I think Matthew explained it pretty well. When you "focus and move" what you're actually doing is rotating your neck, describing an arc, so that causes a slight change in distance between the sensor and your new wish-to-be-in-focus point. This is especially noticeable if you focus on a subject's nearest eye then reframe. The arc you move through is significant if you are within a few feet of the subject, eg with a headshot using a 50mm-e lens or less, and especially with wide-open apertures. It's not so bad if you are standing 12 feet away with a 200mm-e.
When I'm shooting subjects at f8 with the 50-135 I can always center-focus and reframe with no ill effects. I do not do that at f2.2 with the DA*55 shooting close-in (head and shoulders). Guaranteed fail. I move the focus point and carefully focus on subject's eye. On Fri, Aug 16, 2013 at 10:19 AM, Aahz Maruch <a...@pobox.com> wrote: > On Wed, Jul 24, 2013, Bruce Walker wrote: >> On Wed, Jul 24, 2013 at 8:05 PM, David J Brooks <pentko...@gmail.com> wrote: >>> On Wed, Jul 24, 2013 at 7:15 PM, Aahz Maruch <a...@pobox.com> wrote: >>> >>>> Let me rephrase: does anyone actually use manually-selected AF points for >>>> handheld shooting? >>> >>> I use the single centre and recompose >> >> That doesn't work with large apertures and short teles or longer. It >> becomes auto-defocus then. > > That doesn't make sense. Can you explain further? If you pick your > focus point, half-press shutter (or lock focus/exposure), move the lens, > shoot -- where does the defocus come from? I've certainly shot plenty > that way. > -- > Hugs and backrubs -- I break Rule 6 http://rule6.info/ > <*> <*> <*> > Help a hearing-impaired person: http://rule6.info/hearing.html > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. -- -bmw -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
