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04-13-2014, 09:23 AM   #1
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50-135 -- SDM or Screw -- what's faster?

I'm finally getting my dropped 50-135 repaired. CRIS quoted me $223 for the repairs, and there's a note:

**NOTE** THIS LENS HAS BEEN MODIFIED FOR SCREW-DRIVE AUTOFOCUS OPERATION TO RESTORE SDM AUTOFOCUS OPERATION AN ADDITIONAL $112.00 MUST BE APPROVED TO REPLACE THE SDM AUTOFOCUS MOTOR AND MAIN PCB

The lens was already modified for screw drive when I got it. The sound of the screw drive doesn't really bother me, especially now that I have the 60-250 which I'd probably be using in a venue where tiny sounds would be annoying to someone. But I wouldn't be opposed to getting the SDM fixed.

My question is this: On a K5, does the screw drive modification produce faster AF than the SDM motor? And on a K3, with the upgraded screw drive motor, which one is faster?

Thanks!!!

04-13-2014, 10:42 AM   #2
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Screw-drive is faster than SDM on the 50-135. I have used it on an SF1, ZX-50, K-50, and K-3.
If you don't require SDM and CRIS will repair it for screw-drive only, go for it.
While I wouldn't deliberately disable SDM, the redundant screw-drive system makes SDM failure a "champagne problem" IMHO.
04-13-2014, 11:15 AM   #3
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Let me break this down:

1. You bought a used DA50-135 converted to screwdrive autofocus.
2. You dropped the lens and send it in for repair
3. CRIS repairs your lens, and also offers to replace SDM motor and circuit for additional U$112

So, can you afford the extra expense? Also have in mind that the replacement probably is the newer version of the motor which shouldnt break as the old one. And the lens will be silent when focusing.
Regarding speed, Ive read theres no difference between sdm and screwdrive several times. But screwdrive could be faster on the K-3 because it has a stronger motor than K-5 series. Not confirmed though.
04-13-2014, 12:01 PM - 1 Like   #4
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I can afford it or I wouldn't have asked.

I'd rather have faster AF than quieter AF. I'm going to upgrade from my k5 to a k3 eventually. I was very happy with the 50-135 as it was. So, if all it's going to get me is slower quieter autofocus, I can just take the $112 and put it in my k3 fund.

04-13-2014, 12:05 PM   #5
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QuoteOriginally posted by narual Quote
I'd rather have faster AF than quieter AF. I'm going to upgrade from my k5 to a k3 eventually. I was very happy with the 50-135 as it was. So, if all it's going to get me is slower quieter autofocus, I can just take the $112 and put it in my k3 fund.
Whether or not it is any faster, (I've no idea) also consider the resale value. A completely repaired lens with the option of SDM or screwdrive would surely be worth more than one converted to screwdrive and a failed SDM. Will CRIS repair the SDM and leave it converted to screwdrive? For $112 extra you have a completely repaired and functional lens. I would not hesitate to pay the extra but that's just my opinion.
04-13-2014, 03:04 PM   #6
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QuoteOriginally posted by jatrax Quote
Whether or not it is any faster, (I've no idea) also consider the resale value. A completely repaired lens with the option of SDM or screwdrive would surely be worth more than one converted to screwdrive and a failed SDM. Will CRIS repair the SDM and leave it converted to screwdrive? For $112 extra you have a completely repaired and functional lens. I would not hesitate to pay the extra but that's just my opinion.
But will a repaired SDM get an extra $112 dollars in resale VS just selling the 50-135 as is with the screwdrive? I'm not so sure.

I would just enjoy the reliable and fast screwdrive.
04-13-2014, 07:58 PM   #7
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QuoteOriginally posted by EarlVonTapia Quote
But will a repaired SDM get an extra $112 dollars in resale VS just selling the 50-135 as is with the screwdrive? I'm not so sure.
I don't know either, just something to think about.
04-13-2014, 11:16 PM   #8
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I have the k3 and the 50-135, I enjoy the silence SDM, but I think the screw mount is faster. But don't quote me on that...

04-14-2014, 07:03 AM   #9
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If only I had an older camera body that I could use to convert it. But I don't think the k5 can, if I read right.

---------- Post added 04-14-14 at 10:52 AM ----------

Hmmm apparently I didn't look hard enough and they found a way to get the K5 to do it. Maybe I'll get it fixed, since I can switch it back to screw drive later. Of course, I'll have to dig out an old windows PC (or borrow a friend's) to do it.

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/208353-how-...ml#post2737443
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