Turn dual-focus into single-focus?

[Caleb Genheimer]

Hi, all! Let me preface this by stating that I'm no optics or lens expert, just a guy with a idea.

 

But I've been wondering . . . is it possible to turn dual-focus anamorphic setups single-focus by setting the two lenses to infinity and simply moving them closer or farther away from the sensor? Could the dual-focus challenge be solved by a variable-length lens mount adapter with a nice built-in helicoid?

[Gábor Ember]

No, that will only change the taking lens' focus, not the anamorphic. What you say is what the most basic lenses actually do when focusing. Take a Helios for example. When you turn the focus ring, the whole lens block moves closer or farther thus the anamorphic mounted in the front of it does the same.

 

The most simple anamorphics focus by moving only the front lens group while the back lens group stays in place. Oh and at least on my Sun anamorphic the focus is the other way around (Sankors and the like are almost the same as far as I know):

the Helios has infinity focus when closest to the sensor

the Sun anamorphic is at infinity when the front glass is farthest from the back glass