Wide angle lens for airshows
The 17-70mm has only SDM focussing with its KAF3 mount (screw AF drive has been omitted from these lenses)so will be manual focus only on the older bodies.
You say you want something wider than your kit lens, up to 100mm. That is longer, not wider. Please clarify.
If you are happy with the DA* 300mm, you'll love the DA* 16-50mm & 50-135mm lenses.
Peter E Smith
My flickr Photostream
Sorry for any confusuion caused...
Rob
As far as I know there is no zoom lens that goes much wider than 18mm and extends to around 100mm.
I think you are going to need two lenses (DA* 16-50 + DA* 50-135) and maybe two bodies to avoid lens changing.
Peter E Smith
My flickr Photostream
Rob
1: Either the sigma 10-20 or Pentax 12-24 for static shots. I have used the 10-20 a lot in the hangers at Duxford, more recently to take 5 auto bracketed shots for HDR use due to the high contrast lighting conditions in there
2: DA* 16-50 - possibly my least used lens at airshows, but useful for the flight line walk at Duxford.
3: DA* 50-135 - This is good for detail shots of aircraft in the hangers and formation display shots. The temptation with static shots is to try and fit the entire aircraft in, but the engineer in me enjoys focusing in on the piping and rivets for more abstract shots and the 50-135 is very good for this.
The 300mm prime will be good for most things airborne. I use the Sigma 100-300 and that never needs to come off during a display. If you have the 300mm prime and the 50-135, you have a potentially big gap, but I tend to use my 100-300 at either end most of the time and seldom in the middle.
If you want better coverage a 10-20 and 18-200 or 60-250 could possibly be another solution. EDITED because I realised I invented a lens range, doh!
Hope that helps. I am the author of the aforementioned article, but happy to answer any questions that the article does not cover or Qs about Duxford before then.
Neil
http://www.arbitrary.co.uk http://www.ephotozine.com/u25920
I find it quite useful and the IQ is not bad at all.
Would like to see some of your shots of aircraft with the DA* 300mm some time, I am undecided which long lens to buy atm.
. My Flickr

It's a model Christen Eagle II.
The model show was at Alcantarilla Air Force base here in Murcia, Spain, a few weeks ago. Some very impressive model jets flying, but I didn't use the DA* 300mm for them

To see more images of this event taken with the DA* 300mm lens, visit here. All images shot with K10D + DA*300mm, PP'd in Lightroom 2.1
The jets in formation are real aircraft collectively known as Patrulla Águila (Eagle Patrol), Spain's version of the Red Arrows.
Peter E Smith
My flickr Photostream
Kris Lockyear
It is an illusion that photos are made with the camera… they are made with the eye, heart and head. Henri Cartier-Bresson
Lots of film bodies, a couple of digital ones, too many lenses (mainly older glass) and a Horseman LE 5x4.
My website
RobE17
Member
Essex
Just some advice please re the above, in particular taking shots of aircraft in the static park as I'm looking to upgrade for next season after the wonderful summer airshows we've had this year...
I've got the kit lens 18-55 AL11 but am looking for something up to say 100mm. I borrowed the DA 18-250mm but found the range to be too big. I have considered the 17-70mm SDM but have read bad reviews about that otherwise that would be ideal. I also thought about a 28mm + lens but I would imagine that with the crop factor I wouldn't get much of a wide angle?
On another subject I purchased the DA*300mm a couple of weeks ago, used it at Old Warden and took some of my best aircraft photos ever and hope to use it at Duxford on Sunday, it is worth every penny
I did consider posting this on another forum specifically for aircraft but hardly anyone has any Pentax kit.
Looking forward to your advice and replies,
Rob