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p.9 #1 · p.9 #1 · Pre-order: Sigma 35mm f/1.4 DG DN Art ($899) | |
tsdevine wrote:
From Automate.org:
Stepper
Stepper motors have an internal rotor that is influenced by external magnets. After a winding effect produces energy, the teeth of the rotor turn in fixed steps. Because of their incremental movement, stepper motors offer utility as they can change speed and direction.
Linear Motors
As the name suggests, linear motors can be thought of as an unrolled brushless motor. They are designed using the same underlying magnetic theory, but they operate in an open form. One major benefit of using a linear motor is speed.
Rotary motors (plus rotary-to-linear devices) versus linear motors
When choosing between rotary motors or linear motors, be sure to clearly define your goals. The two main considerations should be speed and accuracy, but cost can play a major factor. Linear motors can have substantially greater upfront costs.
I don't know how to "confirm" this beyond a shadow of a doubt though. I'm sure there can be better and worse stepper motors, and better and worse linear motors. But as a category, there must be some tangible benefits of one vs the other, especially if there is a difference in cost. Seems like a more expensive solution would need to yield tangible benefits.
-Tim...Show more →
For the focus motors it seems there are a couple speed terms that get interchanged and confused. The first is how fast the motor can slew from min focus to infinity and back. The second is how fast the control system in the lens can accept focus commands.
From my perspective, not verified by testing, it seems like the 135 GM and 85 DN can slew faster than the 35 GM. But it makes sense the GM lenses will be able to accept focus commands faster because of the tight engineering integration an all sony system can achieve and that being a design goal for the new lenses.
I wrote some control code for a stepper motor, and one nice thing about those is you can specify how many steps you want to move. I don't know if sony has any indexing in their linear motors, so the system knows how far the lens actually moved, or if all feedback is via the image on the sensor. In some ways the image being good is really the only thing that matters and what the lens position is doesn't matter, but it seems easier to calculate where the lens needs to be if you know current location and get some info on needed movement based on the phase detection from the sensor.
When Sony first talked about the linear motors they said the benifit was from extra thrust the motors could provide to accelerate heavier glass.
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