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02-14-2016, 04:14 PM   #1
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K3 vs k30 autofocus on Da35mm Macro (and Da70mm)

Anybody got any opinion on how the k3 compares with the k30 on autofocus accuracy using the Da35mm macro and Da70mm wide open?

Basically, I think the k3 I got in December has an autofocus problem. There's a couple of threads on the forum which talk about K3s with inconsistent autofocus and I fear mine maybe one. Unfortunately, it's not as clear cut as the autofocus simply not working. Generally, it appears that my k3 is ok when you stopper the lens down and increase DOF, but opening up the Da35mm macro to f2.8 the autofocus misses a lot. It also seems to be inconsistent opening the Da70 up too, but I've spent most time with the Da35 and I haven't really used my k3 with other fast lenses.

Generally, I'm finding that the non centre focus points aren't too bad when no fine adjustment is set to the lens, but the centre points tend to back focus. If I try and correct the centre point with fine adjustment it knocks the non centre points out of focus (at f2.8). But even worse, I seem to get it set for the centre point, and feel like I can use it, but later I notice it's missing again and it needs a different fine adjustment value. I really don't feel I can trust the k3 to focus at f2.8. I've spent a lot of time messing with the fine adjustment trying to get it right, but generally not getting anywhere.

It also seems that sometimes you can dial it in so it seems like it does ok on one focus distance but fails at focusing on something at a different distance.

There's a lot of variables involved, I've had a go with a calibration chart and feel like I've set the numbers right, but then taken it out in a real world situation and it just tends to be all over the place. In these situations if I swap the lens to my k30 the autofocus is much more reliable, rarely missing focus at f2.8.

Any advice? Am I likely to be doing something silly? Is there known issues with k3/Da35 macro combo?

I'm really frustrated, as I love all the other aspects of the k3, but not being to trust it to autofocus reliably at f2.8 is a deal breaker. I know PDAF is never going to be perfect, but if it was performing like my k30 I'd be happy.

I did buy the camera used (online store) and they do a 12 month warranty on used equipment, so if I've just got a bad copy I hopefully could do something about it. Unfortunately, as it's an inconsistency at fairly fast apertures, rather than a clear failure, I fear I may struggle to convince them there is an issue.

02-14-2016, 05:33 PM   #2
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I had trouble focusing with my da70 today with a k 50 lots of back focus, so I had to go manual focus for some shots.
02-14-2016, 07:08 PM - 2 Likes   #3
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interestingly I've been some what suspicious of my K30 auto focus & fine adjustment of late, having originally tuned in my DA55-300 and been very happy with the results, I downloaded a lens auto focus aid, (target & sloping scale type) and set about to fine tune all my lenses, I've got to say It wasn't as clear cut as I would have thought, and after readjusting the fine AF adjustment on my DA55-300 the setting was quite different, and real world shots proved a little disappointing. I retested & adjusted again with a similar result, so I checked using some toy figures and confirmed it was back focusing about a 1-1.5 cm which can make all the difference trying to get the eyes tack sharp in bird shots. So I adjusted using 3D figures rather than the test target, - a happy camper again. Your situation & focal lengths are different I know, but my point is I think real world "3D" adjustment can be different to flat test targets. IMO.
02-14-2016, 08:35 PM   #4
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You're better using CDAF from live view for critical focusing.

On my K-50, although the DA 70 is OK at infinity,
short-range focusing with PDAF is not good enough at f/2.4.

Here's more food for thought:
http://www.lensrentals.com/blog/2010/07/how-autofocus-often-works

02-15-2016, 03:21 AM   #5
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Possibly.. But my k30 is pretty reliable with both these lenses, apart from the odd PDAF miss... But the k3 is all over the place.

I'm more convinced it's an issue with my copy of the k3; I'm hoping it is and the shop fixes it then I'll be extremely happy . With no fine adjustment on the k3 the centre points significantly back focus at close distance, but seems ok at near infinity. The outer points are the opposite: Not bad at close distance but severely front focuses at near infinity. My k30 has no such issues, it's good at all distance (within what you'd expect from PDAF) both centre point and outer points behave similar (with a bit of a higher miss rate for the outer points).
02-18-2016, 03:54 AM   #6
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Sounds like something is wrong indeed. Stop making yourself crazy and send it in for AF calibration
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