Also gives 'depth is field preview' as it stops the lens down!

Lots of good advice above about the Pentax fish-eye and the fact it distorts (nicely for some shots) at the 10mm end. I have the Samsung version and wouldn't part with it but the fishy distortion doesn't suite every wide shot.

Have you considered the Sigma 8-16mm?
I had the old Sigma 10-20 f4-5.6 (not the current f3.5 HSM version) but changed to the 8-16mm. It is definitely a better lens all round. The extra 2 mm makes quite a difference and it is sharp.
Rumored to be discontinued but SRS are still advertising it on their website at £449.

I'd be happy to buy 2.

I agree the DA18-135 is worth a look. It's my lens of choice for tramping in the mountains. Light, compact and fast focusing. The DC motor seems to be robust, never heard of anyone having problems with the autofocus drive. Nice lens for landscape use with a very good range that means I won't need to change lenses all day. Even with WR there are times when you don't want to be opening the front of your sealed camera!

The DA16-85 is also a good lens. It is sharper than the 18-135 but it is also bigger and heavier. It also has a DC autofocus motor. This is the lens I use when I'm not going to be carrying it up and down a mountain all day but am not going out to do 'photography'.

The 50-135 is the bees knees in terms of image quality but it is a big lens and it would seem the SDM motors have a certain fragility. (Mine is waiting to be repaired at the moment). I think you might find it a bit heavy on the bike.

My gallery has plenty of mountain pics taken with the 18-135 some more recent non mountain ones with the 16-85.

If you remember, we tried not changing the clocks a few years ago. Then the government decided to start doing it again.
Doesn't matter what happens really, there will always someone telling us their way is better and the arguments will happen every year!

Personally, I agree with you. There is no sense in changing the clock but It does seem that we are in a minority.

Marmite sarnies are supposed to be another midgie repellent. Before you ask, you eat it!

Watch you don't get DEET on plastics, Some of them get dissolved by the stuff. We had a brand new tent groundsheet ruined by my wife spilling some. The polyurethane proofing just became porous,

Hat with midge net. Gloves, that you can operate the camera when wearing. Best defence is to not let the midge's near your skin or go in the winter. Wind is also useful for keeping the midge away but unfortunately it often comes with rain.

Best view of a mountain is often from a smaller one nearby. The view from the top of the mountain doesn't include the mountain your on!
Torridon is great. Views across the loch and from surrounding hills/coast.

4kg sounds like a lot to me but maybe your fit!

Only problem is that the old lens probably isn't weatherproof!

Further improvement can be made with the notebook and one of those pencils with a rubber on the end.
Gives you full word processing capabilities!

Seriously, If you want to make note taking quicker, just draw on some columns with iso, fstop, shutter speed or what ever else you want to record.
You could also use the EXIF info, for the camera settings, that are already recorded with the image as you take it. Saves having to make notes at the time.

And that's just from the K, M and A series and a small selection of the cameras.

Thing is, LBA doesn't have to be expensive with Pentax. Loads of K mount lenses by lots of manufacturers out there. If you have an M42 adapter there are even more potential lenses to try.