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07-18-2010, 02:43 AM   #1
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A guess why DA*'s have various issues, Nikon's possible reason.

I was fishing around a few other forums. I'm always on the hunt for new wedding info and ideas and of course the bulk of the shooters are either Nikon or Canon. So you pick up other threads on their systems while looking around.

I stumbled upon a discussion about weather sealed lenses. Nikon does not make any. Period. The 24-70mm F2.8 sells for $1600 or so and is dust protected but NOT water sealed. Same for the even more expensive 70-200mm f2.8. This comes straight from Nikon. Nowhere in their literature does it say, go play in the rain. This is true for the entire lens line. Many of their lenses have a dust "O" ring on the back but they don't build them to resist water.

So I'm tossing out a theory here and it's a pure guess. These guys do a lot of R&D for the Pro market. Did they discover that by making the lens WR to resist water, that it put too much strain on the lens drive motor? Sealing the lens against water caused too much friction in moving barrel parts. It made the lens slow to focus and burned out motors.

The only thing that somewhat shoots this down is, lenses like the DA*16-50mm are internal focus. So the moving parts are inside the lens. But the barrel does extend to zoom. So the outside does move. Also the zoom action seems to be smooth and nearly friction free. Mine have all been very easy to zoom in and out. Of course the zoom action doesn't have anything to do with the motor directly

I know I'm guessing here but could this be the reason we've seen problems with DA* zoom motors and lenses like the DA*55mm reported as very slow to focus? I really don't know he answer but it seems very strange that Nikon doesn't offer this on at least a few lenses. Considering the cost is so much on some of them, they would offer this feature on at least a few of them but they don't. Is this Pentax advantage, really not an advantage at all?

07-18-2010, 03:31 AM   #2
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Neither 16-50 nor 50-135 are WR, and these are like the worst lenses when talking 'bout sdm issues. DA55 is also not WR. But your theory is interesting nontheless. Thnx for the input
07-18-2010, 03:37 AM   #3
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Excuse me? Straight off the Pentax web site (USA):

The PENTAX *DA series of high grade lenses, designed exclusively for PENTAX digital SLR cameras, features the quiet SDM focus system and tightly sealed, weather-resistant and dust-resistant construction to enhance durability for use in rainy or dusty conditions.

Then for the product directly:

-The tightly sealed, weather-resistant and dust-resistant construction enhances durability for use in both rainy and dusty conditions, making the DA Star 16-50mm lens a perfect companion for the weather-resistant PENTAX DSLR bodies.
07-18-2010, 03:41 AM   #4
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QuoteOriginally posted by 1marek Quote
Neither 16-50 nor 50-135 are WR, and these are like the worst lenses when talking 'bout sdm issues. DA55 is also not WR. But your theory is interesting nontheless. Thnx for the input
Silly, silly. All of the DA * lenses are weather resistant. This includes the 60-250, 50-135, 55, 200, 300 and 16-50.

I have a hard time believing the theory though. My feeling is that Pentax, in order to make the DA * lenses as small as possible used under powered motors. Sort of like putting an inadequate transmission in a powerful car. It just burns out over time. The problem is that due to space constraints, they are limited as to what motors they use.

07-18-2010, 04:17 AM   #5
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Rondec, that may be true. but it doesn't explain the slow focusing. I have a K20D that has the SDM disabled in the body. The motor in the body works as it should. So my DA*16-50mm on that body works as a screw drive lens. If I put it on the other 3 SDM cameras I have, the focus is fine in daylight but slow indoors or tougher lighting. On the K20D in screwdrive only it's just the same, Slow in low light and you need to do little tricks to get it to lock on.

It's a fast lens, so that shouldn't be the issue. It can gather lots of light and it produces very good contrast. So I'm assuming it's not the optical formula. Same for the DA*55mm which at f1.4 should gather as much light as any lens available.
07-18-2010, 05:41 AM   #6
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QuoteOriginally posted by Peter Zack Quote
Rondec, that may be true. but it doesn't explain the slow focusing. I have a K20D that has the SDM disabled in the body. The motor in the body works as it should. So my DA*16-50mm on that body works as a screw drive lens. If I put it on the other 3 SDM cameras I have, the focus is fine in daylight but slow indoors or tougher lighting. On the K20D in screwdrive only it's just the same, Slow in low light and you need to do little tricks to get it to lock on.

