This week my new mega-expensive Canon 600/4 II arrived. For a short while yesterday (only an hour or so stolen from other duties) and today (most of the day) I got to try it out.

I wasn't anticipating much of the difficulty one has adjusting to new gear because it is, when all is said and done, not terribly different to the 500/4 I've had for years. Nor was I anticipating any problems. My experience with Canon equipment is that it is always beautifully presented and their QC people are top notch - you can count on your new lens or camera working perfectly straight out of the box.

All seemed to go well at first (other than the usual difficulty of finding interesting birds to point it at). I put it on the 7D II (which is also quite new to me, I've only had it for a month or so) and went for a drive, looking for those open grassland birds I am so fond of: pippits, Singing Bushlarks, songlarks, and so on. My usual technique with these grassland birds is to stay in the car no matter what. Even in the car they won't let you get close to them, but if you get out you are lucky to get within 50 or 100 metres.

But every now and then, for no reason I could see, the 600/4 refused to auto focus! Complete non-cooperation! Ouch! Eventually I realised (or thought I did) that the neoprene Lenscoat (not a Canon product) was at fault. The Mark II primes have a much larger manual focus ring than the Mark Is had, so the matching Lenscoat includes an extra cylinder to cover it (it was not thought necessary to cover the slim black focus ring on the Mark Is). I decided that the Lenscoat cover was slightly too long and thus fouling the focus ring such that it was too stiff for the AF motor to rotate, and therefore removed the cover.

(This was a completely stupid thing to think, as the whole point of a USM focus motor is that the manual focus ring does not rotate during AF. It's not as if I haven't known that for many years, I just had the stupids, which is strange. I mean, I had the stupids when I was young, same as I had the chicken pox. Seeing as I've already had it, I am now immune to chiicken pox. Why aren't I immune to the stupids?)

Before too long, the problem was back. Ouch! A very expensive lens, brand new, randomly not focusing at all is serious stuff. Yes, it is under warranty, but it costs hundreds to ship it (as you have to have insurance) and would be a major inconvenience. Besides, was it the lens? Or the 1.4 teleconverter? (Itself almost new.) Or the camera? Or something to do with the combination of all three?

I battled on, fiddling around, turning the camera off and on again, pointing it at object close and far, turning the manual focus ring by hand. There seemed no pattern to it. Sooner or later - sometimes after the bird had flown away - it would suddenly work perfectly. Then, two minutes or 20 minutes later, the problem would come back. I've saved up for years and years to buy this lens and it doesn't work! Not a good day.



(Evidence for the prosecution: rather blurry Richard's Pippit, manual focus at 840mm if you don't mind. Damnit, the last time I had to use manual focus on a bird it was 2004 and I was digiscoping.)


Eventually I found the problem. It was caused by the modern mania for adding useless damn live view and video functions to perfectly innocent DSLRs. I better explain.

On the back of Canon DSLRs, there is a button marked "AF-ON". Out of the box, it simply starts the auto-focus system, which is a bit pointless since a shutter half-press does that anyway. Lots of sport and wildlife shooters disable the half-shutter AF and focus only with the AF-ON button. It's called back button focus. This is a good idea because it gives you more control over when the cameras focuses and (in particular) the ability to force it to stop auto-focusing, which can be very handy. On the other hand, it makes shooting rather counter-intuitive and awkward, especially if you are hand-holding a heavy lens, and imposes a different way of shooting all the time even though you only actually need to take over control of the AF once in a while. This is why I prefer reverse back button focus where the AF ON button STOPS auto-focus instead of starting it. You can use the camera normally for everything, but when something odd crops up and you want the camera not to auto-focus, just press and hold the AF-ON button. Easy! Works like a charm. I've done it for years.

So where is my problem with the 600/4, and what has it got to do with live view and/or video?

Everything. When Canon designed the 7D II, they included that useless damn extra button immediately right of the viewfinder. It's just clutter, and a right PITA until you go into custom functions and disable it to stop the mirror clacking up and live starting every time you bump it. Now the 7D II is far from the first camera to have that extra button. From memory, even the venerable 50D had it, but on the 7D, for some reason, there is less space between that button and the AF ON button. Worse, the ridge you rest your right thumb against is much smaller and shallower than it is on (for example) my old 20D.

Result? If you have medium-large hands, when you hand-hold a 7D II with a heavy lens, you tend to depress the AF ON button without realising it. With more than 4kg of camera and lens to hold up, the tiny amount of force required to press AF ON goes unnoticed.

The cure: Mr Lens Technician Tannin went into custom controls and disabled the AF ON button: pressing it now does nothing. I reassigned the AF STOP function to the next button to the right, formerly AE lock, and haven't bothered assigning anything else to AE lock because I never use it. (When it is required, I just use more EC, or go to manual exposure. This is almost as quick and saves using up brain cells. As you can see from the tale above, I urgently need to conserve brain cells.)

Anyway, lens is now "fixed". I dare say I'll have to tweak the 5D IV in similar fashion as it has a similar design.