E-M5 micromanages shutter speed in A mode

Started Aug 19, 2012 | Discussions thread
Detail Man
Forum ProPosts: 14,950
Re: E-M5 micromanages shutter speed in A mode - 2
In reply to Timur Born, Aug 21, 2012

Timur Born wrote:

Detail Man wrote:

Continuous variablilty of mechanical position can only be accomplished by a complicated, full-blown motor-controller - whereas I think that it's likely that stepper-motors would in all cases be the most likely implementation in these small, limited-component, limited-power, limited heat-dissapation, limited production-cost camera systems.

How smooth looking would a stepper-motor be? If you put a 45/1.8 on the E-M5 and start video recording with fixed time + variable aperture (S, P) then the movement of the aperture is visibly smooth. The 45/1.8 allows to take a very good look at the aperture and during active video recording the usual "Rattlesnaking" of quickly stepped aperture movements turns into butter-smooth silent movement.

I guess a stepper-motor could do it, too, given the already small 1/3 EV steps? But I frankly don't know.

As I said, without the use of a stepper-motor, any motor driven system has to also incorporate an entirely separate position-sensing system in order to provide a feedback signal to a high-gain servo system, vastly complicating the system in every way (accuracy, complexity, reliability, expense, etc)

See Section 10 (on Page 182) of this document:


for a description of the stepper-motor system that controls the aperture blades in Canon EF lenses.

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