With vario lenses the focal length can be adjusted within a certain range, which changes also the angle of view. The range in which this is possible is normally not so large as with zoom lenses. In addition the focal plane shifts when the focal length is changed, so that a manual correction of the focus might be necessary. Due to this fact vario lenses are often used in a similar way as fixed focus lenses and the angle of view is adjusted once before use.
Because of thier rather simple internal structure vario lenses are normally less expensive than zoom lenses or even as respective lenses with fixed focal length.
Details can be found in the official Pentax catalogue
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