As people have maybe surmised, the reason for selling my 500mm f4 lens was that I had invested in something longer - an 800mm. I rarely used the 500mm without a 1.4x teleconverter, so it was a choice between 700 f5.6 and 800 f5.6. With bird photography focal length is king. 700 vs 800 may not sound like much, but it's a noticeable difference. Add to that the fact that the 800 would take the 1.4 teleconverter just as well as the 500 did, and retain autofocus with my camera, and it was a persuasive argument. The newer lens had better AF speed vs the 500 + converter, better IS, and was newer. Not that there was anything wrong with the eight year old 500mm - indeed my oldest lens dates from 1992 and operates flawlessly - but it's always nice to know that your kit is relatively fresh. The cons are half as much light, more weight (though this in fact a mere 400g), physically larger, and a longer mfd. I can get around most of these things.

- Half the light. Not ideal, but high ISO performance on the 5D3 and 1D4 are amazing. I will happily shoot at 3200 on the 5D3, and 1250 on the 1D4. This would have been unthinkable a couple of years ago. Winter, however, will be the true test.

- +400g. Any extra weight is bad, I already carry too much. But I no longer need a TC, and that reduces the difference to about 100g. I can live with that at the moment.

- MFD 6m vs 4.5m. Not great, but rarely am I too close to a bird. I have extension tubes if it ever happens. I've had the lens for two months and used an extension tube once for about half an hour on a particularly obliging Little Grebe. 

- Longer. Nothing I can do about this, and this is the biggest downside by far. The lens is difficult to pack in hand luggage, it requires a much larger bag. With various pirates like Ryanair and Flybe imposing absurd limits on hand luggage for one reason and one reason only, I face a difficult choice when travelling. 98% of my photography occurs without recourse to a plane - easy really.

The price for the 800 was right, and I felt that the 500mm would sell at a good price, probably at a peak whilst stocks of the new mk II lens continue to dribble in. This proved to be the case, and I was able to sell the 500 for considerably more than I bought it for - three years of 'free' telephoto happiness.

So, what's it like to use? My first outing was very difficult, and I wondered if I hadn't made a big mistake. My keeper rate was down hugely. Despondent, I wondered what I should do. Easy, go out again. Gradually I'm getting used to it, and the results are proving - to my jaundiced standards at least - wonderful. There is truly no substitute for focal length. I've been getting shots that just wouldn't have been possible with the 500mm. I'm no pro, but I've been getting shots with the converter, using only a monopod for support, that are blowing me away. I've yet to use it with the tripod and Wimberley, I can only imagine that the step-up in quality will be sensational. Unfortunately that's not really my style as a roving birder, but no doubt I will test it out one day. I love the freedom of a monopod, it's easily the best of both worlds, the ideal compromise. Hand-held would be useless, but a monopod is discreet, easy, light, quick and versatile. Tripods are cumbersome, slow, heavy....

So, the photos. Well, all photos recently posted have been with the 800mm. I didn't even pick up the 500mm once I bought the 800mm....and last week I handed it over to a new owner. Pangs of regret certainly, it was the lens that changed everything, but I've got a great replacement. Winter may be a different story, but I'll cross that bridge when I come to it. The new 500 mk II is still in my thoughts, especially for travel, but the focal length advantage of the 800mm is a boon.

Heron: 800mm, 1/500s at f5.6, ISO 800, monopod

Sandpiper: 800mm, 1/800s at f5.6. ISO 400, monopod

Whinchat: 1120mm, 1/1600 at f8, ISO 640, monopod