I too was at the excellent Duxford Flying Legends show and was using a 55-300 and 18-135. Focus hunting with the 55-300 was an issue for me and I concluded that photographing flying planes takes practice and patience.

If you are planning to spend serious money and air shows are to be your thing, may I suggest possibly hiring the lenses on your shortlist to better gauge what you are comfortable with and what suits your working needs best as I think there is no substitute for personal experience.

One lens I can however heartily recommend for use in the hangars is the Sigma 8-16mnm.

Good look with you search...

I have the older version of the Sigma 17-70 f2.8~f4.5 and it focuses quick enough for me, plus, I think it offers more flexibility for a wedding photographer at the wide end when in a tight space such as a chapel or register office. I love mine and prefer it even to my Pentax 18-135, though some might think me a Philistine for saying that....

What lovely clarity....

Once upon a time, depth of field and hyper-focal-distance was relatively straightforward to work out. Now with the advent of digital, crop factors and lack of DoF scales on lenses, it appears to have become more complicated.

Maybe this should be sticky!

Looks like a cracking deal for any one in the market for a K5!

Good luck with your sales and I hope you enLIGHTenment on the darkside.....

AP ran an article I believe in a recent issue (week b4 last I think) on maximising depth of field. It included depth of field tables for different apertures as well as instructions for calculating DoF. Might be worth locating a copy and having a read. Other than that, check out the 'DOFMaster Depth Of Field Calculator' here:- link

This one is also well worth considering 'Vivitar 28mm f/2.8 Close Focus they come in a PKA mount link and are usually reasonably priced....

My sentiments exactly. A fantastic lens at a super price...

LCE have a used Sigma 17-70 that might be worth a look at link....

Or there is the slightly older but excellent Sigma 17-70mm F2.8-4.5 DC Macro which can probably be had for less outlay..... or even the Sigma 18-125mm F3.8-5.6 DC HSM Lens which seems reasonably priced at £229.00 by SRS link Good hunting....