> > 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.
