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05-14-2010, 06:42 AM   #1
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Hypersonic or screw AF???

You will have to excuse me but i do not know this answer.

What is the advantage other than noise to the Hypersonic AF to the screw drive?
I have the screw drive and am happy with it. It focuses spot on and very fast. A little noisy but other than that i can tell you it is perfect.

I want someone to explain what the advantages are? It seems to me like it is something else to go wrong to the internal workings to the lens.
Thanks in advance.

05-14-2010, 06:52 AM   #2
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Garyk: SDM is supposed to offer *speed* and be quiet. Many have said that the speed is not much if any faster than the screw drive lenses. I guess that is debatable. It is quieter. Sometimes so quiet it seems to not be working. Sorry, I couldn't resist. I have stuck with the screw drive until SDM reliability improves.
05-14-2010, 07:16 AM   #3
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QuoteOriginally posted by garyk Quote
You will have to excuse me but i do not know this answer.

What is the advantage other than noise to the Hypersonic AF to the screw drive?
I have the screw drive and am happy with it. It focuses spot on and very fast. A little noisy but other than that i can tell you it is perfect.

I want someone to explain what the advantages are? It seems to me like it is something else to go wrong to the internal workings to the lens.
Thanks in advance.
As far as I know, SDM is not reliable unfortunately. You can see tons of reported SDM failure on this forum. This is the only reason I kept myself distant from otherwise superb 50-135mm
05-14-2010, 07:17 AM   #4
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If implemented properly, HSM/USM/SDM/etc is supposed to be faster than screwdrive.

As I understand it, the SDM implementation in Pentax lenses isn't so hot. Sigma's HSM implementation in their lenses seems quite nice - I'm very happy with my 18-250 HSM OS.

05-14-2010, 07:34 AM   #5
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SDM is a lot slower than I thought it would be but as for reliability I have the 16-50mm, 55mm, 50-135mm, 200mm and 60-250mm and they have worked faultlessly.
05-14-2010, 07:38 AM   #6
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QuoteOriginally posted by Mike.P Quote
SDM is a lot slower than I thought it would be but as for reliability I have the 16-50mm, 55mm, 50-135mm, 200mm and 60-250mm and they have worked faultlessly.
good for you !
05-14-2010, 12:00 PM   #7
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If the motor is in the lens, it can be exactly the right motor for the lens. An in-body motor has to be a compromise. That could mean noise, speed, weight and accuracy improvements. The advantages are not really there yet in the Pentax lenses.
05-14-2010, 05:59 PM   #8
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Well the way i understand AF. It is an algorithem that is calculated by the camera body.
Whether it be a hypersonic motor or not. The calculations come from the camera.

With the k-20 and k-7 there is a variable that can be changed from a plus 10 to a minus ten that changes the focus point only. This being backward focus and forward focus. This means focus is aquried by the camera properly everytime but the forward focus and backward focus point can be adj. by you.

So the hypersonic drive gets instructions from the camera as well as the screw drive that drives the focus.

I can see where the internal focus on a SMC would be faster but not more acurate. If the signal from the algorithem is not satisfied with the focus, then it will microadjust until it is. By micro-adjust i mean tweeking the screw or SMC until it is satisfied.

The only way i can see where it makes a difference is after focus is aquired the screw has some slop in it and it moves a tiny bit from the point where focus is aquired, and the time you shoot the shot. By not holding tight the mechinism that holds the focus of the lens.

If i am correct then i will stay with the screw focus for now.

With in camera stabilization and screw focus the Pentax is poised to take over the market. Why it doesnt get its shit togeather is beyond me.

One more thought is why it doesn't let you set the lens you are using for the image stabilazation. If the lens sends the info to the camera, the function is not setable. If i use a lens that is reconizable and then add a 1.4 or 2.0 T.C. and enable the lens stabilation function. The stabilization algorithem that is set for the lens is wrong??????? I think this is the case.
Does anyone know how the camera sees the lens and sets the algorithem for the stabilization mode? I would be interested in knowing if the algorighem changes the way the stabilation performed for a ( 300mm lens with a 1.4 T.C. connected ) to produce stabilization.

Thanks in advance.

05-14-2010, 06:02 PM   #9
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i think i may actually prefer a camera that doesnt sound like a driller
05-14-2010, 07:05 PM   #10
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QuoteOriginally posted by tokyoso Quote
i think i may actually prefer a camera that doesnt sound like a driller
I was surprised that the AF is much more civilized in live view mode. I never use it, but it's very intuitive for your friends who don't know the camera.
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