Every time someone asks me for a kit recommendation I point them towards some sort of prime lens with a standard focal length. Similarly, almost anyone I talk to about the ideal budget kit swears that fixed lenses get much better quality photographs than similarly priced zoom lenses.
What factors contributed to the revolution of the default 'kit' lens changing from a 50mm prime to a zoom lens in consumer and prosumer grade cameras. Why wasn't the 50mm replaced by the 35mm lens, which would be standard on a crop sensor? I am interested to know from a manufacturing and distribution point of view why broad range variable zoom lenses replaced the default SLR lens.
Answer
Presumably because the people who buy their first DSLRs mostly come from the point-and-shoot world and care about the versatility afforded by the zoom more than about image quality. Also, a 50mm is way too long to be a good "default" lens with an APS-C camera, and good-quality ~30mm lenses are, due to certain quirks of optics, much more complex (and thus more expensive) than 50mm ones.
Also, the sort of image quality now common even in cheap kit lenses was simply not possible to achieve in an affordable zoom a few decades back. A prime was back then pretty much the only option.
EDIT
To elaborate on what I meant by "certain quirks of optics", lenses with focal length shorter than the flange focal distance (or register distance) have to employ a special retrofocal design to make the optics work out. This basically entails adding a reverse telephoto group in the rear of the lens. The register distance of the Canon EF and EF-S mounts is 44 mm; Nikon's F mount has 46.5 mm.
This question has a good answer by Matt Grum with some illustrative pictures.
An APS-C camera could probably be designed to have a correspondingly shorter register distance, but it would be incompatible with lenses designed for full frame.
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