I used to buy a lot of lenses, then I added the D800 to my K5 and sold the majority of them deciding instead that quality over quantity was far more important.

On the K5 I think the DA*300 has not only the IQ I'm looking for but it is a very versatile lens; birding, sports, portraits and landscape detail.

On the D800 (and of course these can be bought for Pentax, hence why I'm mentioning it here) the Zeiss ZF 2 35/2 isn't their most expensive by a long way, but it's absolutely stunning in sharpness, rendition and colour and other than my birding lenses it is hardly ever off that camera.

Steam Mill St for me - an interesting and different shot.

Sorry Smeggy - can't agree with you on this one. A blurry photo of a bird is of no use whatsoever. The first rule of bird shooting is get the shutter speed up to where you need it to avoid unwanted blur. Also a shallow DoF is often anathema to bird shots when most often you want the whole bird (or as much as you can) in focus. When using a 300-500mm lens the low DoF comes naturally anyway ! I love low DoF shots but it is often a secondary or tertiary target.

When I can get it : 1/1250 - F8 - ISO 100 is perfect (though the shutter speed may need to be higher for faster winged birds depending on whether you want wing blur or not, and can be lower for large birds) though most of the time that is compromised by the light so I'll widen the aperture first, bring the SS down to 1/640 - 1/800 and let the ISO ride to 6,400 if I absolutely must.

Early mornings often see 1/500 - F4.5 - ISO 2,000 - 3,200 though !

Another very nice set Alan - I do love these birds !

People are going a little OTT on the DA*300 I feel. I have and love this lens but unless conditions are near identical it is difficult to judge.

In this case better light (blue not grey skies !), a larger aperture and faster shutter speeds are going to make a big difference to sharpness, colour and clarity, especially so when hand-holding big lenses such as the 150-500. Though the DA*300 is of course still a better lens overall !

The point made about the focusing speed of the DA*300 vs the Sigma 150-500 just seems to bear out the test that that European magazine made, Pentax cameras & lenses target accuracy over speed. I've found this to be true of the Nikon/Sigma 500mm too, much faster but not always as accurate.

Alan - here's an example. Not my work, someone offered to give it a try. My original and his reworked blue sky version.

No question considering your uses : K5 (new if you can get one, used if you can't).

EDIT : Oops too late. Hope you enjoy your K30.

Really good shots Alan. Whilst you are inundated I haven't seen one this year (we do have them) !

#1 does indeed look like a dinosaur sized bird eating an orange !

I see your grey skies do detract a little from the shots - someone was trying to teach me how to change grey to blue the other day (I don't have PS though and it's tough to do in Aperture). A useful skill to learn perhaps

Firstly nice shots ! The DA*300 is one of my favourite Pentax lenses.

Wet weather - get yourself a weather jacket for whatever non-WR lenses you use, cheap and they work, Pros at football matches still have to get their shots !

I was hired as part of a 4 man (and woman) team for the Shanghai Sevens last month (I also shot it last year). Last year I used the Sigma 50-150/2.8 and DA*300 (with and without the AFA x1.7, mostly with) and it worked out just fine, all AF systems will miss some shots, your settings are just as, if not more, important (f5.6 or mostly f8, TAv and preferably 1/500 - 1/1250).
This year I used the D800 & Sigma 500mm with the K5 and 50-150mm and it was the perfect set-up (for me). Forget about crop factor (since with the resolution of the D800 you can virtually crop as deep as you want to go).

I'd recommend a similar set-up on the K5, a 50-150 (if you can find one) as the AF is significantly faster than the 50-135 and a 500mm (the AFA works great on the DA*300 since you are using it at longer distances it is always at infinity and the AF is virtually instantaneous) for when the players are on the opposite side or end of the pitch.

That may well indeed be the case in some instances however there is a lot of empirical evidence to the contrary (I'm assuming the metal in the filters is softer or lower quality).
To use a (poor) analogy, seat belts save lives, but perversely they are also the cause of some car crash deaths.

It's not just the front element, there are a number of cases where the thread has been so damaged by the filter that it becomes non-viable after the broken filter has been removed.

Front elements, especially in modern lenses, are as tough as nails and really don't need the 'protection' of a weak glass filter.

As I said pros and cons and we must each balance the odds and choose our own path.