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05-09-2011, 10:38 AM   #16
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QuoteOriginally posted by hjb981 Quote
What happens with the air in a weather sealed camera + lens system when the lens is being zoomed? Air has to go in and out of the camera then, or a pressure difference would be created. Does anyone know how this happens? Perhaps there is a little vent hole, with a filter in it, or does air just slip by the seals?
At last!!!! It's nice to see that some common sense is starting to reach Pentax community... There's hope after all!!!

05-10-2011, 02:06 PM   #17
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That was very interesting - I did not know that there HAD been issues with compacts (Canon G9 was mentioned) - I used them as an example of completely dust-proof systems when it came to the sensors, assuming that they were. I have experienced lots of dust on the inside of the screen on my old Konica Revio KD-510Z, but nothing on the sensor.

This is a little bit off topic, but the idea of taking apart a lens made me think of these videos:
Taking apart a camera and analyzing what does what:
Ny Teknik sätter mejseln i systemkameran - NyTeknik
Putting it back together:
Så fick Under Skalet ihop kameran - NyTeknik
Taking apart a lens:
Under skalet synar objektivet - NyTeknik

The camera and lens is a Canon 500D and the kit 18-55 that it comes with. NyTeknik is a Swedish magazine (with on-line videos), so all of the analyzing while taking the things apart is in Swedish. D-SLR:s are rather complicated!

Anyways, whether the air goes by the seals or through some filtered vent hole, I do like having a camera that lets as little water and dust in as possible. And if the air does go by the seals, that does not have to mean that water could take the same route. Water is much more viscous than air.
05-10-2011, 03:12 PM   #18
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I may be able to shed some light on the air in/out issue. I recently purchased a K5 with the 18-135 WR that literally made a slight whistle sound when zooming. This did not happen all the time. Thinking it was the lens making the sound I called Pentax to get their take on it and they said send it in or get a replacement from the dealer. I got a replacement and mounted the new lens only to find the sound still occurred but now more often. In trying to isolate where on the lens the sound was coming from I held it close to my ear and tried zooming it in and out. While doing this I noticed that I could feel a slight puff of air on my face coming from not the lens but the shutter release button. I could also hear the whistle sound coming from that location more clearly. To test my observation I put a small piece of lens tissue over the shutter release button and carefully zoomed the lens in. When I did this the tissue lifted off the button. I repeated this a few times and it happened every time. My theory was that shutter release button was the area that the air was designed to travel in and out of the camera. If some kind of valve or filter is involved that was most likely making the noise I was hearing. I called Pentax to tell them what I was observing and again the advice was to send it in or get a replacement, this time for the camera body. Whether it's designed this way or I was seeing a flaw I have no idea. The noise was a nuisance. Love the camera though.
05-11-2011, 02:21 PM   #19
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JED - I have no hissing sound on mine, and I tried with a piece of lightweight magazine paper as well as holding the shutter button too my cheek when zooming without any indication of air from the shutter button. Either something is wrong with the seal around your shutter button, or maybe you just zoom faster than I do . I do not zoom very fast, because I am always careful with anything mechanical. This time, I zoomed as fast as I dared (meaning so that it does not feel like forcing the lens, about 1.5 seconds all the way on the 18-135 WR). Anyways, it is not likely that it is designed to vent there, in my opinion. Such a hole should be pointing downwards if it exists, to minimize the risk of rain getting in.

05-11-2011, 02:43 PM   #20
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The camera doesn't have to vent. Zooming will only create a partial vacuum or pressure, so all it means is that there is extra resistance to movement and more motor power would be needed than if it were to vent (quickly). It's just as if there were a spring added.
05-11-2011, 04:30 PM   #21
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QuoteOriginally posted by SteveB Quote
The camera doesn't have to vent. Zooming will only create a partial vacuum or pressure, so all it means is that there is extra resistance to movement and more motor power would be needed than if it were to vent (quickly). It's just as if there were a spring added.
Simple math demonstrates why this theory is impossible. Atmospheric pressure is a tremendous force. Take the 18-135 for example, which doubles in length zoomed out. If it were airtight, that would indicate roughly a half atmosphere of pressure differential. Let's do some rough calculations to see the force exerted on the front element:

Atmospheric pressure: 101,325 pascals
Front element filter diameter: 62mm (0.062m)
Area of front element: pi*(0.031m)^2

Force on front element = (101325/2)*pi*(0.031m)^2 = 160 newtons = a whopping 15.6 kg/34.3 lbs

I hardly think you exert that much force to zoom the lens. And that's just on the front element. The total force on the barrel itself (much larger surface area) would be in excess of 150kg/330lbs. The plastic barrel would never hold up. The thing would implode, violently.

