Sigma 50-500 focusing

For the first few weeks after I got the Bigma, I was astounded at how well it focused on the K-5, even in very dim light.

Tried it again last night, it was awful - hunted like crazy and wouldn't lock at all. Tried again in bright daylight this morning, it wasn't much better.

Tried it on the K10D, it seemed fine. Put it back on the K-5, it was fine again. Now it's rubbish again.

I'm minded of this thread, since the symptoms seem superficially similar.

So, those that have the 50-500, especially the HSM one, how low does the light level have to be, before it won't focus reliably any more?

The lens is well within warranty, but I thought I'd float the issue here in case anyone can shed any light.

Like you I was and still am amazed how quickly the Sigma can focus but, there are occasions when the camera/lens just doesnt seem to see and focus on what I want it to. Problem is the image in the viewfinder is by then a total blurr both for me and I presume the focusing processor. This has happened on near, distant, high and low contrast subjects.
Usualy when I test it again not in anger it works OK, but it is annoying me as I have lost some good action bird shots due to the problem.
When trying to get birds in flight I have overcome this by using constant focus and auto focus area. This quickly locks focus on, but I'm still trying to get really sharp images using this method.
I will keep persiting with it and if I can shed more light on my problem I will post again.
Regards David Robinson
PS
dcweather has added a similar comment to a gallery photo see link
https://www.pentaxuser.com/photo/user-14131/hawk-38944

Still getting these intermittent focusing problems with the Bigma

... now, I have a memory, or at least I imagine that I do... that there was a thread on here a few months back that discussed something similar.

I may be completely making this up, but if there's something that will stop me having to send it back...

Can anyone remember a post about something simple that someone managed to do, that cured AF problems with one of the big Sigma zooms?

(I've tried searching, both here and on Google, but no joy).

Had my Bigma since 2008 has worked perfectly until last week. I used it Saturday on a walk with no problem, then went out on the Gower coast on Sunday and it would not autofocus, just kept hunting. Then it stopped working altogether and I got an F showing in my screen on my K10D been dead ever since tried other lenses on body and all working perfectly. its never been dropped, got wet or left in the car to overheat.

as it is way out of warranty will it be cost effective to send it to Sigma UK or should I just bin it and upgrade? mine was old APO model not DG.

LINK Tarrif 7

Should cost you no more than that for Sigma to fix it, the lens repaired has got to be worth more so at the very worst get it fixed and then sell it.

Thanks Mike-p

Will be working in London next month so will drop it in for repair.

Dave

give Alan Marlow a shout he has been very well recommended on this site by various members, he sorted out my FA50 very quickly and at reasonable cost. here is a link to his web site

http://www.cam-rep.co.uk/