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04-11-2012, 02:43 AM   #16
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QuoteOriginally posted by Mike.P Quote
Sorry Stefan .. changed it just before your post.

I have changed the post as I wasn't being particularly clear. There have been no SDM lenses released since before the 18-135mm, the last being the 55mm.
Well there aren't any new DA* released so it does not prove or disprove anything at this point.
there is a DA* on the roadmap, just need to wait and see, that's all we can do for now.

04-11-2012, 02:48 AM   #17
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QuoteOriginally posted by axl Quote
I thought that would be matter of gearing rather than power of the motor itself...
QuoteOriginally posted by Mike.P Quote
My point is that you get both with the Sigma lenses.
Yeah and also lens design of course.
The 18-135 use the rear group to focus and that's a very fast method and i don't believe the focus throw is great on this lens.
If we take the DA*50-135 you will notice the how much you can turn the focus ring don't know how that one compares with the Sigma though.

What i'm saying is that's hard to compare this thing because there are so many variables and differences in design phylosophies, and the HSM and SDM are the same type of motor so that's not part of the differences between Sigma and Pentax.
Does tokina maybe have a clone with build in motor that are comparable?
04-11-2012, 03:13 AM   #18
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QuoteOriginally posted by Anvh Quote
Yeah and also lens design of course.
The 18-135 use the rear group to focus and that's a very fast method and i don't believe the focus throw is great on this lens.
If we take the DA*50-135 you will notice the how much you can turn the focus ring don't know how that one compares with the Sigma though.

What i'm saying is that's hard to compare this thing because there are so many variables and differences in design phylosophies, and the HSM and SDM are the same type of motor so that's not part of the differences between Sigma and Pentax.
Does tokina maybe have a clone with build in motor that are comparable?
not with sonic type motor AFAIK.

all their lenses codevelped with Pentax use conventional motor in lens...
04-11-2012, 04:50 AM   #19
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QuoteOriginally posted by Anvh Quote
HSM is the same type of motor as SDM so what's your point?
Some HSM lenses use different (better) ring motors.
Some use micro motors similar to SDM.

None have a shoddy history like SDM.

04-11-2012, 04:54 AM   #20
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But why not just use bigger, more powerfull DC motors for the lenses with the bigger elements then?
04-11-2012, 05:37 AM   #21
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QuoteOriginally posted by axl Quote
not with sonic type motor AFAIK.

all their lenses codevelped with Pentax use conventional motor in lens...
too bad

QuoteOriginally posted by Class A Quote
Some HSM lenses use different (better) ring motors.
Some use micro motors similar to SDM.

None have a shoddy history like SDM.
Only the DA*16-50, DA*50-135 and 17-70 have big problems with the AF, i'm still not sure what's going on there. if they use different SMD or if it's AF mechanism.

From what i read the 17-50 use a geared HSM not a ring-type not sure about other lenses.

QuoteOriginally posted by Clavius Quote
But why not just use bigger, more powerfull DC motors for the lenses with the bigger elements then?
More powerful motor means more power which comes with their own limitations with the electronics and the battery, they could use DC with different gearing but means lower speed.
Besides why would you want DC when SDM seems to be working really well with the more recent DA* lenses. DA*60-250, DA*55, DA*200, DA*300 all are so good as problem free.
Pentax should never have used the KAF2 mount, i think that's where most of the problems lies with the dual (triple if we count manual) focusing mechanism
04-11-2012, 05:48 AM   #22
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I've only had my 50-135 for two weeks, but i don't understand what you guys mean with inconsistent and inaccurate AF? I find it very consistent and accurate, and it's faster than my 18-55 and 50-200.
04-11-2012, 05:51 AM   #23
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funny, the survey seems to suggest all the SDM zooms have problem including the 60 250?

04-11-2012, 06:09 AM   #24
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QuoteOriginally posted by morpho Quote
I've only had my 50-135 for two weeks, but i don't understand what you guys mean with inconsistent and inaccurate AF?
They are talking about the DA*16-50 with his inconsistent focus but that lens has his share in terms of quality control and what not...
Quite a few have found that lens elements are decentered and such so if we can blame SDM for that?

Problem is that SDM has build up such a name that every little problem concerning focusing is blamed on it while it can easily be something else.

Last edited by Anvh; 04-11-2012 at 06:31 AM.
04-11-2012, 06:20 AM   #25
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QuoteOriginally posted by lightbulb Quote
funny, the survey seems to suggest all the SDM zooms have problem including the 60 250?
yeah but 5 out off 105 is not a bad score at all that's 4,75% that failed and the primes are even lower, that's really not bad.
Just look at this chart for comparison, different situation though but still.
LensRentals.com - Lens Repair Data 2011

list from previous years.
http://www.lensrentals.com/blog/2010/09/lens-repair-data-4-0
04-11-2012, 06:49 AM   #26
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True too, I am sure there were more than 105 copies sold, so the failure rate should be lower. But the zero failure of 18-135 is even more impressive consider the number of 18-135 sold.

The fact is DC motor is 100% reliable, reasonably priced and in most cases AF faster than SDM. I think the K5 image is about big bang for buck, good quality, tough and reliable, and DC fits that image better than SDM. I have zero knowledge about lens motor so I don't know the DC limitation on big zoom lenses, but if it can be used on most zooms and primes I think there will be more happy Pentaxians and converts I would think?
04-11-2012, 06:56 AM   #27
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QuoteOriginally posted by lightbulb Quote
I don't understand why Pentax is so fixed on using SDM despite all the cons.
My guess is that the DC motor is something designed and used by Tokina, and Pentax is not involved in "choosing" to use it. See this thread here.

So the Pentax answer of "DC for budget lenses" means that Tokina is moving away from screwdrive in all of its mass-market (later rebranded for Sony, Pentax, Nikon, etc.) lenses - probably because a major rebranding customer (Nikon) no longer puts screwdrive motors into its low-end bodies. It's possible that when the (re-hired?) lens designers at Pentax design a new lens, they have a choice to use SDM and/or screwdrive, and only if they contract Tokina to build it would they get the option of DC. Tokina would then get the optical design for their own sales, which might not be worth it for Pentax.
  • But why does Pentax stick with SDM, and not come out with SDM2? No idea, but until new Ricoh-era lenses actually come out, we won't know if they have stuck with it!
  • Why not license the DC motor from Tokina? Again, who knows what the agreements would involve, or if it's worth it (maybe it only works on light zooms).
  • Why is Sigma's HSM so much better than SDM? Sigma (apparently) doesn't license designs or tech from, or to, anybody else, so they either get it right or lose sales to Nikon SWM and Canon USM-equipped OEM lenses. Do they care about Pentax SDM? Sigma can barely justify mass-producing the K-mounts, it sometimes seems.

Last edited by panoguy; 04-11-2012 at 07:14 AM.
04-11-2012, 07:11 AM   #28
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SDM lenses are definitely better than DC lenses. It says so right in the price list.
04-11-2012, 07:16 AM   #29
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QuoteOriginally posted by lightbulb Quote
The fact is DC motor is 100% reliable
Problem with saying this is there is only one DC lens and we see with SDM failures how some lenses are really effected and others not.

If we didn't had the DA*16-50, DA*50-135 and DA17-70 we would have another over all view on SDM as well.
04-11-2012, 07:23 AM   #30
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Thanks for the explanation. I am actually eyeing on 5D III and waiting for reliable reviews to pull the trigger. If there isn't much reason to stay with Pentax I would go into Canon system. I find Pentax a bit lack in tackling their problem and communicating with its supporters, not good. But I respect their culture and wish them well.
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