I've never really noticed any back/front focusing issues, but you folks are making me paranoid. Is there a good kind of shot for testing this? I'm thinking of using the 50 1.4 and 135 2.8, wide open, to take a portrait and using the central sensor to focus on one eye? Will this be a good indicator or would other conditions be better?
>>> mike wilson <[EMAIL PROTECTED]> 2/25/2008 3:53 PM >>> A better way of saying what I was trying to.... > > From: Paul Stenquist <[EMAIL PROTECTED]> > Date: 2008/02/25 Mon AM 11:26:58 GMT > To: Pentax-Discuss Mail List <[email protected]> > Subject: Re: K20D & back focus > > I think it's more likely that the sensor's focus plane is more > accurate rather than tighter than that of film. The focal point is > the focal point. And since film is somewhat curved, it can never be > totally accurate. > Paul > On Feb 25, 2008, at 3:58 AM, mike wilson wrote: > > > > >> > >> From: "Bob Sullivan" <[EMAIL PROTECTED]> > > > >> Reading the promo literature on the K20D, I noticed a new feature. > >> The camera has the ability to store adjustments for backfocus (or > >> forward) for 20 lenses. > >> The claim is that all the DA lenses are fine, but others may need > >> adjusting. > >> > >> Any ideas on why this might be? > >> Do some lenses transmit more of the right wavelength light for > >> focusing? > >> I am puzzled as to the physics/mechanics of this. > > > > I am beginning to suspect that the focus plane required for sensors > > is much tighter than that for film and that lenses that would have > > been fine on replaceable medium do not now have the quality control > > required for good focus. Combined with an uncertain condition due > > to age and wear and tear, it may be that many lenses do not have > > the ability to focus properly on the sensor. This will of course, > > mean that it is individual lenses (although there may be model > > traits) that require to either be adjusted to suit the sensor or > > have the sensor placed into a suitable position. As the sensor can > > be easily adjusted to compensate that seems to be the logical > > suggestion, rather than a major service on each lens - which would > > then only make them suitable for one particular body. I'm not sure > > which is Mo' and which is the mountain in this scenario. > > > > I also still can't work out why one lens should appear to focus > > properly in the viewfinder yet not on the sensor and another > > focuses fine on both. > > > > > > ----------------------------------------- > > Email sent from www.virginmedia.com/email > > Virus-checked using McAfee(R) Software and scanned for spam > > > > > > -- > > PDML Pentax-Discuss Mail List > > [email protected] > > http://pdml.net/mailman/listinfo/pdml_pdml.net > > to UNSUBSCRIBE from the PDML, please visit the link directly above > > and follow the directions. > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. > ----------------------------------------- Email sent from www.virginmedia.com/email Virus-checked using McAfee(R) Software and scanned for spam -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. !SIG:47c32dc069101956845059! -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
