Where does the air come from....

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I have searched around for this online but it is a difficult search to compose.

So, take the 100-400mm Canon L lens. There is clearly a huge amount of air that needs to fill it between 100mm and 400mm (hence "Dust pump"). But what I am wondering is... where does this air enter the lens?

I don't mean this lens specifically, I am talking all lenses that aren't fixed length.

Does it just come through between the barrels? But aren't some extending lenses weather sealed?
What about the camera body... is the air pulled from in there? But then it's going to get the mirror box dusty when it needn't.

Any ideas guys?
 
I think lenses have to take air in and out otherwise I reckon otherwise compression would be an issue - unless a vacuum is possible? I'm no physicist though lol.

I think the more expensive lenses only take air in and out of the camera chamber and hopefully none of the lenses suck air in from outside and then expel the air inside the camera! lol
 
No a vacuum wouldn't be possible. 1 atmosphere of pressure is the same as 10 metres of water (1 bar). So a vacuum would pull the lens closed as if it had 10 metres of water pushing on it.

But if they did pull and push air through the camera chamber, then the air must be entering and exiting the camera somewhere....
 
if they were really clever, they would suck air from camera body then expel through lens barrel, so automagically removing dust as you use it.
hmm :thinking:now how do you take out a patent:lol:
 
vizzair said:
if they were really clever, they would suck air from camera body then expel through lens barrel, so automagically removing dust as you use it.
hmm :thinking:now how do you take out a patent:lol:
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Ah.. but where does the air enter the camera?
 
Perhaps Dyson should look into the lens business? hehe
 
Jez2011 said:
through the gaps?
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Well yes. But is there perhaps a designed location for the air to enter? Perhaps a small foam filter? This problem MUST have been considered by the designers. I just can't imagine a solution for a weather sealed body and lens.

Anyone with the 100-400mm prepared to "pump it" and feel for air entering/escaping the camera and/or lens?
 
Very interesting question (because I'm a sad engineering type) and something I've not thought about previously, but now you have brought it up I'm keen to see if anyone has the definitive answer. :thinking:
We manufacture bellows which sometimes have to have small filtered holes to allow air in and out during compression/extension, but no idea how it works on the lenses.

Gareth
 
wippers said:
Very interesting question (because I'm a sad engineering type) and something I've not thought about previously, but now you have brought it up I'm keen to see if anyone has the definitive answer. :thinking:
We manufacture bellows which sometimes have to have small filtered holes to allow air in and out during compression/extension, but no idea how it works on the lenses.

Gareth
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Nothing sad about engineering! (I hope) I actually started thinking about it because I am currently revising for an exam on Turbomachinery.... not that jet engines have much in common with camera lenses.....

Now if I could just find someone who would cover their camera and lens in talcum powder....

Or there is always the old bike inner tube trick!! Put it underwater and see where the bubbles come from...
 
If it's a push pull lens then isn't the air sucked in around the lens barrel itself? That can't be airtight as otherwise it wouldn't move at all. I've only ever used a cosina one briefly.

Smoke might be better than talc.
 
srichards said:
If it's a push pull lens then isn't the air sucked in around the lens barrel itself? That can't be airtight as otherwise it wouldn't move at all. I've only ever used a cosina one briefly.

Smoke might be better than talc.
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Smoke would be better but you wouldn't want either in your camera..

Actually it must be the lens barrel, else putting a lens cap on would stop it being possible to adjust zoom and as far as I am aware this isn't the case. It certainly isn't with my 24-105.

Maybe some lenses have a diaphram in so that no new air enteres the actual lens. I can't help but think that the volume of air taken in by extending lenses would draw in more dust than it does if the air comes from around the barrel without some protection.
 
Anybody know how to get flour out of my 100-400 lens ?
 
whom said:
Actually it must be the lens barrel, else putting a lens cap on would stop it being possible to adjust zoom
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Only if the lens cap is airtight - which I doubt...
 
dinners said:
Anybody know how to get flour out of my 100-400 lens ?
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Yeah, use some smoke. If that doesn't work run it under the tap :thumbs:


hunnymonster, I reckon the lens caps are pretty close to airtight. Well, close enough that if you zoomed the lens in and out with it on you would hear the air escaping.
 
Using only the air in camera chamber allows weathersealing surely? I'm also wondering if holes can be made small enough to allow air but not big enough to allow the majority of dust particles?
 
Most zooms dont change length or volume when zooming because they internal zoom.