It's a fast lens, so that shouldn't be the issue. It can gather lots of light and it produces very good contrast. So I'm assuming it's not the optical formula. Same for the DA*55mm which at f1.4 should gather as much light as any lens available.
Your theory is supported a bit by the impression I have that the DA17-70 seems to have fewer SDM problems, and the issues that people report seem to be different. The focus on my DA17-70 is also as fast as any screw drive lens I own, and faster than most.
07-18-2010, 05:48 AM   #7
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I never thought about that Gene. You may be on to something. We've seen a couple SDM issues with the 17-70 but nothing like the 16-50mm. Plus the lens you have is f4 so in theory, it shouldn't be faster than an f2.8 or f1.4 lens.
07-18-2010, 06:01 AM   #8
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QuoteOriginally posted by Peter Zack Quote
I never thought about that Gene. You may be on to something. We've seen a couple SDM issues with the 17-70 but nothing like the 16-50mm. Plus the lens you have is f4 so in theory, it shouldn't be faster than an f2.8 or f1.4 lens.
The fastest AF lens I own is F1.8. On reflection, I would have to say the AF speed champion in my bag actually is the much-lighter and "faster" FA35/2 with the DA17-70 right behind it.

07-18-2010, 06:37 AM   #9
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You're forgetting the other brand, Canon, and some of their L lenses. How come they can make lenses that are dust and weather resistant (but not water sealed), and still have USM focusing that's fast and quiet, and doesn't self destruct like SDM seems to do...
07-18-2010, 07:17 AM   #10
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QuoteOriginally posted by pop4 Quote
You're forgetting the other brand, Canon, and some of their L lenses. How come they can make lenses that are dust and weather resistant (but not water sealed), and still have USM focusing that's fast and quiet, and doesn't self destruct like SDM seems to do...
I was just going to mention that owning L glass I know they are WR. The thing is though... unlike Pentax Canon does not offer WR on all of their L line.

For example the 17-40L is WR ONLY if you add a filter to the front of it (odd design, but the barrel of the camera is static, and the end element floats and moves inside that barrel). Otherwise its just dust sealed.

The reality is its hard to compare against the Canon, but they all use USM and offer dust resistance. They don't seem to have an issue.

From what I have read about how Pentax seals the glass... is that it uses felt/cloth O-Rings inside the barrels and focusing points (basically all the parts that need to move/rotate within eachother)... and the actual elements are sealed off completely from water/moisture, which I am guessing involves rubber seals and cementing. The cloth O-Rings don't cause enough friction for me to believe its wearing down the SDMs.... however maybe the SDMs are just so weak that any additional friction does cause it to fail early. The Canon's and Nikon lenses use a very similar type of dust sealing as well.

Of course I could be completely wrong.

Last edited by kalison; 07-18-2010 at 07:23 AM.
07-18-2010, 08:14 AM   #11
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I wasn't forgetting Canon, just not sure of the facts and also they use a different motor system correct? Ring motors that are even stronger. But as posted above, maybe the Pentax motors were a compromise over size/strength and that's a large isse.
07-18-2010, 08:41 AM   #12
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From what I've seen their ring motors are a good size. They are the nice FTM ones.

Canon also uses micro usm, but uses those primarily in the lesser expensive glass, such as the EF-S glass. L glass -in general- use the higher end ring usm.

From what I have heard the micro usm motors from canon are not the most reliable either, they have a poorer track record. Maybe not like Pentax, but it's worth noting even Canon has issues with small usm.


Edit: wanted to add not just EF-S (even some of those higher end ones use ring) uses micro usm, but in general many of Canon affordable lenses use the micro usm, don't forget they also use their cheapest motor which is a standard micro dc motor, which are louder.

Last edited by kalison; 07-18-2010 at 08:54 AM.
07-18-2010, 10:13 AM   #13
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one thing for sure, is that Pentax used a very fragile motor that has a small stress tolerance and could wear out easily.

if I were to make an analogy, it would be more or less like the XBOX 360 3 ring of death phenomena. the culprit behind that was due to the fact that they installed a substandard cooling system in maintaining a heat-prone gpu. such stress could cause the weak cooling system to break down at such a short period of time.
07-18-2010, 11:48 AM   #14
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The Canikon answer.

07-18-2010, 01:56 PM   #15
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QuoteOriginally posted by SpecialK Quote
The Canikon answer.

(Unfortunately no "Pentax Answer" shot is available. The photographer's lens was in for repair.)
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