Lenses that push air

Good day all,

I've been reading through the various threads in this DSLR forum and found something rather surprising to me at the end of the one title "Anyone used the Canon 28-300?" when Scott Hughes made the comment that some lenses can "push" dust into the camera chamber. That statement surprised me so I did a test with my Canon EFS 17-85mm f/4-5.6 IS USM lens and sure enough, it pushes air out the back side of the lens. Which answers some sensor dust questions I've had in my mind for quite awhile.

But my question this time is this. If some lenses can push air out the back it seems logical they will also draw air back into the lens. Assuming that's true, do such lenses need to be periodically sent to a service facility for removal of dust particles inside the lens?

Thanks.

As far as I know, no commonly available lens is totally sealed and they all have moving elements inside for focussing or zooming. So, they all "push air" and therefore get dust and other crud inside after some usage. How much depends on how much use they get and the environment they're used in.

Unless you see a degradation in your pictures that's not explicable by other factors, don't worry about it.

JohnZeman said:

But my question this time is this. If some lenses can push air out the back it seems logical they will also draw air back into the lens. Assuming that's true, do such lenses need to be periodically sent to a service facility for removal of dust particles inside the lens?

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I would worry more about where you change your lenses, than the lenses outside of very dusty environments like playas.

As to the service center, sensor cleaning is relatively easy to do at home. I use the Copper Hill Images wet cleaning set (link) whenever my sensor gets too dusty. Albeit, cleaning your own sensor likely voids a warranty or some such, but it is not hard to do. But you can break your camera doing it incorrectly.

enjoy your day,

Sean

JohnZeman said:

Good day all,

But my question this time is this. If some lenses can push air out the back it seems logical they will also draw air back into the lens. Assuming that's true, do such lenses need to be periodically sent to a service facility for removal of dust particles inside the lens?

Thanks.

Click to expand...

Hi John,

Assume all lenses get air and dust in the chamber. It's just a fact of life. But so does the working of the moving parts of the camera, the miirror and shutter.

Also at wider apertures the dust does not show.

As Sean stated, it's the lens change where you are at most risk. Always blow lens being added with the Rocket blower and hold camera upside down for the change!

If you shoot with smaller appertures one just has to clean more regularly, which frankly I don't.

My 1DII has had 3 cleanings my 5D one for all the thoudands of shots I have taken.

So as a result of this reminder, I'll do another cleaning.

asher

Thanks guys.

I have the sensor clean/sensor brush cleaning systems and have a pretty good routine down on cleaning the camera sensor regularly. So sensor dust isn't often a problem for me. I was mainly concerned about something mostly out of my control, that is whether the internal workings of the lens itself could develop dust problems. I can't say I've ever noticed a problem with dust inside of a lens but wanted to ask in case it is for some others (so I could be aware of that possibility).

I'm always careful and aware of the current conditions when I switch lenses, but I can't say I've used my rocket blower on the lens before I've made the change. That's some more good info to know.

Much appreciation for the info.

John,

In most cases, a few particle of dust will not cause image degradation. Of course we don't like it. What is really bad is fungus in humid climates or moisture when a cold lens is brought in to a humid room.

In each case the problem is moisture. Cold lenses must be bagged (ziplock baggies, use two for safety) and when the lens is at room temp it can be removed.

In moist climates lenses should be stored in a chamber with dessicant. Otherwise one can get packets ofdry silica cristals to drop into the plastic bag before sealing the ziplock.

Dust is way down the list for worrrying, except in Iraq, where you know the dust will get in and the lens will have to be cleaned! So generally, either it's nothing to worry about or you're screwed. Anyway, that's my take!

Asher

Asher Kelman said:

Dost is way down the list for worrrying, except in Iraq, where you know the dust will get in and the lens will have to be cleaned! So generally, either it's nothing to worry about or you're screwed. Anyway, that's my take!

Asher

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It is interesting how different we 'rate' dust. Sensor cleaning is part of the routine for us, but we make multiple lens changes and aren't in a clean room!

My approach is to shoot and worry about the other stuff later.

Scott B. Hughes said:

My approach is to shoot and worry about the other stuff later.

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The only time I worry about dust is when shooting macros or when I have huge dust bunnies on the sensor. At f/14 at 1:1 to 1:2 sensor dust matters in out of focus image regions. At f/8 sensor dust is a minor issue. At wider apertures it tends to be a non issue most of the time.

I know I have only cleaned my sensor once or twice in the last 3 months and I change lenses in bad places at times.

As to playa dust, it will be a part of your life for years unless you throw away everything you took onto the playa and get hosed down in a clean room (I know I have some stored in many locations). Playa dust would definitely be a first tier source for ruining an unsealed lens by making it a dust gun firing at your sensor every time you focus.

enjoy your day,

Sean

Sean DeMerchant said:

The only time I worry about dust is when shooting macros or when I have huge dust bunnies on the sensor. At f/14 at 1:1 to 1:2 sensor dust matters in out of focus image regions. At f/8 sensor dust is a minor issue. At wider apertures it tends to be a non issue most of the time.

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It all depends on what you're shooting. Most of the time I don't worry too much about dust. I don't seem to accumulate very much, so it's not a big worry.

Every once in a while I'll go out, shoot 200 frames and have to clean up one or two really egregious dust spots on every one of them. This can seem to take hours. I then curse myself, clean the sensor and stop worrying about it until it happens again.

No matter what, dust on a digital sensor is far less annoying than dust on the BOTTOM of the glass on your scanner

I understand that the new series of DA lenses for the Pentax DSLR's will be sealed. This will complement the sealing they incorporated into the K10D design. It's not clear how they will seal the mount....on my K10D I see no provision for a mating O-ring but that's not to say they wont deal with the issue.

Since I am currrently using the kit zoom while waiting for the new series it's not a problem. However, as a precaution I bought a thin, larg diameter O-ring that I slip over the lens barrel at the mount and the roll it down to meet the body after the lens is seated. It also functions as something of a moisture seal as well.

David

John,

in 4 years of working for Canon in the photographic service dept I did not see one lens come in for cleaning of dust from the internal elements. Internal dust would not come into range of focus nor degrade the image......unless of course it was massive. Forget dust, worry about fungus instead.

Cheers,

Paul