Dust On Sensors - The Other Culprit

It is common knowledge that changing lenses on a DSLR is one of the major causes of dust getting into the insides of the camera body and eventually into the sensors. There is another culprit. The extendable ZOOM LENS barrel.
As the barrel extends on the zoom lens, the internal cylinders are exposed. If the environment is windy or dusty, tiny particles can accumulate on the exposed internal barrels. When the barrels are retracted, the dust particles clinging on the cylinders gets inside the lens. The next time the lens is EXTENDED, the change in pressure forces outside air into the lens along the sides of the extending cylinders and BLOWS the dust inside the body!
Doing this a few times on a windy, dusty environment can exhibit a significant amount on captured dust into the lens innards and into the reflex mirror and finally into the sensors.
Some tips:
Check the exposed cylinders for dust before retracting, if on a dirty environent.
Wipe, never blow, dust from the exposed cylinders. Blowing will only push the dust inside!
Zoom slowly, if possible, because zooming quickly and abruptly sucks in more dust.
Expensive tip:
Use a zoom with internal movement. Internal focus and internal zoom movements minimize the dust invasion.

Good point. All my lenses are internal zoom and focusing except myTamron 28-75 2.8 and unfortunately it is my main walk around lens. i'm looking to eventually get the canon 24-70L but hard to justify that expense right now . . .
Good post

Canon 24-70 L is external zoom too.
I really notice this after using the Canon 100-400 L that's a huge dust pump.
My 70-200 L is the only internal focus internal zoom that I have.

Another thing to watch for is Rain, on an external zoom like the 100-400 rain on the barrel is fine when zoomed to 400mm as it stays on the barrel and can be wiped dry. DO NOT make the mistake I did and zoom the lens back 10 100mm in the rain without cleaning and drying the barrel. Took several hours with a hair dryer (on cool. not hot!) to clear the water out of the lens internals :(

Same would go for the Sigma 80-400 as the wet barrel with that lovely matt (almost flocked) coating takes the water back into the lens body.

The 24-70 L if you use the lens hood, is safer because the zooming extension is inside the lens hood and would be somewhat protected. But I bet you could get it wet if you try.

Oh no, I did not realize it was external zoom. hmmm something to consider.

I use my 24-70L in rain and in dusty environments, including salty environments like the sea. Never had a problem with moisture in either the 24-70 or the 100-400 lenses. Dust on the prism is more of a problem but I think that comes in from changing lenses, but a quick rocketing sorts that out so far.

The sealing on the lenses I have must be working well?

Paul, remember the weather at Kew and the 5D with the 24-70 was out in all that rain and moved from cold to hot environments with little problems.

Roger R.

I should have tucked my camera in my coat like you did.
Keeping it out to photograph the birds on the lake meant it was nice and cold in the palm house :(