Why does focus change if I focus at one focal length and then zoom to a different one?

Why does focus change if I focus at one focal length and then zoom to a different one?

Most AF zoom lenses designed for DSLR stills photography are varifocal, rather than parfocal. This means they are not designed to retain focus throughout the zoom range and there is likely to be some shift of focus when zooming, which is perfectly normal. Designing them as parfocal would mean big compromises in terms of size and price, and generally users of such lenses do not require it because they use the AF function, so the focus shift is of no consequence.

Where parfocal lenses may be needed is in video production/cinematography and we would recommend lenses designed specifically for this purpose.

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