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10-08-2009, 10:13 PM   #1
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Join Date: Oct 2009
Posts: 1
K100D can't recognise lenses - pls help?

Hi All,

I'm a newbie & new to the forum as well. I've had my Pentax K100D for over 2 years now originally with Pentax 18-55 kit lens & later acquired Sigma 10-20 Ultra Wide & Sigma 30mm prime.
My firmware is 1.02, I use NiMH rechargables (generic brand).
Have previously tried M42 lenses with adapter & set the "F1 with S lens used" & "Using aperture ring" setting to available in Custom settings.

I've used both Sigma's without issues until recently, when my K100D started acting strange.
The issue is that the camera does'nt seem to recognise the lens when I switched between the lenses and is exacerbated as it is intermittent.

So when I change lens, with SR on.
1) camera powers on but the SR will ask what focal length the lens is at (even though it always recognises the lens previously)
2) The camera shows Aperture as F--
3) As my Sigma's does not have an Aperture ring, I can't control the lens even if I have it on manual focus.
4) The only metering mode available to me is "center-weighted" & "spot", whereas the previous "Multi-Segment" mode that used to be there, is now missing.
5) Even with the above conditions, the 18-55 kit lens continue to work! ie has auto-focus, reports aperture etc but NOT the Sigma's, no autofocus, no aperture reading.

I've taken the Sigma's back to the shop where I bought it and they've tried it on other Pentax (not K100D, no longer selling) like K-M, K-7 etc & the lens works.
So I've taken the K100D to a repair shop and they've had a look at it. All the guy did was rub some alcolhol solution on the electrical contact points and "luckily/or unluckily" the Sigma lenses work again.
So I thought, aha, just needs some cleaning but when I got home, and changed lenses, it started happening again.
When testing & changing lens the problem becomes intermittent with 1 time out of 20 times, the camera righted itself (ie the Sigma lens work again) but more often than not, the above problem persists.

I was tearing my hair out and spent hours searching the internet but I can't seem to find anything. Have tried to clear all settings by resetting the camera, issue remains.
I just don't know why the camera behaves this way although auto-focus/aperture readings always work with the kit lens but the Sigma's work only intermittently.

One thing I did notice between the kit-lens and my Sigma's is one of the parts "moved" in the Sigma when I twist the focusing ring whereas the Kit lens are stationary (does not move).

That part (which I believe controls the auto-focus) is highlighted in red circle below.

On my kit lens this part does not move when I twist the focusing ring.

But on both my Sigma's this part moves when I twist the focusing ring.

Does anyone ever have this problem? Or can point me to relevent sources on the internet?
Any help much appreciated.

Thanks :-)

10-09-2009, 02:30 AM   #2
Senior Member

Join Date: Sep 2006
Location: Tartu, Estonia
Posts: 159
Pentax has quick-shift focus

that means: focusing ring is decoupled from AF-drive for manual adjustment if needed- very neat and offered only on SDM lenses by other manufacturers. Your Sigmas behave like FA or FAJ (the lattest have no aperture ring either) lenses from Pentax- direct coupling from AF drive to focusing ring.
Maybe You can give a try and inspect the contacts carefully (maybe some of them have had some deformation- sitting deeper etc.) and clean them again (I personally use soft eraser for this).
Best and happy shooting, JR

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