@ Ed110 - very helpful and informative post, thanks for that!

I did not realise that the SDM lenses also have the screw system incorporated into the mount. It would seem logical on current and future cameras to incorporate selection of SDM or screw, and I think this would be a major selling point. Built in backup systems are never an admission of failure, they are a valuable asset (ask any pilot!) If current and future Pentax bodies DID allow the user to select screw or SDM it would immediately encourage more folks to buy the things by giving added peace of mind. At the end of the day if you have a screw drive system onboard both the lens and body anyway then it's crazy to disable the link!

Knowing the above, if I did spend a grand on an SDM lens and it ever failed I be even more annoyed!!! So the current situation is a double turn off!

Nice to hear that plenty of users here have SDM lenses that work well and don't actually have issues! What happens if they do go wrong though? Does the focus jam, or anything else stop working, or can they still be used fully functionally minus having to focus manually?

I approve of second hand shops, but I only support those that genuinely love and care for the product they sell. Anyone who shovels their stock into piles, leaves lenses laying around in dusty conditions with no lens caps over the optics, and generally operates in a pig sty clearly has no respect for what they sell. That being the case they can't have any respect for their customers either. I want to see sellers with pride, not disdain

Before blowing a load of cash for a faster system it's ALWAYS worth while checking to see if you can speed up your existing system. Often, over time, your processing speed can become seriously depleted from numerous programme updates, patches, software you may have tried loading and numerous things that can run in the background unnoticed but that you never actually need. I'm talking here about stuff like media players, system trays, instant messenger systems, quick start applications and the like. They all sit there doing nothing but eating resources, using RAM. It might be worth doing a clean re-install of windows and begin again but just add the programmes you really want, not the pointless extras. At the same time go to crucial.com and use the free scan tool to check if you're fully loaded. Doing these things can double the speed of an existing system and might save you hundreds of quid (for a new lens instead )

... and it's also an amazing lens that's worth the money. I'm very happy with mine

I have to confess to a personal policy of avoiding SDM lenses through a belief that simple is better. More complexity in engineering terms generally equates to higher failure rates and more expensive repairs, and I hate spending money on repairs that could otherwise be invested in more equipment! As an amateur I'm perfectly happy with the screw autofocus and there is a modern tendency to believe the advertising hype that new is best and old is obsolete.

Sure, if I was a pro sports or press photographer I might need SDM to keep up with the pack, but it's worth remembering too that photographers managed to take great action shots long before SDM was invented. Sometimes I think technology displaces craft.

Good advice above!

Might also be grit or a shard of something that's become lodged. Has the lens ever been bumped or dropped? Sounds like it needs to be taken apart for an internal clean and service. Time to call the pros.

Yeah, got the manual but I'm already doing what it suggests, ie using the 4-way controller. Using the right arrow just moves the cursor over the symbol selection panel above the text box, and that contains no symbol or option for a space. If there was a way of using the 4-way to move the cursor down to the text box it might help (?), but it stays up in the symbol box, which has no space option. I'm flummoxed