Thanks to everyone for your very kind advice. One lens I have thought at looking eventually at is the Tamron 70-200 f2.8 with the Pentax 1.4x converter. I wonder if that would work or if the AF would be too slow?

Thanks everyone, my interest is photographing airliners, so I think I'll give my 55-300 a go at Manchester Airport. I did use that successfully on the Vulcan farewell tour when the aircraft overflew Barnoldswick

I have both the K-5 and K-3 and am thinking of having a go at aviation photography. My longest lens is currently the SMC version of the excellent DA 55-300. Would it be wise to buy the 1.4x rear converter to use with my lens or look for something better like the DA* 60-250 f4 or the 150-450? I have to keep in mind that I'm only slightly built physically and struggled with handling a Sigma 120-400 when I tried it on another maker's body.

Hi Guys, I've recently been thinking of adding another Pentax DSLR to my collection, my current go to camera is a classic K5 which I dearly love using and I've had some nice results from. I'm looking at either a K3, which is similar in size and feel to the K5 and I also have a Samsung GX-10 which I also like using. I recently had a hands on demo with a KS2 which I liked the feel of and the weight was nice. My photography is primarily of transport and travel related subjects. Which would fellow Pentax users feel would be best for my needs, the K3 or KS2?

I upgraded from a Samsung GX-10 to a K5 and haven't looked back, the K5 is faster and offers more consistency in terms of metering. The AF is also much better on the K5 in comparison. I still have the GX-10 as a second body.

It was my first day out with the 18-135 today, and once I'd got used to the handling and the almost silent focusing, I have to say it does everything I want of it as a walkabout lens. I find it produces nice contrasty and sharp images too.

Just to update, I've bought a DA 18-135, but have yet to use it out and about, it feels nice on my K-5 and is of course weather resistant to match the body.

The sample shots taken with the Sigma look very good for a superzoom, I've had a demonstration of this lens, admittedly on a Nikon D7000 and was impressed by the feel and speed of focusing.

Two of my favourite lenses, the Sigma 10-20 and the DA 55-300 are screw drive and they are 100% reliable, I never had any issues with screw drive AF when I was shooting film with my Z-50P either other than when my old Tokina 35-300 came apart on me at Weymouth harbour. That was down to a fatigue failure of a casting inside the lens I was told. I've spotted a couple of used Tamron 18-250s with a dealer, both with 12 month guarantees, I'm tempted to take a punt even though I prefer to buy new!

It's not that with the noise John, I'm thinking along the lines of technology moving on and developments have led to smoother and quieter mechanisms in the same way I've seen them do in the world of model railways too!