Apologies. Missed the 50-135, and that it works ok.

The suggestion about enough power is a good one to follow, but I note also that the 16-50 '...worked at first...', which suggests something has changed. Different batteries perhaps?

Don't miss what Archie said about cleaning the contacts just inside the camera mount.

Also, look at lens fit. Is the lens lose or tight when mounted compared to the 50-135? Maybe it's just not making proper electrical contact. I've seen solutions to similar problems where the lens is rotated back a little once mounted to ensure contacts are properly aligned.

The lens with the problem is the only one with SDM. The K-x would use SDM if available. It can't 'fall back' to screw drive.

The fact that the lens works on a K-5 would point to the problem being with the K-x.

Clean the contacts on the K-x camera body; try again.

That'll be a graduated ND filter, but they come in different types - hard and soft grad - different strengths, ie 1 stop, 2 stop, etc, and sizes. They also come in different systems - Cokin, Kood...Lee - which normally are reflected in price vs quality. More you pay, the better the quality of the filter itself, ie lack (or reduction) in colour cast, resistance to scratching, versatility, etc.

There's a lot of good advice on this forum, and in books. Research first and know exactly what you want, or you could be disappointed and broke!

Although you've had a few replies already, it would help if you said why you want filters. Exposure, effects, what?

Also, what equipment are you using? Could be what you're looking for is built in already.

The more information you can give, the better the advice you'll receive

Household insurance? Mine covers personal possessions away from home.

Also, here's someone who had a similar problem;

http://forum.mflenses.com/pentax-p30t-broken-advance-lever-t29255.html

Just in case you need it, service manual here;

http://pentax-manuals.com/manuals/service/p30_service.pdf

Password is 'Pentax' - note high case 'P'.

Can't remember which - Benvie, Noton or Hoddinott - but one of these guys uses battery 'studio' kit for field photography. Might be worth researching?

If I can I'll scan through my various books and see if I can find the references/kit.

Anyone got/seen one of these?

http://www.amazon.co.uk/AmazonBasics-Backpack-Cameras-accessories-Frustration-Fr...=sr_1_7?s=electronics&ie=UTF8&qid=1308175138&sr=1-7

Seems a good deal, if only for storage!

Be careful. Bought some cheap NDs - HUGE colour cast. Great if you like purple: