I'm sure you could always find a buyer for a quality lens.

I paid around £100 for mine around 18 months ago (no filters but mint) so I guess £149 isn't far off. This is considered the best 500mm mirror out there and is sharp. Don't forget you can try CIF with this too.

An excellent lens and not one I'm going to part with even though I rarely use it.

Fight, Wizards and Dancing are all gorgeous ! Thanks for posting the link.

Cool idea FH ! I love seeing these homemade diffusers and seeing/hearing what they can do ! I'm afraid my home-made diffuser (not used so often now as I prefer wireless/softbox off-camera) is almost identical to that of Trickletreat's on page 1.

Impressive stuff Pierro. That last shot of the young Grebe is just gorgeous.

Some excellent shots in there - looks like you had a great time with the camera !

Personally I would go for the 50-150 (used if you can find one - people tend not to sell them !) over the 50-135.

Much faster focusing (the 50-135 is infamous for it's relatively slow focus), HSM over SDM (so no fear of SDM issues), much longer guarantee (depending on where you live anywhere from 3 to 4 years over the paltry 1 year from Pentax - this is a pet peeve of mine !), sharper wide open. Do not go for the new version (with OS. Not sure if they even have a Pentax version) as it is now a beast (same size as a 70-200) and you are paying more for the same optics.

If you prefer the colours of the Pentax then set up a preset in your PP software to convert all shots as soon as you import them.

These guys weren't static (pics #1,2 & 4 were with the 50-150) :

link

... or you can see more action shots on my SmugMug : link

The 18-50 has now been replaced by a 17-50/2.8. By all accounts an excellent lens (maybe even superior to the Tamron) but considerably more expensive (but still cheaper than the *16-50) than the Tamron 17-50/2.8. The Tamron that the OP mentioned is an absolutely outstanding lens (and that's without even considering it's low price).

I'm sure you are right there Dr.

I also started macro in the same way you did because I found using flash intimidating after finding out that the undiffused on-board flash is not going to work (harsh, shadows, reflections etc.).

Dark Skies - often macro lighting set ups are not expensive at all. Mine's relatively simple (flash unit - manual is fine, stand, wireless transmitter/receiver, medium sized softbox - whatever is comfortable to work with) and if you have any flash unit at all then another 20 - 30 pounds has you covered (cheap Chinese Ebay gear works perfectly).
I also concocted one of those cardboard extending diffusers for the on-board flash which costs just a couple of pounds (or nothing if you have the bits and bobs to hand) and a little effort, they are remarkably effective.

I believe Nass is correct, in general you get more detail, more keepers. I avoided flash as long as I could but it became frustrating and I'd urge anyone just starting out to learn how to use their lens properly (as DS said) on still subjects and then quickly learn how to add and diffuse flash (or even use twin video arm LEDs which I also tried for a while but are more expensive and not as powerful as using flash but have the advantage of allowing you to clearly see and focus on the subject in poor light).