kidtexas wrote: charles.K wrote:
My understanding the chrome/brass or titanium versions have very little if any focus shift.
That always sounded like internet bologna to me. If it\'s the same optical design, it\'s the same optical design.
That being said, it\'s possible that some of the lenses had their focus calibrated so that the focus shift was hidden better by DOF at various apertures. Like with the ZM 50/1.5 being calibrated at f/1.5 or f/2.8.
None of us have tested enough samples to make a statistically valid comparison, but enough of us have seen the same result that I don\'t believe it is bologna. Mine is chrome, and has little, if any, focus shift. The two black copies I have tested had noticeable focus shift.
Keep in mind that there is a possible physical reason for this. The chrome and titanium versions are made of brass (you can chrome aluminium), which is very easy to machine, whereas the black copies are made of aluminium alloy, which is much harder to machine accurately.
There are certainly good black copies out there. I have not yet heard of a bad chrome or titanium version, but that could be coincidence.
