[Tannin]

(Wasn't that an animal in the Dr Doolittle books?) But before the inevitable deluge of off-topic replies, on with the meat of my post: the Canon 100-400L f/4.5-5.6 lens and its controversial push-pull zoom mechanism.

I noticed a couple of posters in another thread saying how they considered that lens and decided against it because they didn't fancy the push-pull zoom. I've often seen simalar comments in other fora. And that prompts me to respond with my own feelings about it.

I bought the 100-400 largely for two reasons:

* I wasn't comfortable(after several years of using P&S digicams, mostly digiscoping) with the idea of a fixed length lens. Would it feel very restrictive, not being able to adjust the field of view without moving? (Something you often can't do with birds and wildlife.)
* Image stabilisation. If it wasn't for the IS, I would have gone with an f/5.6 400mm prime, and taken my chances on the first point.

On the against side, I didn't fancy the push-pull idea. It looked and sounded clumsy and needlessly awkward. But in the end, I bought the pushmepullyou despite the weirdo zoom mechanism.

Sure enough, it felt weird and awkward. The locking mechanism helped, but you needed to set it just so. Wonderful lens, but strange to use.

That initial reaction lasted about two weeks. The push-pull does take getting used to, but now that I've had the unit for a while, I love it. I wouldn't dream of swapping the push-pull zoom for a twist zoom now.

It is miles faster to operate, and simpler too. One thing I have come to mildly hate is the way that different lenses operate in different directions - twist lens A clockwise to zoom in, but twist lens B anticlockwise. I am forever twisting the wrong way when seconds matter and I'm in a hurry. (Which is nearly always with nature work.) The only lens I never twist the wrong way is the 100-400. Push to zoom in, pull to make it shorter. What could be easier?

With no zoom ring, Canon had room to make the focus ring nice and large, and there is none of that hurried fumbling for the right ring you get with twist-zoom lenses (especially short ones).

If you leave the friction ring a bit too loose, it tends to slip out to the 400mm setting. So what? Most people use a lens of this length at the 400mm setting most of the time. (Hey, we all really want a 500 or a 600 but can't afford one yet, right?) So it slips a bit if you don't tighten it, but in general, it slips the "right" way. Often I find that I've set it to 100 or 150mm for a wildflower of something similar, and by the time I am in position for the next bird, it has dropped itself back to 400 - which is exactly where I want it. And if you anticipate doing a series of shots at shorter lengths, just twist the friction ring a bit to make it stay put. After a few days' practice you will find yourself doing this without conscious thought and with one hand.

What about dust? The dust pump argument is a nonsense. A moment's thought will demonstrate that, for any given expansion ratio, a given volume of air must be moved: it doesn't matter if the lens screws out or slides out, it still has to move the same amount of air, and still has to suck in the same amount of dust. The dust question only becomes relevant when you are considering an internal zoom lens of fixed physical length - in which case it applies equally to push-pull or twist-zoom units.

Accuracy? If you often want to zoom to (e.g.) 275mm and not 278 or 269, then the pushmepullyou is probably not for you. You can set it exactly but it's a bit fiddly to do. I can't imagine ever wanting to do this with nature work, however. In the studio, sure - but who uses a 400mm f/5.6 lens in a studio? Mostly you want (e.g.) about 300mm, and 289mm or 304mm will do just fine - but you want it right now (before the bird moves, or the race car goes by). In this context, the fast push-pull is a real winner.

Summary: if you try out the trombone lens for an hour or a day, you will probably dislike it. But try it out for a month or so, get used to the difference, and you might start wondering why all lenses are not made this way.

I'm a convert.