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09-01-2012, 07:11 AM   #1
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Ring motor patent

I hope this motor design will find it's way into some new Pentax lenses:

Patent US20110007408 - TORIC MOTOR AND LENS BARREL HAVING THE SAME INCORPORATED THEREIN - Google Patents

Looks like a more detailed embodiment than previous applications:

Patent US20090323208 - ROTARY ACTUATOR - Google Patents

Certainly won't find it in budget lenses though as it looks difficult to make.

09-01-2012, 07:46 AM   #2
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I think this AF drive system, or a variant of it, is in the 18-135 zoom.

The price of the 18-135 might not be low enough to qualify as a budget lens, but given the variable 3.5-5.6 aperture, it is clearly a consumer-oriented zoom.

Reading reviews of the 18-135, it seems that the 18-135 AF is quiet, smooth and accurate, but not fast like other ring motor implementations from other brands, and according to Photozone, not even as fast as normal SDM, which I find to be quite slow.

I have not used this lens, however, as for various reasons, I long ago swore off variable aperture consumer zooms, so maybe someone with direct 18-135 experience will chime in.

Ray
09-01-2012, 07:58 AM   #3
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I'm not entirely sure, but I have only heard reports of fast focusing with the 18-135..
09-01-2012, 08:24 AM   #4
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QuoteOriginally posted by JinDesu Quote
I'm not entirely sure, but I have only heard reports of fast focusing with the 18-135..
Yeah, everything I've ever read says that it's pretty fast.

09-01-2012, 08:39 AM   #5
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quite old news
09-01-2012, 08:40 AM - 1 Like   #6
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Definitely not. The 18-135mm uses a simple, small DC motor coupled to a plastic gear train. You can see it when looking through the back of the lens when it is fully zoomed out. It is a cheap and simple implementation. Also, when manually focusing you are actually back-driving the gears and motor.

The reason its faster and more accurate is probably due to much less backlash in the drive system (fewer gears) compared to a body system.

The motor in the patent application would provide much higher torque and could probably be a direct drive without any gear reduction however would be significantly more expensive due to it's complexity.

QuoteOriginally posted by Ray Pulley Quote
I think this AF drive system, or a variant of it, is in the 18-135 zoom.

The price of the 18-135 might not be low enough to qualify as a budget lens, but given the variable 3.5-5.6 aperture, it is clearly a consumer-oriented zoom.

Reading reviews of the 18-135, it seems that the 18-135 AF is quiet, smooth and accurate, but not fast like other ring motor implementations from other brands, and according to Photozone, not even as fast as normal SDM, which I find to be quite slow.

I have not used this lens, however, as for various reasons, I long ago swore off variable aperture consumer zooms, so maybe someone with direct 18-135 experience will chime in.

Ray
09-01-2012, 08:40 AM   #7
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QuoteOriginally posted by Ray Pulley Quote
I think this AF drive system, or a variant of it, is in the 18-135 zoom.
Nope the 18-135 uses a small DC motor, nothing special about it.
09-01-2012, 08:41 AM   #8
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QuoteOriginally posted by Ayoh Quote
The reason its faster and more accurate is probably due to much less backlash in the drive system (fewer gears) compared to a body system.
The DA18-135 uses special rear element to focus and such designs are aimed to be fast focusing.

09-01-2012, 11:04 AM   #9
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Indeed but it still doesn't explain why photozone finds it slow to ficus when every (or nearly) member here found it to be fast focussing
09-01-2012, 01:07 PM   #10
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QuoteOriginally posted by thibs Quote
Indeed but it still doesn't explain why photozone finds it slow to ficus when every (or nearly) member here found it to be fast focussing
Because Photozone are used to test Canon and Nikon lenses .
09-01-2012, 04:20 PM   #11
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QuoteOriginally posted by Ray Pulley Quote
Reading reviews of the 18-135, it seems that the 18-135 AF is quiet, smooth and accurate, but not fast like other ring motor implementations from other brands, and according to Photozone, not even as fast as normal SDM, which I find to be quite slow.
Their exact words are "The new DC AF motor may not be as fast as Pentax' SDM", which I would not necessarily interpret as them saying it actually is slower, just that it may be. Also, check this video, in which the DA 18-135 is compared to both the DA* 50-135 and the FA 50:
.
09-02-2012, 01:25 AM   #12
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But the FA50 and DA*50-135 have a huge focus throw compare to the DA18-135, compare the DA*16-50 with the later instead.
09-02-2012, 02:42 AM   #13
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Indeed. I'm not sure about the 18-135 but the FA50 and DA*50-135 have VERY long focus throw.
09-02-2012, 03:10 AM   #14
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QuoteOriginally posted by Anvh Quote
But the FA50 and DA*50-135 have a huge focus throw compare to the DA18-135, compare the DA*16-50 with the later instead.
Ok, but what point are you trying to make, given that the FA 50 seems faster and the DA* 50-135 seems slower than the DA 18-135?

edit: Btw, what I also find strange, is that when the DA* 50-135 at 135mm is focussing on the bear, it first focuses in the opposite direction, stops, and then goed into the correct direction, like the focusing system doesn't know which way to turn to until it is actually focusing. Yet this is phase-detect AF, so it should always know, right? Does anyone know why it does this?
09-02-2012, 04:42 AM   #15
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The motor has to move a greater distance with the DA*50-135 then with the DA18-135, so the motor might indeed turn (slightly) faster but because of the greater distance the focus mechanisms travels the lens focus slower.
You get it?

The DA*16-50 has a shorter focus throw so it focus faster, if the focus throw is comparable with the DA18-135 those might be a good comparison.

The shifting focus with the DA*50-135 might be because of the f/2.8 making the contrast less clear.
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