Serene Life

by garik

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2,419 reputation
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bio website imaginaryindustries.com
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visits member for 3 years, 10 months
seen Oct 21 at 16:18

Grumpy.


Oct
21
comment Why are tripods forbidden in some public spaces and how to deal with it?
+1 for air-quoting "steal".
Oct
4
comment What does STM mean on a Canon lens?
I cede the point about DC. There is one type of DC motor: the homopolar motor. However, it's largely a scientific oddity, and not used in many practical applications, and no lenses as far as I can tell. The rest are still AC, though, and that very much includes all types of stepper motors.
Oct
4
comment What does STM mean on a Canon lens?
Further, I'd nitpick about the OP's description a bit. Unless the USM is categorically less effective at focusing, both motors have to have the same degree of precision. I think the difference here is the ability to better control the velocity, which is needed for gradual zooming/focus changes. This is not a function of precision. I'd guess the velocity control in a USM may not be very good.
Oct
4
comment What does STM mean on a Canon lens?
1. A dc motor that does not alternate is either a homopolar motor, or a solenoid. 2. Unipole stepper motors are not generally used, because they cost twice the copper for the same torque, and it's still not DC, because the current is not continuous, and it's effectively using the motor as a autotransformer to reverse the field. 3. I never made any claims about the precision of the motor, but rather was only ever speaking to the whole control system. 4. You can't have a servo system without feedback. Feedback is literally part of the definition of a servo.
Oct
3
comment What does STM mean on a Canon lens?
Oh, also, in the great majority of applications, stepper motors are run open-loop, which means they do not have any position feedback mechanism. The only real reason to ever use stepper motors is to avoid the cost of said feedback mechanism (typically an encoder of some sort). Once you have the feedback mechanism and the corresponding control loop to make it work, a brushed servo motor will almost always outperform a stepper motor.
Oct
3
comment What does STM mean on a Canon lens?
Here is an answer I wrote on the electrical engineering stack exchange site about what, exactly comprises a servo-motor/servo-system/etc...
Oct
3
comment What does STM mean on a Canon lens?
TL;DR You can use stepper motors as a servo motor in a part of a larger servo system. The term "servo" motor has been polluted by RC model community to refer to one specific type of servo system that's commonly used for controlling models, but that's not the only type of servo motor, or servo system.
Oct
3
comment What does STM mean on a Canon lens?
@Travis - 1. ALL motors are AC. "DC" motors just use brushes internally to convert the DC power to AC. Stepper motors however do not have brushes, so you have to externally commutate them. Colloquially, this type of drive is referred to as "AC", since it requires driving current in both directions through the field coils (which is basically AC). 2. I'm using the engineering definition of servo motor. 3. Precision is a function of the complete control loop. The motor type is irrelevant as long as the control loop can compensate properly.
Sep
30
comment How to get photos to be under 500 pixels
Uh...... you do know you can resize images, right?
Sep
24
awarded  Autobiographer
Sep
6
comment How does the iPhone 5s manage to take HDR photos at full-frame rate?
The iPhone doesn't have a physical shutter at all. Very few cell-phone cameras do.
Sep
1
comment Should I expect better results from more expensive variable ND filters?
Are you using a good tripod? If your tripod is flimsy, you could have camera vibration issues for the longer exposures, which would negatively affect the shots with the ND filter.
Apr
18
comment Is it possible to make an image which is only photographable in black or white?
@TFuto - Arguably, the retina can be considered part of the "brain". It varies by neuroscientist.
Apr
13
answered What is the MECHA DEVICE SERVICE in the Sony Alpha 7
Apr
13
comment What is the MECHA DEVICE SERVICE in the Sony Alpha 7
I would assume that it's "mechanical device service", and probably just an internal code for tracking the cost of the labor to do the service.
Mar
17
awarded  Notable Question
Dec
11
awarded  Yearling
Dec
1
comment Is this statement By Jim Zuckerman incorrect?
I'd be a smart-ass and point out that there are electronic shutter systems that are in fact fast enough that they can trigger in the time it takes light to travel to a subject a few meters away from the camera and back, but that's primarily just snark.
Dec
1
comment What is the benefit of the sensor marker?
To answer your second question. It's the same marker pretty much everywhere, and it's on all serious cameras of any make (including Nikon, etc...).
Sep
20
comment How can I completely avoid noise for stock photography with my Canon 650D?
What ISO are you shooting at? Can you post a example picture? Having at lease some noise is normal, it's a inherent part of the way the image sensor works.