Why is the 100-400 concidered a dust sucker?

what the 100-400 does is blow the dust thats in the mirror box around due the force of air movement generated by the push pull zooming. it does not suck dust in

gjl711 wrote in post #3068788
There have been several threads in which the 100-400 is referred to as a dust sucker and I just read the comment once again in another thread. Since the 100-400 is my next big purchase, it is something of a concern. But how specifically does the push/pull mechanism of the 100-400 suck in any more air than a twist mechanism? Both have extending barrels which will cause the pressure inside the lens to decrease due to the expanding volume thus causing outside air to rush in. If there is dust in the outside air, it will too enter the lens. So the only difference between a push/pull zoom and a twist zoom is that the action used to extend the barrel is changed, not the result of that motion. In both cases air is going to be sucked into the lens. What am I missing? Is this just one of those photo urban legends that if repeated enough becomes the popular truth? Or is there really some design flaw that somehow causes more dust to be sucked in?

poah wrote in post #3070029
what the 100-400 does is blow the dust thats in the mirror box around due the force of air movement generated by the push pull zooming. it does not suck dust in

That's my point also.

In that plastic bag demo - I don't see very much volume of air in the "filled" bag. That doesn't convince me of anything.

I don't know how to test this. What I DO Know is that, I have not felt any problem with my 100-400 regarding dust. I connot tell if the dust shows up from the lens, more likely when changing the lens, or what. I just clean the sensor a couple times a year if it shows spots. I have not felt the lens caused any more dust than any other lens. FWIW Seems to me the problem is rare considering the overall usage of this very popular lens. (There is good reason for it to be poopular, It works very well)

SaSi wrote in post #3068835
One of the reasons that made me choose the Sigma 80-400 over the Canon 100-400 was the push-pull zoom action that is very widely said to be (1) odd, and (2) suck dust.

Honestly, I "used" these two rumours, along with a $400 price difference, to justify my selection of the Sigma over the Canon L.

After using the 80-400, a lens that has an equally large barrel that extends very significantly during zooming, I can say that partly, the zoom action is delayed by the amount of air that travels in and out of the lens. When turning the zoom ring as fast as I can, I can actually hear the sound of the air as it travels through the small vents that have to be built into the lens design, just to allow zoom.

I come to the conclusion that the only lenses that don't actually suck/blow air are the ones that employ inner focus and inner zoom (i.e. expensive L grade lenses that don't extend during zoom/focus and can be made weather sealed).

this is a very astute conclusion that I happen to agree with.

Push pull zoom has it's detractors, but the simple fact is it allows you to change focal length MUCH faster than any other zoom method does, and once mastered, with far more freedom of control.

Mine gets a little more dust than the other lenses, but nothing terrible

Mine gets absolutely no more, or less, dust than any of my other lenses.

It's a nonissue as far as I'm concerned.

As to the push-pull vs. ring, they both have their place and both work perfectly. I don't prefer one over the other.

mark

RikWriter wrote in post #3069950
Sorry, but that's an unwarranted assumption on your part. I don't "use the zoom as a pump," despite your contentions otherwise.

Really?

Your own words were:

RikWriter wrote in post #3069950
Now pick up the Canon and zoom it out, then in as fast as you can. Zoooooom/Whoooosh.
It sucks in more dust because you can (and probably will) extend and collapse it faster.

Do that, and you deserve all the trouble you get: don't do it, and there's not a problem.

Keith R wrote in post #3074392
Really?

Your own words were:

Do that, and you deserve all the trouble you get: don't do it, and there's not a problem.

That's quite a leap of logic, from me saying "it is different from a twist-zoom because you CAN pump it quickly to you assuming that's how I use it. If you'd paid attention to my posts, you'd see that I said already that I took special care to zoom it in and out slowly.