I've had both the 170-500mm and the 50-500mm. As a recommendation, I wouldn't go with the former and get the Bigma if you can afford it. They're both heavy lenses and the relative difference between the two in weight isn't worth the consideration in choosing one over the other. With the examples I tried and had, the Bigma was far superior to the other. I don't have any experience of the new Sigma lenses which replace these two which are both now discontinued.

I no longer have either lens.

The main downside to the Bigma (apart from the weight which you do get used to after a while) is that you do need very good light using it at the long end with the minimum f/6.3 (f/6.7 as it reports on Pentax). The view through the viewfinder can also be a bit dark, making focus judgement tricky.

I'd recommend, at a minimum, a tall sturdy monopod with ball head to help with stability.

Bear in mind that the newer replacements both use HSM, which is a bonus, however neither sport the EX moniker, whatever that substantially means.

Personally, I'd be tempted to go with the Pentax DA* 300mm (which I have) and zoom/crop. You're probably going to get a sharper image doing this compared to the equivalent size shot from the Bigma, plus you get weather sealing, a brighter VF and a couple of stops extra light.

Someone posted a mini-review with pictures of the flash (the Pentax version) over on pentaxforums.com - certainly look good, but I'm *still* holding out on the Pentax one which was meant to turn up last month

I just got back my K20D just 7 days after taking it into repair at Pentax HQ in Slough and I owe them a big Thank You.

Just over a week ago I dropped my Pentax K20D attached to my Sigma 500mm f/4.5 from a height of around 1.5m onto a hard wooden surface

The K20D suffered a smashed ViewFinder and Pentax performed a repair and service on the camera within 7 days including the time for return via courier - fantastic service!

Thankfully, the Sigma lens appears to have come through unscathed. Perhaps because of the Lenscoat protection that I added to it.

I was lucky, things could have been (financially) much worse.

Such service and professional communication with Pentax certainly inspires brand loyalty for me.

Someone has it over on pentaxforums.com and it does look good, but I'm holding out for the Pentax one.

Nowhere it seems

Pentax UK page:
http://www.pentax.co.uk/en/photo.html

PDF file for the claim:
http://www.pentax.co.uk/en/getDCMSFile.php?uid=fae9788ea19cef9919a273ca5f77b59a

Shame the 60-250mm isn't listed.

IANAL, but this wording:
probably means that since no money has changed hands, there's no contract yet, so they can change the price. That said, it wouldn't be very good business practice to go around stiffing customers.

Adobe is trying to make DNG the standard RAW format with an eye to software compatibility in the future. Support seems to come quicker for DNG that PEF support in some software and if compatibility is a concern in the future, then DNG might look more promising than staying with the proprietary PEF. DNG is generally not compressed (though they can be). Image wise, there's no difference - or at least there should be no difference.

DNG files for the K20D aren't compressed and are ~24MB. You can always shoot in PEF, which is compressed and probably save up to 50% depending on the photos.

I use the D-range setting at ISO200 for Macro shots with flash and have been finding it very useful. It helps preserve details that I can pull out in PP and because the lens is so sharp at macro distances the additional noise seems better controlled. When I've used d-range with more general wildlife shots I've found that, although it can help preserve highlights, it simply adds too much noise and can easily ruin shots.