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03-30-2011, 11:34 PM   #1
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Venting Zoom Lenses

Hi Folks

Some time ago when I bought my first "dust resistant" lens, the PENTAX 60-250, and stuck it on my weather sealed K-7 I immediately started to worry. As someone who was always good at physics (as well as blowing my own trumpet), I immediately realised the problem a pumping zoom action would mean to the the camera and the question of dust.

On the one hand tight seals are provided to keep dust out but on the other is it possibly to making the problem worse ? The pumping action of zooms, and in particular long zooms like my 60-250, shifts around a lot of volume of air inside the camera and it has to go somewhere. Is it possible that the few gaps through which negative/positive air pressure can now vent is making sucking in dust worse? Because air pressure will increase around those few small gaps it can find. (And thereby increasing the power to suck in more dust).

I took out the little microphone rubber stopper and moved the zoom in and out with the opening close to my ear. Good lord, the amount of air coming through this little hole I reckon would be enough to pump up a bicycle tube and the camera sounded like it suffered a bad asthma attack. I also figured all this compressed rush of air can't be good for some of the more delicate parts inside the camera.

So then I got thinking, wouldn't it be good if I kept this microphone hole open all the time, this way at least I have control over where the air flow takes place. (And I have never made use of a microphone, so I don't really need it). And as I am not only good at physics but am also a good thinker (that trumpet again) I thought wouldn't it be good if I could provide a small air filter for this mice hole to allow air to move freely and also keep out dust. And here is what I came up with.

Parts you need:
Small piece of masking tape
Three hole punches, inner Ų 10mm, 8mm and 3mm
A piece of release paper (say from a band aid or sticky label)
A small piece of filter paper from a dust mask
A steady hand, its going to be fiddly

Stick a piece of masking tape on the release paper, put it on a piece of timber masking tape up, take the 10mmŲ punch and knock out a disk, put the disk you just punched out on the timber and punch a hole in the middle with the 3mmŲ punch.

Now take the 8mmŲ punch and knock out a small disk from the filter paper. Peel off the masking paper disk from the release paper and stick this little filter paper disk over the punched out hole of the masking paper. You may need a pair of tweezers for this.

Next stick this over the microphone hole. The pictures provided are pretty well self explanatory.

To test the filter hold the camera with the mice hole close to your lips and pump away (the zoom that is) and if you can feel the air flowing you have succeeded. This means most, if not all, air will now pass through this hole as long as the little filter paper disk is not too thick in which case it will restrict air flow.

I don't really know if all this is working as far as dust filtering is concerned but I feel I have at least done something.

Greetings from sunny Melbourne


Last edited by Schraubstock; 07-24-2011 at 03:10 AM.
03-30-2011, 11:59 PM   #2
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QuoteOriginally posted by Schraubstock Quote
Good lord, the amount of air coming through this little hole I reckon would be enough to pump up a bicycle tube and the camera sounded like it suffered a bad asthma attack.
I think you are blowing things a bit out of proportion, if this was really a problem others would have noticed this long before you have. I use a Sigma 100-300mm f/4 APO EX DG on my K10 and K7 and although this lens isn't weather sealed to the same extent as the SMCP-DA 60-250mm f/4 - it is capable of moving quite a bit of air. I use the sigma 100-300mm f/4 quite a bit and I haven't noticed any increase of particulate matter appearing on the cover glass over my K-7 sensor.

Though on my Nikon D3s which is a magnet for dust bunnies whether I use primes or zooms I still have to clean the sensor after a day of shooting - even if I keep the same lens on it.

I think the coatings pentax use on the cover glass over the sensor are really effective, I only have to clean out my pentax cameras perhaps once a week, even under heavy usage conditions.
03-31-2011, 12:08 AM   #3
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I think blowing things out off proportion (pun intended) is the right term here lol.
03-31-2011, 12:33 AM   #4
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You could be right, but I know my camera is breathing a little easier now.

And I would not be surprised if in future camera manufacturers recognize this and provide pressure relieve valves as weather sealing bodies and lenses become more popular.

