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C300 Mk III and auto Iris

Rising Star

While I'm still in the "get acquainted" phase of my relationship with the C300 MK III, I've been thumbing through the manual—yes, I've printed it out and have it mounted in a looseleaf binder—I came across an option for AUTO IRIS.  But it appears that auto iris is not available with EF lenses, or with certain EF lenses, but is available with cine lenses, and I have not been able to find an explanation for that distinction.  I really have no use for auto iris, but I would still like an explanation.  Anyone care to chime in?

Thank you in advance,




I believe it has something to do with apertures being "de-clicked" in cinema lenses.  i.e. you get a nice smooth transition from one aperture to the next.  Versus jumps you get when adjusting apertures on lenses designed primarily for photography.


Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers

Hi Ricky, and thank you for your reply.


EF lenses have no aperture rings, so there is nothing to click or, for that matter, de-click. Furthermore, most, if not all FF and MF cameras (Fuji GFX, for example.  All GF lenses have clickable aperture rings, and the camera can automatically set aperture) offer auto aperture setting even with lenses that have clickable aperture rings.  So I suspect that there is another explanation.


BTW, it seems that we are the only two people posting to this forum in recent times.

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