[kypfer]

OK … so my K-5 is Power-zoom compatible and my FA 100-300mm f/4.5-5.6 is Power-zoom capable, but exactly what use is this feature, other than for flattening batteries?
Doubtless I've missed something basic in my limited research, but I don't see what can be accomplished by Power-zoom that can't be achieved quicker and quieter manually.
Looking forward to some enlightenment

[Adam]

You've basically hit the nail on the head, which is why this feature was only around for a short while. I could see how lens retraction might be useful, but probably not worth the added complexity/weight.

If you're interested in a bit of historical context though, the PZ-series film SLRs actually did support 3 additional power zoom functions. Here's a quick overview:
Pentax Lens Power Zoom

[kypfer]

You've basically hit the nail on the head, which is why this feature was only around for a short while. I could see how lens retraction might be useful, but probably not worth the added complexity/weight.

If you're interested in a bit of historical context though, the PZ-series film SLRs actually did support 3 additional power zoom functions. Here's a quick overview:
Pentax Lens Power Zoom

Excellent Thanks for the response!

[Pentax Syntax]

Well one advantage is that AF is triggered during power zoom (at least on the 28-70 FA*). You can zoom and shoot. Very nice for sports.

[ramseybuckeye]

Apparently some people liked gimmicks and added weight to their lenses. I can see somebody at Pentax thinking it was cool on point and shoot cameras so we should do it on SLR lenses.

[Lowell Goudge]

On the PZ1 there were other features as well,

For the creative at heart, you had synchronized zoom with exposure which was interesting for night shots.

You also had image size tracking where as a subject moved towards you the camera would change focal lengths as long as you held the camera with the AF active, tracking the subject to keep it framed at the same size as distance changed.

But on the DSLRs none of this works, the only thing these bodies support is power zooming

[rpjallan]

I actually used the power zoom function on my old Z1. I found it to be pretty good back in the day to be honest. The speed of the zoom changed the more you turned the zoom ring which made it quite useable. I didn't really find it to affect battery life that much. And I did manage to get some good zoom during exposure shots at one time. I remember that I had tried this earlier with a manual zoom and the results were terrible.

[gylfimag]

In theory it may have seemed a good idea but in practice powerzoom really only added weight and made a very loud noise when zooming. The kit lens for my PZ-10 is a powerzoom and I used that pair for a long time but never found the powerzoom useful. At some point the switch on the lens that takes it in and out of powerzoom mode broke and to repair it I glued it stuck in powerzoom mode (not a very elegant repair I will admit). Some regret over that when I bought my first Pentax DSLR as it could not powerzoom (the lens could be used but only as a 50 mm lens). Eventually I got a DSLR that supports powerzoom, the K-1 (I checked!), but its kit lens is much better than this 30 year old film era lens so no use for it now.

[rpjallan]

At some point the switch on the lens that takes it in and out of powerzoom mode broke and to repair it I glued it stuck in powerzoom mode (not a very elegant repair I will admit). Some regret over that when I bought my first Pentax DSLR as it could not powerzoom (the lens could be used but only as a 50 mm lens).

As far as I remember (& I can check later because I still have two power zoom lenses) you actually engaged/disengaged the power zoom by pulling back/pushing forward the zoom ring.

Another handy feature that I can remember using quite a bit is you could set an intermediate focal length & return to it with the push of a button.

[builttospill]

Before I owned any Power Zoom lenses I thought this feature would just be a silly marketing gimmick. Power Zoom is actually great. I use it a lot on my FA* 80-200, occasionally on the FA* 28-70, and wish my F* 250-600 had it like its younger FA* sibling.

When zooming, the lens focuses incredibly fast and accurate. It tracks subjects moving forward and backward with PZ-series cameras very well. When photographing birds in flight I often wish DSLRs supported this feature, especially with bald eagles and the 250-600. I don't know about non-star FA lenses, but FA* lenses have quite a bit of pixie dust: F* & FA* club! - PentaxForums.com

[pentaxus]

For baseball photography you could set up for a play at 2nd base. You could be taking regular pictures and when the play happened you just hit the button and the lens would go to the pre-set shot. You just had to aim.

[mikesbike]

As others have said, when activating the zoom, either to frame your first shot, or to zoom when following a moving subject, the zooming also activates AF, so when you get your framing to take your shot the focus is already achieved. Much lamenting has been written regarding slower AF of Pentax models compared to other brands. However, Pentax AF when using the power zoom feature is very fast indeed!

It does entail a fair degree of noise, and does depend on the camera's battery. Too bad it was not incorporated into some modern lens designs with quiet DC lens motors.

Again as others have said, the full range of power zoom features was exclusive to some film models, especially the PZ-1 or Z-1p, and not available to any DSLR. Power zoom basic function with a PZ lens has only been offered on flagship-level DSLR models.