Greetings

03-31-2011, 12:39 AM   #5
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QuoteOriginally posted by Schraubstock Quote
I would not be surprised if in future camera manufacturers recognize this and provide pressure relieve valves as weather sealing bodies and lenses become more popular.
My Canon 1Ds MKIII is weather resistant as are many L series lenses
My Nikon D3 and D300s are both weather resistant and many the Nikkor zoom lenses that I use on them are also sealed against the elements.

none of them have a pressure release valve on the camera or lens, so why should pentax cameras have one?
03-31-2011, 01:25 AM   #6
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QuoteOriginally posted by Digitalis Quote

none of them have a pressure release valve on the camera or lens, so why should pentax cameras have one?
I said PENTAX should, did I ?
03-31-2011, 03:33 PM   #7
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Wouldn't they have to be a sealed system if they are to be weather and dust resistant. If you relieve pressure by venting air, you'll need to suck it back in when extending, wouldn't you and that would be when dust gets sucked in.
03-31-2011, 04:20 PM   #8
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Even if you can make your vent dust proof, what about the water resistance? All the WR advantages of the body have just been blown away!
Is dust getting in really a problem? How did the GI who was in Afghanistan get on with his K7 (I think his name was Lee Runge)?

03-31-2011, 05:01 PM   #9
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i for one think it an excellent idea to have filtration of the air that enters and exits the interior of the camera. Properly done it'll reduce dust problems overall.

Kudos to you Schraubstock.

As far as wet weather use, one only has to worry abt ingress of actual wetness. If you're using a zoom lens in the rain then there already is damp air pumping in and out of the camera when you zoom it.

Edit: and think abt it; if in the rain air is being sucked into the camera past the lens seals, it's going to bring in with it what wetness is on the seals that's otherwise blocked.

Last edited by conradj; 03-31-2011 at 06:06 PM.
03-31-2011, 06:33 PM   #10
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QuoteOriginally posted by conradj Quote
i for one think it an excellent idea to have filtration of the air that enters and exits the interior of the camera.
I think we should have airconditioned camera interior, and Ionisation as well to remove the free radicals that will harm the inside the camera. Also a Detox routine.
03-31-2011, 06:36 PM   #11
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Surely Pentax have thought of this? The K-5 weather sealing is based on the K-7, so it's a proven system.

I've heard that there is a vent situated behind the "OK" button on the K-7, so probably similar in the K-5. Maybe this is filtered already?

But if you want to theorise about the physics:

You said yourself that "I also figured all this compressed rush of air can't be good for some of the more delicate parts inside the camera." Well, if you didn't introduce such a gaping hole into your camera body, there wouldn't be all that air whistling around in the camera!

Instead, (if the camera is completely airtight) the air inside the camera gets compressed and uncompressed. There will be a small amount of air circulation around the inside of the camera, but not at nearly the velocity as with your giant hole.

QuoteOriginally posted by Schraubstock Quote
I know my camera is breathing a little easier now.
Your assumption is that the camera NEEDS to breathe. Maybe the camera is designed to be able to handle changes in internal pressure. I don't see why not! I can see how high velocity air movement might be a problem, but changes in internal pressure should be quite ok.

Instead of the camera being completely airtight, there could be some (filtered) venting system, but it might be very small. It could let the air leak out and suck in slowly. Some sort of such venting would be necessary anyway for equalising changes in atmospheric pressure.

If I were you I would not be messing around with it. Your camera didn't evolve by random chance - there was a lot of though and information put into it. Don't think you can necessarily make improvements on it by your uninformed fiddling. You're really disrespecting the Pentax engineers. If you don't believe they can handle such a simply engineering problem, why did you trust them enough to buy the K-5 in the first place?

Not to mention you have probably voided the warranty. If dust/water DOES get into your camera now, you have no one to blame but yourself.

Last edited by secateurs; 03-31-2011 at 06:42 PM.
03-31-2011, 06:52 PM   #12
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03-31-2011, 06:53 PM   #13
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QuoteOriginally posted by selar Quote
I think we should have airconditioned camera interior, and Ionisation as well to remove the free radicals that will harm the inside the camera. Also a Detox routine.
03-31-2011, 06:57 PM   #14
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QuoteOriginally posted by conradj Quote
i for one think it an excellent idea to have filtration of the air that enters and exits the interior of the camera. Properly done it'll reduce dust problems overall.

Kudos to you Schraubstock.

.

So you never change lenses then? or do you do this in a 'Clean room'

03-31-2011, 07:13 PM   #15
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I've seen at least 2 reports of dust developing UNDER the LCD screen on the K-5, possibly due to the use of zooms. Yes, under the screen so I'm not sure how one would clean that. But if it's related to what the OP is talking about, then I hope those of you who are ridiculing the OP will not experience the same problem. :ugh:
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