Last edited by Cannikin; 05-11-2011 at 07:03 PM.
05-12-2011, 04:28 AM   #22
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I started a thread some weeks ago to do with this topic and a fiery discussion ensued as a consequence. You may look here:

https://www.pentaxforums.com/forums/pentax-k-5-forum/138678-venting-zoom-lenses.html

another related thread here:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/124169-moisture-lens-barrel.html

Greetings
05-12-2011, 05:14 AM   #23
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QuoteOriginally posted by Cannikin Quote
Simple math demonstrates why this theory is impossible. Atmospheric pressure is a tremendous force. Take the 18-135 for example, which doubles in length zoomed out. If it were airtight, that would indicate roughly a half atmosphere of pressure differential. Let's do some rough calculations to see the force exerted on the front element:

Atmospheric pressure: 101,325 pascals
Front element filter diameter: 62mm (0.062m)
Area of front element: pi*(0.031m)^2

Force on front element = (101325/2)*pi*(0.031m)^2 = 160 newtons = a whopping 15.6 kg/34.3 lbs

I hardly think you exert that much force to zoom the lens. And that's just on the front element. The total force on the barrel itself (much larger surface area) would be in excess of 150kg/330lbs. The plastic barrel would never hold up. The thing would implode, violently.
Just a thought...



When attaching a zoom lens the air pressure is fairly static. Now when zoom ing the air pressure becomes negative in the lens and body. The bodies are fairly air tight. How much pressure would there be on the total area of the seals on the outside trying to get in? Moreover how much water/dust would ingress/egress with the air? In other words how big would the opening be to allow water or dust in/out?

OK say very little or no air gets back in the lens. If you zoom back in the pressure is just back to normal; no increase of air pressure relative to its state when putting the lens on.



Now what if you put the lens on with the zoom at max like 250mm on the DA*60-250mm then zoom back down. Well there would (I don't know the math) be logically a large increase of internal air pressure wanting to get out. Again because the bodies are the tightest of the two the air would probably go past the oring seals in the lens and blow out and not let anything in. Then the lens/body seals could handle the slight negative pressure of being zoomed out? Perhaps?

Its fairly certain (we have service manuals) that there is no vents on the bodies. No vents appear on any sealed lens I have handled. Where does the air go?

I will admit I am no physics math guy. But IMO there is a small pressure differential on both sides of the lens seals (when zoomed out/in) that will let air slowly ingress and quickly egress. Another thought is the DA* lens and WR bodies are also dust tight and that's really hard to do.


Last edited by jamesm007; 05-12-2011 at 05:31 AM.
05-28-2011, 12:23 PM   #24
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QuoteOriginally posted by soppy Quote
Easy way to check would be to take a DA* 50-135 and submerge it, it if bubbles, then its not airtight, though that'd be a colossal waste of a great lens as my money is on it bubbling...
I'd LOVE to see this...
05-28-2011, 12:34 PM   #25
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i make it a habit to tape over all the buttons on my cams with basic black electrical tape, to hide the distracting icons and logos and end up with just a black block. Did that with my K-7 too after a few months, once i knew where and what all the buttons were.

Electrical tape being not especially sticky or conformant, it just sits on top of the circle of buttons in the back. When i zoom a lens in and out i can see the tape there puff in and out, so conclude there's an air vent in with those buttons. i've since made sure the tape there either has holes in it or other open air passages.

If the K-5 has the same body then i'd assume it'd have equivalent venting.

Last edited by conradj; 05-28-2011 at 12:42 PM.
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