Six months ago an over-eager hotel porter in Sri Lanka grabbed my camera bag before I could stop him and dropped my wonderful 100-400 lens a bit less than half a metre onto a concrete path. It landed almost vertically, on the rim of the rear lens cap. A few hours later I flew home with it, not knowing if it was damaged or not.

So it sat here unused. I really didn't fancy having to send it off to be mended and I simply used the 600/4 and the 24-105 for a while. I did pick up the 100-400 just once to grab a quickie of a rare (for Tasmania) bird on our dam. It made a nasty crunching sound, missed focus, and the bird flew off. So I put it to one side again, intending to test it properly and (probably) send it off to Peter at Accurate Instrument in Brisbane before Christmas. But I didn't get around to it.

Finally on New Year's Eve I went out for a drive and took the 100-400, planning to try it out.

It seemed to be OK. No strange noises, the IS seemed to be working.

In the end I gave it a solid workout, taking about 600 shots.

It's either perfectly OK or else nearly OK and not quite right. I'm not sure yet. The day's pictures are OK, not great, but I'm out of practice with the 100-400 and I was using the 5DS (which isn't quite as good as the 5DS R) and the light was pretty harsh. I will have to test again under perfect lighting conditions to be sure it is really OK.



And there was one other reason the pictures might have been a bit sub-par. For most of the day I did something I almost never do - and regularly advise people against. I put a 1.4 teleconverter on the 100-400.

I've tried teleconverters on 100-400 lenses before, of course, though with older cameras - certainly the 1D III and most likely either or both of the 1D IV and the 7D II as well. I took the view at that time that the teleconverter wasn't really improving the reach of the camera - what you gain in raw magnification you lose in slower, less reliable AF, and inferior optical quality.

What about with the 5DS? Well, it focuses remarkably quickly at f/8. Centre-point only, of course, but none of that slow hunting we used to get with an f/8 lens back in the old days. As for accuracy, well it's not bad. But not nearly as good as it is bare lens.

All-in all, I'm less violently opposed to using a TC on an f/5.6 lens than I was, but I wouldn't really call it an unqualified success.

Here is an example.



(420mm, f/10, 1/640th.)

It's not bad but it isn't the standard I'd expect from a 100-400, let alone a big prime.

Worth using? On balance, probably not. There are times when I'll put a 1.4 on a 600/4 prime - 90% of the time I go bare lens which really is better if you can manage it - and there are even very rare times when I'll use the 2.0 converter on it, but you have to have really, really good light and a very solid stance. (A windy day, for example, rules that right out.)

The number of picture I reckon are good enough to bother putting on my website tells a story: currently 186 with the 600/4 bare lens; just 20 with the 1.6 added, and only 5 with the 2.0. I'm surprised it is as many as 5 actually.

With the 100-400, however, it's a rather different question. First, if you don't have something like a 600 you are hungrier for more reach. But against that, teleconverters essentially work by trading image quality for magnification. With a zoom lens, even one as astonishingly good as the 100-400 II, you have less quality to trade off before the image shows the impact. And thirdly, focus become more of an issue. Focus is tricky with ANY long lens of course, but becomes much more difficult with small maximum apertures. SLRs focus by comparing the difference between different light paths through the lens, and with the f/8 maximum aperture of a 100-400 with a 1.4, that difference is minimal. This is one place where mirrorless cameras have an advantage - they focus better with slow lenses. (But given their many disadvantages, it might be a very long time before I buy another.)

On balance, I reckon the 1.4 is usable on a 100-400 but best avoided.