The 100-400 takes it in around the barrel and the body hence the reason it can pump in air. Because it's an external zoom not internal it has to compensate for changing volume.
 
gman said:
Using only the air in camera chamber allows weathersealing surely? I'm also wondering if holes can be made small enough to allow air but not big enough to allow the majority of dust particles?
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But if you're taking air out of the camera then air has to enter the camera. The volume of the entire system increases and therefore so much the air. What you are suggesting is a filter... Foam has this effect that you speak of.
 
Maybe the air thins? lol
 
gman said:
Maybe the air thins? lol
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Decreasing pressure would be possible but you would know about it. The lens would slam itself back again because the air would act exactly like a spring.
 
Air gets in/out anywhere it can, but lenses are mostly designed to 'breathe' around the front. Stick a poly bag on the front, sealed with rubber bands, and you can see it.

It keeps grud away from aperture and IS mechs, and is easy to clean. Just drop out the front element group, which is where most of it usually collects.
 
Given that the end of the lens that attaches to the camera is full of glass, and not airholes, I think it's reasonable to assume that lenses that change length when being zoomed don't draw air through the mirror box of the camera, but through unsealed parts of the lens itself.
 
The lenses do change the amount of air within them and the extra air enters and exits through the camera body as far as I'm aware as weather sealed bodies are not pressure sealed hence they can't handle being submerged in water. On the Olympus E-3 you can see the air vent under the CF door as a row of small circular holes at least that's what I've gathered from previous discussions on the issue and it seems plausible.

John
 
First things first. Thanks for all the responses! HoppyUK I like you idea about the bag. But air can't escape around the front element, especially not with filters on. Scarecrow, the rear end has lots of air space and is not full of glass on zoom lenses. JohnMcL7, I had a feeling it was the camera body due to my impression that lenses had better sealing than bodies.

But I think there have been too make theories spoken with authority directly contradicting each other. Therefore I decided to test it for myself! Using HoppyUK's idea with a bag I tested my only extending lens, the 24-105mm. Here are the videos on youtube.

http://www.youtube.com/watch?v=TAEZB-C7wJM&feature=player_detailpage

http://www.youtube.com/watch?feature=player_detailpage&v=tOgHTYta9aw

You can see for yourself the results. Air doesn't come out from the barrel even with the cap on. I believe air escapes from around the zoom and focus rings when the cap is on, and you can hear the air escaping in the video. When on the camera, air comes in and out through the camera.
 
whom said:
I have searched around for this online but it is a difficult search to compose.

So, take the 100-400mm Canon L lens. There is clearly a huge amount of air that needs to fill it between 100mm and 400mm (hence "Dust pump"). But what I am wondering is... where does this air enter the lens?

I don't mean this lens specifically, I am talking all lenses that aren't fixed length.

Does it just come through between the barrels? But aren't some extending lenses weather sealed?
What about the camera body... is the air pulled from in there? But then it's going to get the mirror box dusty when it needn't.

Any ideas guys?
Click to expand...

Moving the zoom back and forwards moves the rear lens elements. Because you can do it fast with the 100-400 it can blow dust already in the mirror box around. I never had a problem with the 100-400 on my 40d
 
Interesting question. But if they sucked in air, that would include an amount of water vapour, so surely you would end up with misting/condensation inside the lens.
 
whom said:
First things first. Thanks for all the responses! HoppyUK I like you idea about the bag. But air can't escape around the front element, especially not with filters on. Scarecrow, the rear end has lots of air space and is not full of glass on zoom lenses. JohnMcL7, I had a feeling it was the camera body due to my impression that lenses had better sealing than bodies.

But I think there have been too make theories spoken with authority directly contradicting each other. Therefore I decided to test it for myself! Using HoppyUK's idea with a bag I tested my only extending lens, the 24-105mm. Here are the videos on youtube.

http://www.youtube.com/watch?v=TAEZB-C7wJM&feature=player_detailpage

http://www.youtube.com/watch?feature=player_detailpage&v=tOgHTYta9aw

You can see for yourself the results. Air doesn't come out from the barrel even with the cap on. I believe air escapes from around the zoom and focus rings when the cap is on, and you can hear the air escaping in the video. When on the camera, air comes in and out through the camera.
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When the lens is mounted, ie semi-sealed at the rear, most of the air comes in/out around the front of the focusing ring. I have the same lens. That's what I meant.

Where it goes then is harder to check, but dust particles almost always ends up behind the front element group.
 
