lens - What are the pros and cons of non-extending zoom lenses?

Apart from the obvious benefit of not changing the center of gravity, what are the technical pros and cons of zoom lenses that do not change "physical length" when changing the focal length?

For example, are they more or less prone to mechanical failure? More or less prone to attract dust in dirty environments? etc..

Answer

The benefits for a non-extending zoom are:

• Can typically be fully moisture and dust sealed.


• Do not suffer from zoom-creep, where the lens slowly starts to extend when gravity is pulling on it. Some lenses (like the Canon 100-400) have a way to increase tension to minimize this, but this is the exception to the design.


• No change to physical size (this is kind of obvious).