Lenses

What is the difference between two-touch zoom and push-pull zoom

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There are two basic ways to adjust the focal length of a zoom lens. Some zoom lenses have a zoom ring as well as a focus ring and so are called two-touch. Rotating the zoom ring adjusts the focal length. Other lenses slide in and out like a trombone or telescope; the so-called push-pull design.

 

The push-pull design is more vulnerable to zoom creep than two-touch. This is the problem of the zoom accidentally adjusting focal length (sliding) when tilted up or down because the friction of the push-pull system isn’t enough to counteract the weight of the lens. Push-pulls also tend to suck in a lot of air and therefore dust into the lens when adjusted. However, push-pull lenses can be operated more rapidly, if usually a bit less accurately, than two-touch zooms.

 

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