I would expect so. I have a A400 F5.6, and it's quite a bit better than my Sigma mirror lens, especially stopped down a bit.

It's also quite a lot better than a (non APO) Sigma A400 F5.6 that I also have, if that helps any.

It's big and heavy though.

A thing of beauty, certainly, but if you're after something lightweight that you can hand-hold all day, you might consider a workout programme first.

Can you be a bit more specific? Where, when? Exactly what problems are you experiencing?

Typically it might be difficulty achieving sharpness and/or detail, and/or getting the exposure right against a bright sky.

Not quite sure what you mean by "flight line" - typically the aircraft orient themselves with respect to the runway in use, with which the front of the crowd is usually parallel. And of course the aircraft are always above that.

Of course, distance is key. Getting up really early and being right at the front is a major benefit. And of course there are limitations of having 300mm as the maximum focal length at your disposal.

As Mike says, the K10D isn't ideal, but with determination, it can produce good results.

I use it with the Pentax DA 55-300, and occasionally get some decent enough shots.

Ah, I see. I understand what your'e getting at now.

Well in that case, you may as well get the 18-55 kit lens. F4 rather than F2.8 isn't all that much of a difference most of the time, and the high-ISO performance is so good that you probably won't need that extra stop.

If you need to take pictures when the ambient light is that low, you'd be better off putting the money towards a flash gun, or a tripod

Er, Ok. I have no real idea what you're talking about, I'm afraid, but good luck with your K-5 anyway.

I do rather suspect that "it's a lens for a beginner" is a phrase that only a beginner would use.

By the way...

Checking the spec of the Canon G9, it appears that (ignoring the 4:3 sensor size), its zoom range gives an angle of view equivalent on 35mm to 35-210.

On the K5, a zoom range of about 23-140 will give you a comparable angle of view.

The OP may want to bear this in mind, if he hasn't already, when thinking about the zoom range he's interested in.

With the greatest of respect, you've been using a bridge camera, and you've never owned an SLR.

To say that F4 'is out', and talk about 'sacrificing IQ' seems to be a little premature

Yes, you may sacrifice a little IQ with the 18-135 compared with the star lenses, but for most practical purposes the sacrifice is small.

And your desire to stick with 'budget' lenses is in any case at odds with getting the very best possible IQ.

If you want budget lenses, the 18-55 and 55-300 are probably your best bet, and as has been said, together cost less than the 18-135.

I wouldn't disagree with this.

The thing is, the OP is coming from a bridge camera with a substantial zoom range, so having only the 18-55 may feel like a retrograde step in that sense only, although of course there will be many other advantages.

So I still think that the 18-135 will be the single most useful one to get for now.

All this talk of FA50 and DA16-50, excellent though they are, is missing the point a little, I think.

For a beginner, coming from a bridge, all the benefits of a decent zoom range as well as the K-5 makes it a no-brainer for me, subject to funds available.

The 18-135 will also hold its value very well, so it's not as if there aren't plenty of options later on.

I have three lenses, covering the range 10-300, and I'd still love an 18-135 as a walkaround lens.

I take George's point about the 12-24 being good for buildings, but overall, I'd vote for the 18-135 with its extra reach.

You have to be very careful at close range with extreme wide angles, especially with people near the edges of the frame.

And given how the 18-250 was good, considering its ludicrous zoom range, I'd hope that the 18-135 would be better throughout its whole focal length range.

After all this time, it's still the 18-55 (with the 55-300 a close second) that's on my K10D the most, and I expect if I had the 18-135 it would be that instead - especially on the K-5 with its high ISO performance.

Yes, I've had a similar experience.

Have a look at my post here, and in particular at the 'before and after' shots.

I don't use the blower any more, except on lenses, for exactly this reason - it makes things worse as often as it improves things.

As I said in my earlier post, you'll probably need a wet clean.

Bite the bullet, get the swabs and fluid (RTFM so that you get the right materials), do it yourself.

It's very easy. Barely harder than the butterfly, in fact.

For sticky particles, a wet clean will almost certainly be needed.

Not only will the Arctic Butterfly not work for anything that is actually stuck, but it may smear what's there, and also contaminate the bristles with crap.

This will reduce its effectiveness for things it is good at, namely dust that is not adhered, and which therefore can be removed just by electrostatic attraction.

Sometimes it's hard to tell what sort of muck you have. It's just tough.. as the Visible Dust FAQ says:

[quote="visibledust.com"]
How can I tell if the contamination is dust or a stain?

Dust particles will come in many shapes and sizes such as specks and fibers. Stains will usually look fairly round and uniform, and sometimes cast a distinctive halo around the edges. Sometimes it is hard to differentiate between the two so the best course of action is to perform a dry cleaning. Best case scenario: clean, then you are finished. Worst case scenario: a smear is caused, a wet cleaning will need to be performed, followed by another dry cleaning (followed by cleaning your bristles).[/quote]