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02-09-2011, 07:19 PM   #1
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sigma 24-70mm won't auto focus with pentax kx

I just got my new lens today.. I have a pentax kx body.. and the lens is a sigma 24-70 mm EX DG Macro DF Autofocus Lens for Pentax.. The lens won't auto focus! Am I missing something?? The lens is set to AF.. and so is the body of the camera.. Frustrated!

Not sure what other information to include??

thanks in advance


02-09-2011, 07:49 PM   #2
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Assuming it is clicked in properly to the mount, and the switches are all set to AF, it could be you have a DOA lens on your hands.
02-09-2011, 08:58 PM   #3
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On top of what twitch said, have you tried giving the af ring a mild twist? Don't grind it or anything, but the screws may not be engaged properly. Sometimes a nudge can get them properly connected.
02-09-2011, 11:34 PM   #4
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If your Sigma 24-70mm f2.8 EX DG MACRO is the previous version (DF=dual focus?)
and not the newer HSM version, two steps are needed to switch from MF to AF:

1) the MF/AF switch on the camera body
2) make sure the huge focus ring on the lens is engaged in the AF position

As mentionned in previous posts, perhaps a mild twist of the zoom ring while in AF
might 'wake up' a lens that has been sitting un-used for a while.
With the lens off the camera, check if the drive screw spins while doing this.

I used to own one (sold it last week!) of the older versions of this lens,
and if I understand correctly, the newer HSM version has a 'manual over-ride'
that doesn't require dis-engaging the zoom ring to MF.


Last edited by mlatour; 02-10-2011 at 03:58 PM.
02-10-2011, 08:09 AM   #5
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Original Poster
well, I am sending the lens back.. should I reorder the HSM ? the price difference is about 400$ but I want to have a nice lens so I will spend the money either way..

Thanks for your tips! Sad that none of them worked..
02-10-2011, 11:12 AM   #6
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It's a nice lens but I found it has some 'particularities...

I bought mine here on Pentax Forums from a member,
never handling one in person before, perhaps I should of done that before buying it.

I do nightime action type photography (firegrounds) what I did find with this lens is the 'ergonomics'
of it felt weird when fast zooming on shots, the zoom ring is tiny compared to
the huge focus ring and as a few owners mentionned on the forum, by design there tends to
be an hesitation/resistance moving the zoom ring just past the 24mm setting.

Also, compared to my usual Sigma 18-50mm f2.8 EX DC MACRO,
the 24-70mm had a tendency to produce more flaring in the same shooting situations.

But most of all, I realised that 24mm is just not wide enough for me,
kept it for while as a spare lens but decided to sell it just last week.

On a plus side, image quality was very good/sharp, and it's a constant f2.8

If ever Sigma made a 18-70mm f2.8 EX DC, now that would be my ideal lens!


Last edited by mlatour; 02-10-2011 at 12:51 PM.
02-10-2011, 12:12 PM   #7
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hi ashlee... i've recently bought the non macro version of this lens... using it on my k-x with no issues whatsoever.... so far, it's a pretty darn good lens.... it might be worth your time contacting sigma directly and speak with an experienced tech rep.... just might point you in the right direction... hoping of course you don't have a dead lens... but that's not too common.... best of luck, dave m - Contact Us

their phone number is in the top right hand corner of this screen...

02-11-2011, 11:43 AM   #8
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Original Poster
It was a dead lens unfortunately.. I received my new one today and it works so excite to shoot with it!

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