focus shift???

could someone tell me what focus shift means when it is used in context with a T urner Reich Triple Convertable? also, are these lenses coated? thanks

When converted, ie used with only one of the lens cells, the focus will shift away from the film plane as the lens is stopped down from wide open. When the lens is used with both of the lens cells in place this does not happen. It has to do with the lens formula changing with only one element being used. Focusing should be done with a filter in place (this can also affect the focus) and with the lens stopped down to the taking aperture. As to coating, I doubt it. Mine were patented in 1917 and 1895.

Even some of the Dagors show a little focus shift as you stop down, hence the need to focus at the taking aperture, although as previously stated, some T.-R.'s will show this more markedly than others. Qulaity varied from lens design to lens design and sometimes from lens to lens. Some of the T. -R.'s have 10 elements, rather tricky to center and so forth in the old days.

Coating did not come in to common use until after WWII. Many of the T.-R.'s out there are from the 20's & 30's and before. Bare in mind, patent dates don't necessarily reflect production dates. The Winchester '94 has been in almost continuous production since it's patent, 1894....