Lens focusing

[Moto-Uno]

Owning a couple of Moskva-5s and a retina 111c I'm curious about the pros & cons of the front element focusing vs the entire lens assembly being moved.
They both seem to take good pictures,(or is it the film acreage that keeps me satisfied with my ex commie camera?) Any lessons in optics would interest me.
Regards,Peter

 

[wolves3012]

The man to ask for a definitive answer would be Brian Sweeney. As far as I understand it (and I may be in error) the pro for front-element focussing is that the whole lens assembly doesn't move, so it simplifies the focussing mechanisms. There's no need for complicated linkages to a moving iris, for instance. Primarily, of course, that reduces cost.

The con is that it is not as accurate, optically and also gives a more limited focussing range. Moving the front element changes the focal length in addition to altering focus, so you have to keep it limited otherwise the errors get too great.

 

[Sonnar Brian]

I'm not in favor of it, and an optical compromise is made for the lens to be front-cell focus. In practice, with lenses of moderate aperture- I doubt anyone would notice a difference.