One lens, two diaphrams

December 2016 issue Tech

Why would a lens have two diaphragms with one marked in f-stops and the other in T-stops? And what’s the difference?Whether it’s marked or not, every lens has a T-stop value. The formula used to calculate f-stop values is f-stop = focal length ÷ diameter. It treats the lens as a simple hollow tube and doesn’t account for the lens elements inside.A lens element’s shape and composition control the way it refracts and bends light, as do the groups in which elements are arranged, the... Continue Reading >

Velvety Smooth Trans Focus lens

December 2016 issue Tech

And now for something truly different: The Venus Optics Laowa 105mm f/2 Smooth Trans Focus Lens has two diaphragms, one marked in traditional f-stops and the other in T-stops. It differs from most modern lenses in its lack of mechanical and electrical connections between the camera body and lens, which means that not only is it manual focus, but the camera body and lens exchange no electronic information about aperture or focus distance settings. It even lacks automatic aperture return, the... Continue Reading >