M Lens Focus Breathing

[robb]

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Which M lenses have the least focus breathing for use on cine?

modern asph designs?

1980-2000 designs?

older classics?

Thanks for any thoughts.

Robb

[adan]

Well, the term "focus breathing" has been used confusingly to mean two opposite things - but assuming you mean "lenses without focus-breathing do NOT show FoV changes as they focus closer or farther"- probably no M lenses at all.

It is well-known, for example, that unit-focusing lenses (all the elements move together as one unit) change the field of view the more they are extended. And the "fixed-area" M framelines make this obvious. The lines are only perfectly accurate at one focus distance (which has varied over the decades, but is currently 2 meters/6.6 feet).

As I documented when questions arose at the intro of the M10. Example pictures made with the 75mm APO-Summicron-M. This lens clearly "breathes" when focused at different distances.

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Most lenses that avoid focus-breathing use internal focus - the lens overall does not move or change length, just the glass elements inside, sliding around relative to one another. The SL lenses being an example (and quite possibly the S and Q also).

But internal focusing does not work with the M's rangefinder system - which counts on the total movement of the whole lens and its RF cam, to align the double-images in the RF patch. So M lenses do not use internal focusing.

At most they have slightly-moving "floating elements" to improve image quality (not size/magnification) when focused close.

OTOH, wide-angle unit-focusing lenses move LESS than long focal lengths. And therefore the wider the lens (18-24-21mm, or the "zoom" 16-18-21), the less focus breathing will occur.

A 21mm unit-focus lens may only move a couple of mm to focus all the way from infinity to 0.7m (changing the field of view, or "breathing," only slightly), while a 135mm may move (and "breathe") ~10 times as much.

Edited 7 hours ago by adan