manual focus problems on k10d

I could only ever be the 16-45 to your 31 limited, George.

Just got the test chart as I've noticed some back focusing problems with my DA 50-200 and A50.

Well, all my other lenses seem to focus correctly and the camera locks perfectly.

My 50-200 seems to back focus a fair bit. Secondly, it is supposed to keep in focus thought the zoom range. Mine changes focus quite a lot as I zoom which indicates there is something wrong with the lens. It is supposed to be a fixed focus once attained thought the zoom range.

My other lenses show varying amount of minor front or back focus, normal error I'd expect from manual focus or from the autofocus. It has two contrast points it can choose to lock focus above and below the line so I'd expect some minor variation. They are generally quite consistent though.

Ok, so what next... Seem to have established it is the lens. Especially as it failed to lock focus at all at infinity out and about a couple of days ago.

https://www.pentaxuser.com/forum/viewtopic.php?t=5182

Advice, help, suggestions...

I think it needs to go back to Pentax but then I'll be without my telephoto lens

I'm not sure how accurate the design of the 50-200mm is, but lenses that should keep their focus don't always, and I would imagine the wider the zoom range the less likely focus is to hold.

A zoom technically means focus is kept spot-on as you zoom. A varifocal has to be refocused at every focal length setting. There will be a point where a cheap badly designed "zoom" is actually more of a varifocal. To be honest, I usually refocus after zooming as a matter of habit.

Lenses are not perfect in many respects, bith optical and mechanical.

It still won't lock focus correctly at infinity when set to 200mm and seems to be a bit off in other aspects of focusing.

The Pentax SMC-FA 28-200 I have needs to be substantially refocused throughout the zoom range, and ISTR someone else (was it Mannesty?) confirmed this as normal for that lens.

I guess it's just a limitation of the design of something with such a big zoom range.

In Tyr's case, I would have thought that if his 50-200 is miles different from his other lenses in terms of where it ends up being focused (for a given focal length setting), then that's grounds enough for getting a replacement. Only once it focuses correctly at all would I be inclined to worry about having to refocus after zooming.

Is it in warranty?

Is it new enough to persuade the shop to exchange it? Fit for purpose and all that...

Absolutely, take it back as soon as you can.

It is now two months old, still in warranty. Bought it online and it is a bit late to send it back now. Can still send it to Pentax for repair or replacement, but they may not do much. Is two months too long to send something back (I think it is)? Really don't want to be without it though But then again the number of shots that are off it may be worth the wait.

I think that within 28 days you might have been entitled to a replacement, the trouble with web purchases is that you can't get a human being to stretch the rules and do the exchange anyway.

But two months is not long, so I'd give it a go anyway. Write a letter putting your case, keep it polite but firm and hope for the best. It is the suppliers responsibility to sort it out in any event, at least in the UK.

If there is going to be any delay I'd be tempted to buy the Samsung one for £49.99 and get most or all of that back later on via an eBay sale.

And I believe that if it's clear that the fault has been there since purchase, it presumably wasn't fit for purpose then. Tyr seems to have been agonising about it for some time.

Not at Jacobs any more - it's £99.99 there now. Have you seen it elsewhere at £49.99, John?

No, the Jacobs offer was what I had in mind. Pity, still, even £99.99 is pretty good.

I think some of the Jessops clearance stores are or have been selling the Pentax version for around £107.00

Well, I'll email them and see what they say. If that fails then I can still have it looked at by Pentax.