It does hunt on a K-5! I had one of those mated to the Sigma all weekend, while the 17-70 was glued to a loaned K-7 (part of SRS's wonderful customer service when your other K-5 has camera flu).

Focus speed is fine, but sometimes it tends to hunt with brisk-moving objects (and ends up locking on the wrong area). At quick corners - the chicane in #6, for instance - I usually pre-focus on a set point, switch to MF and keep my fingers crossed...

Good luck finding a Sigma 100-300mm f4. They come up on eBay occasionally, but only occasionally.

Wider-angle shots taken with K-7 and Pentax 17-70mm f4, close-ups with K-5 and Sigma 100-300mm f4.

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/Alonso1-40.jpg[/IMG] 1

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[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/PdlR1-4.jpg[/IMG] 7

Thanks to all for the gracious comments. Kirsty, the pan/movement shots were taken with a K-7 and Pentax 17-70mm f4. The light was a pain, changing from bright to shade every few seconds, so I tended to use shutter or aperture priority rather than manual settings. Those posted here were all taken using shutter priority (and hand-held).

#1 (Audi pit stop): 1/10, ISO400 (camera selected f10)
#2 (MX-5): 1/20, ISO100 (camera opted for f9)
#6 (Aston): 1/80, ISO200 (camera pitched in with f6.3)
#7: (Porsche at night): 1/25, ISO3200 (camera struggled, but grudgingly allowed f4)

My default panning preference is 1/100 or 1/125, but that fluctuates according to car performance and cornering speed. At the 'Ring this weekend, the first corner was very tight and slow so 1/20 or 1/25 worked for a few shots. If I'm panning an F1 car at 200mph, there's not much point venturing below 1/200 (although that doesn't stop me trying and then spending 20 minutes pressing the 'delete' button).

Not very scientific, I'm afraid, but I hope it helps. Generally, I think the recommendation is to start at about 1/250 to practise technique and then work your way down. Good luck - and enjoy Rallye Deutschland.

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All taken with K-5 and Sigma 100-300mm f4

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[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/Senna2-10.jpg[/IMG] 7

Likewise. Often see them when I don't have my camera to hand - or when it's fitted with a short lens - but I have yet to take a decent green woodpecker snap. Nicely done.

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[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/Wild752Watts772.jpg[/IMG] 7

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I witnessed a skirmish in 2006 - the main highway blocked by piles of blazing tyres, during one of the frequent Friday evening exchanges - but mentioned it only in passing, in one of the specialist magazines. As you say, such stuff went largely unreported. So far I haven't seen any trouble this year, although I know it has been creating headlines in Europe.

As for security, we have the customary circuit patrols - provided by the usual Austrian company - with extra local padding. During yesterday morning's routine bag check, I mentioned to a bored Austrian that the prohibition signs mentioned nothing about guns. "That's right," he said. "You can bring those in, so long as you don't have bottles of water or drumsticks..."

I have known less quirky race weekends.