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11-04-2010, 08:52 AM   #1
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The Problem With Da* zoom "weather-sealing"

Hey While playing with my Da* in the rain i noticed a fatal flaw in the design, sent an e-mail to pentax about two weeks ago and did not get a response.

here's the problem

The DA* zoom lenses extend when they are zommed in and out

for a camera to properly weathersealed it must be "air tight" and when you "zoom" a lens out, you are creating a low pressure zone in the camera, which will then suck in water from the outside of the seals. i noticed that the weakest seal is by the eyecup for my k20d, and to my horror when i retracted the lens bubbles would show up coming out of the joint. now when i look for weather sealing i'd expect that it is sealed. now i am very cautious about going from 16mm to 50 mm on my lens in rainy conditions because it will suck in water from the outside of the camera. a scary thought when dealing with expensive equipment in the rain/snow, which is why i bought the product. thankfully my camera has had no trouble to date but i feel that this problem will be an issue as the camera ages and the seals get worn from "burping air in and out.

my suggestion:
create a series of internally zooming lenses for pentax,
as for me i think i will be moving over to primes, if anyone has a 50mm 1.4 da* and a bit of change, and wants a da*16-50 let me know, i am interested

11-04-2010, 08:58 AM   #2
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"Air tight? No. You want equal air pressure to account for differences in temperature. Moisture is primarily caused by the thermal break difference on one side of a material vs. another. In order to avoid moisture, you want to balance both the temperature difference and air pressure difference (because water moves due to energy). The real issue for WR is the ability to get moisture out if it is sucked in through mechanical means through baffles that drain/deflect or other means.
11-04-2010, 09:13 AM   #3
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hmm... so maybe an intermediate chamber, without sensitive electronics that would allow for the pressure to be equalized, and then the water that may be sucked in, to be drained out. i think that's what you are saying and it is a very interesting concept... is that in play in the pentax cameras?
11-04-2010, 03:58 PM   #4
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The da* 50-135 doesn't extend when zooming or focusing.

11-05-2010, 07:13 AM   #5
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sweet, maybe that is the next step, i was looking at the 60-250 but that deffinetly extends
11-05-2010, 09:20 AM   #6
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this issue is not new, and was pointed out several years ago, and even I think in some magazines.

For me, I like th eidea or a weather sealed camera, but I think lenses should be able to breethe a little
11-05-2010, 10:04 AM   #7
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I think that in the absence of anything other than some half baked speculation from someone who has yet to provide any sort of expert credentials on the subject of lens design, we can safely ignore this "concern" in the same way that Pentax seems to be ignoring it.
11-05-2010, 12:10 PM   #8
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plus 1

QuoteOriginally posted by Wheatfield Quote
I think that in the absence of anything other than some half baked speculation from someone who has yet to provide any sort of expert credentials on the subject of lens design, we can safely ignore this "concern" in the same way that Pentax seems to be ignoring it.
What he said, plus 1

11-05-2010, 12:42 PM   #9
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"Air tight" and "weather resistant" are vastly different tolerances.
11-05-2010, 12:50 PM   #10
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There does need to be an understanding of WR and its limits.
Sleet, gentle rain, snow, wind, dust resistant - quite different from air tight, water tight, water proof...
11-06-2010, 11:56 PM   #11
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i agree that the weather sealing has it's limits but when i look at what cannon is doing with it's l design glass, i think pentax should try and keep the lenses from expanding if they are weather-sealed, that way they won't suck in moisture when you extend the lens. i am by no means a lens design expert, but i don't want my camera to suck in moisture when i am out on a shoot.
I ice climb and sometimes when i am taking pictures of people on the ice on a nice sunny day, the ice will start to melt and i am in the middle of a waterfall, i still want to get the shot, that's why i bought the a camera from the brand with adds showing it getting doused by a martini.
i will be getting a camera with video soon, i'll link the movie here to show what is going on.
11-07-2010, 01:01 AM   #12
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I think Pentax has done reasonably well all this time without your advice, considering the huge issue you have uncovered. Now that they have been alerted to this important issue, future cameras will even be better.

We are all heavily indebted to you for having acted so promptly and decisively. I am glad my K20D is still working but I do think I will leave it at home from now on, so it runs none of the risk you detected.
11-07-2010, 01:49 AM   #13
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I think you would have to submerge the lens in water for it to suck in water before air.
11-07-2010, 05:47 AM   #14
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You are safe within reason. I have shot with my 16-50 in very wet conditions and never experienced any difficulty. I do (sort of) wish that Pentax had made it an internal zoom lens. However, then it would be extended fully all the time and would take up too much space in my bag. That is the trade off. The DA *60-250 is significantly shorter when retracted than most 70-200 lenses, because they are internal zooming designs.
11-07-2010, 07:33 AM   #15
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QuoteOriginally posted by Andrew Lang Quote
i agree that the weather sealing has it's limits but when i look at what cannon is doing with it's l design glass, i think pentax should try and keep the lenses from expanding if they are weather-sealed, that way they won't suck in moisture when you extend the lens. i am by no means a lens design expert, but i don't want my camera to suck in moisture when i am out on a shoot.
I ice climb and sometimes when i am taking pictures of people on the ice on a nice sunny day, the ice will start to melt and i am in the middle of a waterfall, i still want to get the shot, that's why i bought the a camera from the brand with adds showing it getting doused by a martini.
i will be getting a camera with video soon, i'll link the movie here to show what is going on.
There are plenty of sealed Canon "L" lenses that don't have internal zoom.
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