Do Zoom Lenses Filter the Air that Enters when Lengthening?

Started 6 months ago | Discussions thread
Gerry Winterbourne Forum Pro • Posts: 18,721
Re: Do Zoom Lenses Filter the Air that Enters when Lengthening?

Chas Tennis wrote:

When zoom lenses adjust by motor or are adjusted by hand and the length and volume of the lens increases, air must enter the lens for each operation. My compact zoom lens telescopes down and withdraws into the camera body. What's done to keep air particles out of the zoom lens?

Nothing keeps air out; if it did you'd be fighting against vacuum every time you tried to extend, and against internal pressure when you try to withdraw.

One serious problem with automatic motorized zoom lenses is that one day the lens may fail to operate. Might that be often due to particulates in air building up in the mechanism of the lens?

Possibly but It's unlikely to be the main cause.

Also, dust would accumulate on the lens surfaces inside the zoom lens.

What is done to filter the air that enters zoom lenses every time their length increases?

Generally speaking, nothing. Weather resistant lenses have ring seals that fil the inevitable gaps between the sections of barrels. These are designed to exclude liquid water but help with all but the finest dust.

More important than dust is moisture: the same pumping action draws water vapour into the lens and that can condense, leaving droplets of liquid water anywhere inside the camera. This is why manufacturers won't guarantee weather resistant lenses against internal water damage.

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First camera 1953, first Pentax 1985, first DSLR 2006

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