Westminster fountain at sunset

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I would like to know why motorized zoom (controlled by a W/T lever) is always on fixed-lens cameras and never on interchangeable lens cameras.

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5 Answers 5

up vote 10 down vote accepted

I think it's mostly to do with how you hold the camera, most people hold small pocket P&S cameras by the body with both hands. It would be fiddly to try and reach round for a tiny zoom ring on the lens (which is delicate enough without people trying to grab and turn it). Also the zoom ring would have to be incorporated into the collapsible lens assembly, which would be harder than merely including a motor.

With an SLR most people grip the body with their right hand, and support the lens with their left. Given this setup it's easy to zoom the lens manually, making a zoom motor redundant.

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But what about bridge cameras? They are not small or fiddly. –  William C Sep 22 '11 at 22:53

I'm going to take a guess, but the main reason will be Cost. If every lens had to have it's own bulky zoom mechanism the cost of the lens would rocket. Also every camera would need a compatible interface with the zoom mechanism. Also motorized zooming is slow, and the kind of people who use interchangeable lenses are not going to want slow zoom.

I can only see downsides to having it motorised on interchangeable lenses. On fixed lens cameras though, the lenses are often too small and fiddley to accurately zoom because sensor sizes are smaller, and with usually only a live view screen to look at, motorised zoom makes more sense.

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But what about bridge cameras? They are not small or fiddly. –  William C Sep 22 '11 at 22:54

There are actually interchangeable lenses with motorized zooms, for example Panasonic LUMIX GF3X. The reason it uses motorized zoom is to cut size and cost. Hand-rotated zoom tends to be faster and without discrete steps, but the zooming ring takes space and adds to the cost.

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I had motorized zoom lenses on the Minolta Maxxum (Dynax elsewhere) xi series, and it had its advantages and disadvantages. The disadvantage, as has been noted in other answers, was that zooming was slower and less precise than manual zoom. (Remember that lenses on SLRs tend to be bigger and heavier than lenses on compact cameras.) There was one big advantage, though, and that was that the lens could be set to zoom according to the focus distance, maintaining the size of a moving subject automatically.

The feature was only ever available on relatively "slow", inexpensive consumer-level lenses in the dying days of the 35mm film era, so I don't know if it can be said that it was given a fair shot at life. I found the zoom speed annoying for single shots, but the autozoom paid for itself several times over shooting runway fashion. I would love to have seen something more responsive on faster lenses, but Minolta was in trouble at the time and photography was in the process of reinventing itself for the digital era. I wouldn't be surprised to see something like that technology re-emerge, but I'd expect it to be very much a niche product.

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Typicaly:

Mechanical Lenses: Infinitely precise, fast, quiet.

Electronic Lenses: Discrete steps, slow, noisy, smaller.

The former is obviously most desirable. This is why DSLR lenses are almost always mechanical where performance is prioritized over size and cost.

Electronic zooms have the advantage of being smaller and allow a completely retractable design which is used to make most fixed-lens cameras small.

As usual, there are exceptions since electronic zooms can be made to operate smoothly and at a controlled speed which is actually better for video since one sees the zooming in progress. Very few fixed-lens cameras have mechanical zooms which is truly a shame. Presently, Fuji is the only one to still do it.

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Why is motorized zoom always on bridge cameras, then, except those you linked to? –  William C Sep 22 '11 at 22:54
    
See paragraph 5: The electronic zoom allows for a completely retractable design which makes cameras smaller. And paragraph 6: Electronic zooms have an advantage while shooting video since they can advance more smoothly. –  Itai Sep 23 '11 at 0:42

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