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02-13-2015, 11:09 PM   #1
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Pentax K-30 + Sigma 120-400 DG APO OS HSM AF problem

Just went to a local camera store to test this lens out since the store is having a clearance sale on this lens in Pentax mount.


I mounted the lens on the camera as usual, turned on the camera, and the AF moves from infinity to closest focus distance then back and the focus is not focusing on the point (I use 1 point center point focus) and there's no AF confirmation beep.


But when I mount my 18-135 kit lens everything is fine again. Focuses quickly on spot with confirmation beep sound.


Anybody have this similar experience? Is it the lens or camera or both that's not communicating with each other?


The sales representative said they will hold the lens for me and they will check with the local distributor of Sigma to see if a lens firmware update is required for it to work on a K-30. He that said they have similar experience on these third party lenses which is quite annoying but there's nothing they could do other than asking both the lens company and the camera company about this issue.
They've even helped me to update my camera firmware to the latest 1.06 version but still didn't help. The weird thing however, is that they've tried the same lens on a demo K-S1 and everything works fine. Not sure if it's my K-30's part causing the issue. They have tried 2 copies and both have same issue.


Any ideas?


Thanks!

02-14-2015, 04:43 AM   #2
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Could it be too dark in the camera store to achieve focus? I would find that pretty strange, especially since the K-30 does pretty well in low light. Another thing could be dirty contacts, Have you cleaned the contacts on the mount? They could be lined up slightly different than your lens. Just curious, what's their price on the lens?
02-14-2015, 06:51 AM   #3
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Yeah, poor light could be the issue. That's a big lens and not a particularly fast one. My 150-500 needs a fairly bright subject but it does acquire focus indoors, not that I will ever use it inside. Check your contacts and the next time, try aiming at the brightest area of the store. Also, make sure you have enough room and are within the minimum focus distance.
02-14-2015, 08:27 AM   #4
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Thanks both for the reply. I agree brightness and distance might be a problem. I tried focusing on a camera inside a display window which has display lights on it but maybe it's still a little too dark. A black subject such as a DSLR camera might also be an issue? I'll go there tomorrow and try again focusing on the brightest areas with a distance and see. I'll clean my K-30's contacts beforehand as well.

The lens is selling at approximately $575 USD. I have no experience with the lens prior today but based on the user reviews here and my experience with a friend's Bigma 50-500 OS, I thought the 120-400 OS shouldn't be that far off compared to the Bigma? And the price is very affordable for me. There isn't many 400mm to choose from for Pentax mount after all, not to mention a stabilized 400mm.
The Bigma is btw so good. Well my friend is using a D3s so probably that helps as well, but I tried it at dark night with only street lights and decorations (at Christmas time) and the focus is still bang on and fast! The OS is insanely good as well I have no problem taking sharp photos of Christmas decorations with it at night.
Disadvantage is that the Bigma Pentax mount is more then double the price of this 120-400 OS, and it's also bigger and heavier. I still haven't actually tried the 120-400 today due to this focus issue or else I would have been able to tell the 120-400 OS's performance. But physically, i'm happy with it. It's smaller and lighter than the Bigma I can at least foresee myself hand holding the lens with the K-30 for a period of time without an issue, plus it fits in my Lowepro Fastpack 350 in which the Bigma doesn't, so that's huge.

Well I'll keep my fingers crossed and have a second try tomorrow before awaiting for some news from Sigma on Monday (hopefully). I'll keep this thread updated in case anyone is also interested in the lens.

Any ideas on this issue however is greatly appreciated, it'll help a lot in solving this problem for me and other fellow Pentaxians who are interested. Thanks!

02-17-2015, 12:47 AM   #5
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Just went to the shop to try it again yesterday. Focusing at the brightest spots in the shop, I was able to get a focus confirmation beep. But I would say it's 1-2 out of 10 times that it would be able to get a focus confirmation, the other 8-9 times the lens AF just move to min focus and back to infinity. But even the sales said this shouldn't happen as even smart phone or simple point and shoot DC camera would be able to get a focus. Hence there must be something wrong with either the camera or lens or both. He said to update me when they've got any news from Sigma.

They also said that these stocks are early old stocks and are perhaps with the earliest/oldest firmware, so perhaps Sigma has a newer firmware for this lens which could solve this issue.

Hopefully that's the case, fingers crossed.
02-17-2015, 09:10 PM   #6
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Actually, my iPhone is f/2.2 and many P&S cameras are f/2.8 and even faster so you can't compare a telephoto which is f/4.5 on the short end and f/5.6 on the long end. Those cameras also use a completely different focus system.
02-27-2015, 10:06 PM   #7
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Just stumbled upon this while comparing the K-30 and K-m on specs. I realize that the K-30 has KAF2 lens mount while K-m supports KAF3, KAF2, and KAF. Is this the reason why the 120-400 have compatibility issues on the K-30 because it has an HSM motor on the lens that requires KAF3 to work?
02-27-2015, 10:16 PM   #8
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I just got a firmware update on the non-OS version of the Sigma 120-400 to enable CDAF autofocus (live view). PDAF (through the viewfinder) worked fine before the update though.

Your camera may need the latest firmware also.

02-27-2015, 10:47 PM   #9
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QuoteOriginally posted by vonBaloney Quote
I just got a firmware update on the non-OS version of the Sigma 120-400 to enable CDAF autofocus (live view). PDAF (through the viewfinder) worked fine before the update though.

Your camera may need the latest firmware also.
Interesting, my K-30 has version 1.06 I think it's the latest firmware? Will ask Sigma to update the firmware of the lens and try it out again.
Btw, I just tried one of my friend's Sigma 70-200/2.8 Macro II HSM lens and it works perfectly on my K-30. Even in indoor dim light it focused pretty quickly. The F2.8 helped a lot as well I guess. So the HSM shouldn't be the problem I guess?
02-28-2015, 08:28 AM   #10
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QuoteOriginally posted by cleffa Quote
Interesting, my K-30 has version 1.06 I think it's the latest firmware? Will ask Sigma to update the firmware of the lens and try it out again.
Btw, I just tried one of my friend's Sigma 70-200/2.8 Macro II HSM lens and it works perfectly on my K-30. Even in indoor dim light it focused pretty quickly. The F2.8 helped a lot as well I guess. So the HSM shouldn't be the problem I guess?
I know some (third-party) lenses definitely needed an update to work with CDAF. And I think some cameras needed an update for the some of the Pentax lenses (and the Pentax 1.4x TC) to work properly with CDAF. I have not heard of anything not working with PDAF because of a firmware issue, but your Sigma has the built-in OS also so that may complicate it. But if there is an update from Sigma, I'd definitely get it. You just have to pay the shipping to get it there and turnaround time is only a day or two.
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