I've been to a couple of motorsport events this year - Wimbledon bangers and a single-venue stage rally at Brands Hatch, basically - but it feels as though the campaign is gaining added impetus in the slipstream of a busy mid-week test session at Mallory Park. Busy for bikes, at any rate...

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/bike55-1.jpg[/IMG]1 Sigma 105mm f2.8 macro

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/sidecar3-3.jpg[/IMG]2 Sigma 150-500mm f5-6.3

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/Viper1.jpg[/IMG]3 Pentax DA 17-70mm f4

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/bike20.jpg[/IMG]4 Sigma 150-500mm f5-6.3

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/Grindrodpick-up3.jpg[/IMG]5 Sigma 150-500mm f5-6.3

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/sidecar14.jpg[/IMG]6 Sigma 150-500mm f5-6.3

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/bike50-2.jpg[/IMG]7 Sigma 150-500mm f5-6.3

Compliments to both judge and podium nominees. Now if you'll excuse me, I'm off to work out vignette methodology in PS Elements...

I can't make a comparative analysis between the K-5 and anything with a Nikon badge, but in response to the original question about the K-5's suitability for motorsport...
[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/Rosberg1.jpg[/IMG]
Korea, with Sigma 150-500mm f5-6.3


[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/White1-1.jpg[/IMG]
Brands Hatch, with Tamron 90mm f2.8 macro (not an obvious choice, perhaps, but using the 100-300mm meant standing in nettles and I was wearing shorts)...


[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/bike19-1.jpg[/IMG]
Mallory Park, with Sigma 100-300mm f4


[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/Trulli4r.jpg[/IMG]
Monza, with Tamron 70-300mm f4-5.6 (focusing manually, because the lens isn't really fast enough to track F1 cars)


[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/PriorAriel2-1.jpg[/IMG]
Cholmondeley, with Sigma 100-300mm f4


[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/JdA2.jpg[/IMG]
Suzuka, with Sigma 150-500mm f5-6.3


[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/L1011.jpg[/IMG]
Brands Hatch, with Sigma 100-300mm f4

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20wildlife/robin1-5.jpg[/IMG]
Robin belts out his siren mating call from behind some foreground bokeh.

Taken on Feb 19 in Kelsey Park, Beckenham, UK.

K-5 & Sigma 150-500mm f5-6.3
1/250s, hand-held
f8
ISO 800
440mm

Michael, at the risk of being an accessory to hijack, the Sigmas work perfectly well with aeroplanes and racing cars etc (see sample images on the first page of this thread). I guess it depends how quickly your kids run or swim!

The 150-500 is only f5-6.3, so you might be better sticking with the 50-150 f2.8 for indoor use, if the light is tricky. I haven't tried a 60-250 f4, but have seen them used at motorsport events.

Bizarrely, given my previous comments in this thread, I took the Sigma 150-500mm for a walk this morning and it briefly displayed some of the non-contact symptoms hitherto exhibited by the 100-300mm. Only briefly, mind, and most of the shots were OK. I then took the 100-300mm for a stroll and it was generally reliable. Samples below...

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20wildlife/fox7.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20wildlife/mandarin1-3.jpg[/IMG]

The 150-500 has been fine to date, but then I've only owned it since August. It came with a three-year warranty, too.

Yep, same symptoms. Happened with a K-7 and K20D as well as the K-5. It has been back to Sigma and serviced elsewhere, but the problem usually returns within a few months. PMs welcome if anybody knows a tame Sigma engineer who does a good job for a fair price. I really would like to get it sorted.

Apologies for veering OT.

One or t'other. The 100-300 (a used purchase) has been a bit troublesome, which is why I bought the 150-500 when SRS lowered the price. I love the 100-300 when it works, but wish it would do so more consistently. For European races, it's usually a matter of which lens can most easily be taken on board without EasyJet noticing...

A few motorsport samples taken with the Sigma 150-500, from the second half of 2011...
[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/Hamilton5-1.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/RaweAH100M1.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/Schuey3-7.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/ElySlaterBetts2-1.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20club%20motorsport/Williamsetal1-1.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/Trulli1-15.jpg[/IMG]

[IMG]http://i396.photobucket.com/albums/pp41/simonarron/Simon%20Arron%20-%20F1/Schuey4-5.jpg[/IMG]