Fotografia, they do suck in air, there is no getting around that. Any lens that changes volume must suck in/blow out air. I didn't know you had any water vapour in Cyprus...

HoppyUK, I see what you mean now. I wonder how sealed you can consider the mirror box to be though. I know you only said semi sealed but from the noises the escaping air was making as it came out from the focus ring I imagine that is a better seal than the mirror box. I wonder if the mirror boxes are designed to let air in and out because sealing them completely would probably be easy. Perhaps the air passage is the cause of the 5D3 "light leak" issue? Who knows...

Thanks Musicman, mods please close this thread, we have an answer :thumbs:
 
whom said:
Fotografia, they do suck in air, there is no getting around that. Any lens that changes volume must suck in/blow out air. I didn't know you had any water vapour in Cyprus...

HoppyUK, I see what you mean now. I wonder how sealed you can consider the mirror box to be though. I know you only said semi sealed but from the noises the escaping air was making as it came out from the focus ring I imagine that is a better seal than the mirror box. I wonder if the mirror boxes are designed to let air in and out because sealing them completely would probably be easy. Perhaps the air passage is the cause of the 5D3 "light leak" issue? Who knows...

Thanks Musicman, mods please close this thread, we have an answer :thumbs:
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I'm not sure that any camera or lens is truly hermetically sealed. They are light-tight and that's what matters. 5D3's issue is a minor internal light-baffle thing related to the display illumination, which is right next to the metering sensor.

Weather-sealing doesn't mean water-proof of course. The Canon 24-105L that we both have is claimed to be weather-sealed, but it's clearly not hermetically sealed. I guess that if there is sufficient distance between the internal workings and the point at which rain can fall, ie shielded rather than sealed, it's going to be fairly water resistant in normal conditions. Bit like an umbrella.
 
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Some lenses have incredibly small heating and cooling mechanisms. Air is cooled when retracting and heated up when expanding the lens. Cooler air takes up less room that hot air.
It is not really surprising that some lenses cost so much.
 
whom said:
Fotografia, they do suck in air, there is no getting around that. Any lens that changes volume must suck in/blow out air. I didn't know you had any water vapour in Cyprus...

HoppyUK, I see what you mean now. I wonder how sealed you can consider the mirror box to be though. I know you only said semi sealed but from the noises the escaping air was making as it came out from the focus ring I imagine that is a better seal than the mirror box. I wonder if the mirror boxes are designed to let air in and out because sealing them completely would probably be easy. Perhaps the air passage is the cause of the 5D3 "light leak" issue? Who knows...

Thanks Musicman, mods please close this thread, we have an answer :thumbs:
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I accept they must vent in some way, but I can't quite understand why they don't continually fog up on the inside.

And there is plenty of water vapour here in Cyprus, the dams are overflowing, no drought here. :lol:
 
Hahaha very funny Ernesto! That would be one solution yes.

Fotografia, you may be laughing now but I've been told Cyprus bought water in the past and by the time it arrived on ships it had gone stagnant... I don't know why they don't fog up, that is part of the reason for starting this thread. Finding the source of the air and if it is filtered.

HoppyUK, I know they are not completely sealed. I too imagine the designers aim to give as much distance between glass and air entry point as possible. Lets say that when zooming out you draw in X volume of air. If, between the nearest element and the point of air entry, there is say 10X in air volume then there is a very slim chance of the air you draw in ending up on the element. Instead, all the crap would be near the entry point.

I realise where the metering sensor is now, thanks for the explanation.

If I were to design around the problem of sealing and volume change, I would seal the lens and have a filter before the mirror box with air entering from the side or rear of the body. Probably on the left and low down so that any dust drawn in would have to go uphill (in landscape or portrait) to get into the mirror box.
 
We could always ask Nikon or Canon directly and see if they reply?
 
Come on gman, don't be boring and sensible :P

In the interests of not being sensible. I have covered my 5d2 with cling film and can now confidently say that:

The majority of the air that enters and leaves the 24-105mm when mounted on a 5d2 come THROUGH THE BODY. This may just be because the lens has generally better sealing than the body. But it IS the case. See video for proof and please bear in mind that the cling film is not covering very well so air is escaping all over the place.

http://www.youtube.com/watch?v=tinaeLM-2WY&feature=youtu.be
 
Haha good shout gman, I think we had every possible option posted by various people, well done on being right!
 
Well, unfortunately I'm not a genius and have a confession to make:

Point 2

:whistling:
 
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