnification" is pretty much how > everyone does portraits: You frame as a head shot, waist-up, 3/4 or > full length and compare two lenses with this view. I've never heard > anyone saying. "Well this Lens 1 has shallower depth of field with a > head shot than Lens 2 does with a 3/4 shot": It's not a meaningful or > useful comparison.
The two situations I described (105mm lens on a full-frame camera, 70mm lens on a 1.5x crop factor camera such as the Pentax DSLRs) will have exactly the same framing - both will be, say, head-and- shoulder shots if taken from the same point. *That*'s how most people do portraits - you frame the shot to use the entire area of your viewfinder. And the full-frame camera will have less DOF on that head-and-shoulders shot than the small-sensor camera will have with an image framed exactly the same way. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
