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04-21-2008, 04:01 AM   #1
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In-body SDM?

I don't know to what extent this is possible, but couldn't Pentax use ultrasonic motors instead of the classic type, for in-body AF?

The aim would be to reduce AF noise most of all. I don't much care about AF speed, but I'd love it if the focus motor didn't sound like a dentist's drill every time it can't lock on target.

04-21-2008, 05:13 AM   #2
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the issue with using the latest ultra sonic motors is that they are distributed around the lens, and make use of the fact that the lens diameter is a few inches.

this is not practical in body
04-21-2008, 05:16 AM   #3
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So you're saying that making 3 or 4 mini-sdm motors turn a shaft inside the body is not actually doable? Damn...
04-21-2008, 05:36 AM   #4
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QuoteOriginally posted by ftpaddict Quote
I don't know to what extent this is possible, but couldn't Pentax use ultrasonic motors instead of the classic type, for in-body AF?

The aim would be to reduce AF noise most of all. I don't much care about AF speed, but I'd love it if the focus motor didn't sound like a dentist's drill every time it can't lock on target.
That's an interesting question. I've been more interested in *why* particularly the in-body drive is so noisy.

I've assumed it's not the motor that's noisy at all, but more likely the screw -- as the screw turn ratio to lens movement is very large. One turn of that screw barely moves the lens at all -- and I assume this is for the sake of accuracy, but if you have to turn the screw 1000 times to move the lens 1", it's going to be noisy no matter how silent the motor driving it is. . or likely, designing such a screw to have a high turn ratio and silent would be prohibitively expensive.

Then again, I'm taking wild guesses, so I have no idea.

Here's a link about Ultra-Sonic motors tho:

USM at the JPL's NDEAA

They are certainly a different kind of animal -- and from the looks of how they work, they look to be unsuitable to drive a high turn ratio screw. Their design suggests very small moments with a high degree of accuracy, very quickly -- the turn ratio is more like 1:1, a much different design from the in-body motor's very high turn to movement ratio.

Hell if I know tho. But I'm certainly curious.

If I was to design an in-body focus motor, I'd have to wait until we have a large SLR sized sensor with a live preview and a super high resolution video view finder -- then I'd mount the sensor on a voice coil, and have the sensor move back and forth to focus -- silent and very fast. But that scraps the whole idea of an SLR, which some would consider heresy.


Last edited by konraDarnok; 04-21-2008 at 05:43 AM.
04-21-2008, 05:57 PM   #5
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I think the transmission of the energy from such a motor would "fry" the mechanical link between the camera and the lens. When you look at the screw drive, it doesn't take long to figure that given the size of the screw driver, it can't handle high power, high torque for extended use. The mechanic just isn't sturdy enough to take a more powerful, faster spinning motor or drive mechanism.
04-21-2008, 09:12 PM   #6
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QuoteOriginally posted by konraDarnok Quote
If I was to design an in-body focus motor, I'd have to wait until we have a large SLR sized sensor with a live preview and a super high resolution video view finder -- then I'd mount the sensor on a voice coil, and have the sensor move back and forth to focus -- silent and very fast. But that scraps the whole idea of an SLR, which some would consider heresy.
And Contax did just that with their AX model. It moved the focus plane in an SLR film camera to focus. The ultimate in old lens compatibility. It reviewed fairly well, but it was not enough to save the business.
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