Hi, Does any one know the details of the shifting of focus in macro/closeup as a lens is stopped down? I've heard that the xenars do this ... you have to refocus at stopped down aperture.This is a pain because the image is so dim at f22-32 e tc....any solutions? Does the focus shift move closer or further from the film p lane when stopped down? Thanks, Emile.
Hi, I've read what Ansel Adams wrote about that, he mentions the Dagor and similar lens designs. But never heard about that shifting as shooting with Tessar-types nor made any such experiences with that lenses.
As far as I know, the main lenses that suffer from focus shift are Dagors, dagor-related lenses and Imagons. These lenses all have significant spherical aberration, intentionally in the case of the Imagon. The Dagor, Angulon and Super Angulon are discussed in Rudolf Kingslake's book A History of the Photographic Lens. Kingslake's diagrams show the Angulon (patent 1930) to be what he calls a reversed Dagor. The Super Angulon (patent 1957) is an unrelated design.
My suggestion for testing whether your lens has focus shift in closeups: focus on the filament of a clear-glass lightbulb, perhaps using a dimmer. Then stop down, turn up the brightness, and recheck the focus. If it is a problem, in the studio you can try using extra illumination for focusing. In the field, sometimes placing a flashlight as a focus aid is possible.
Thanks much for the info....Good Light! Emile.
Posting Permissions
Reply With Quote
Bookmarks