On Mar 25, 2005, at 3:08 PM, Alan Chan wrote:
AKAIK, most manual focus Pentax lenses are rather simple in design and there are
basically only 2 things to calibrate - the front and rear group distance & the
focus. Everything else is pretty much fixed and determined by the precision of
machining in the factory, including the optical axis. However, not all lenses have
such design. The Tamron for instance, I have the impression that they are prone to
misalignment because the optical axis is adjusted through a set of screws on the
inner barrel. It is not uncommon for new SP28-75/2.8 has such issue out of box.
They also have pieces that all screw into place.
Small adjustments to thread seating are made by technicians hand assembling a lens. The guy who does repair work for me always checks with a collimator after cleaning a lens and reassembling it, and I trust his judgement as I do not repair optical assemblies myself.
Godfrey
