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Old Feb 24, 2012, 11:13 AM   #1
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Default AF behavior and sensor orientation

Here I am taking pictures of some bananas sitting on a fruit bowl indoors with my G3 and the Leica 25mm. As I turned the camera vertically, I noticed that depending on where the camera was pointing to, it would not lock focus. If I turned it horizontally and focused on the same exact spot, bingo...the camera locked focus instantly. I played with this over and over and got very consistent results. The camera would focus when the sensor orientation was horizontal but not when it was vertical. I switched lenses to see if it would make any difference but it did not. I noticed this behavior to be evident when contrast was not as obvious. However, I would expect the inability to focus on low contrast objects to be identical whether the camera is on a horizontal or vertical position. I have the camera set to a single, centered focus point. I also experimented with the EPL1 and could not reproduce the problem. The good news is (I think), both the G3 and the G1 behaved identically. So this is not another G3 glitch. The question is...WHY? Why would the camera behave differently when turned sideways in terms of AF? Any one?
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Old Feb 25, 2012, 7:27 AM   #2
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That's very interesting. I've been following the u43 evolution and even tho, to me, it can't compare to a dslr system, the newer models are looking much better. The symptoms you describe sound as if the u43 has no cross-point af. i can't find any info on whether they do or not. Perhaps some do, some don't.
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Old Feb 25, 2012, 9:50 AM   #3
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Your guess may very well be correct. Some older DSLR models had a center cross point and then either horizontal or vertical points. Newer models have many cross point. It will be interesting to find out as I see it as a major flaw and system draw back.
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Old Feb 26, 2012, 3:13 PM   #4
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G'day Tullio

Interesting & curious
I just got my G2 w-14-42 lens and did the same sort of thing you describe on several items on the desk in front of me and I got a 100% focus-hit

Same as your settings ...
Didn't matter whether the camera was horizontal, 30-45-60 degrees or vertical - it always locked & beeped

Dunno more than this ...
Regards, Phil
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Old Feb 27, 2012, 10:17 AM   #5
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Thanks for testing, Phil. The fact that the behavior was identical between the G1 and G3 makes me believe that the problem is not due to a defective unit. Perhaps the objects you are focusing on presents enough contrast allowing the camera to focus. I only experienced this behavior a couple of times, both when I pointed the focus point to a low contrast subject. It would be OK if the cameras could not focus at all since their AF system is contrast-based. But the fact that it focus horizontally but not vertically bugs me.
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Old Feb 27, 2012, 2:33 PM   #6
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G'day again matey

Just done another couple of tests for you [and me]
you mention above "when I pointed the focus point to a low contrast subject"

I'm in my home office, early morning, just a bit of window light, no other light on so it's 'not real bright'
Exposure is given as 1/2sec - 1/3sec x f5,6 @ ISO100

As I sweep the G2 [14-42 lens at 42]
> across the desk for white A4 papers on a white plastic box it hunted then focuses both horizontally + vertically + 45deg
> across the off-white wall towards the light switch, it hunts for a moment then beeps 'focused'
I would say it focus-locked 75% and hunted for 25%
ie- as I would expect from 'poor' light

With the Pentax Kx [18-125 lens at about 40]
> across the desk with the papers on the plastic box it also hunted till it focused both horizontally + vertically + 45deg
> across the off-white wall towards the light switch, it hunts for a moment then beeps 'focused' and got it wrong as it was out-of focus

The Kx focussing was certainly faster than the G2 but its success rate was not significally better

Regards, Phil
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Old Feb 27, 2012, 2:49 PM   #7
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Thanks, Phil. I will try a couple of different lenses and see if it makes any difference.
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Old May 27, 2012, 3:04 AM   #8
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Well, I thought you were full of BS, but I just tried this with "both" my G1's and sure enough when I hit precisely the right spot, no focus lock when vertical. Horizontal, instant lock.

I could practically put a mark on the wall where it did it. And exactly the same spot time and again. It absolutely refused to lock focus. Move just an inch or two and it's ok.

I was just being ignorant the way I was testing because I didn't really believe you. Then it just did it. "STRANGE". And "both" the G1's did it in exactly the same spot.

I'm not even sure I'd call it low contrast. I used an unlit room (it's 4:00 AM here), with a wood grain wall and a beige/tan drapes at a picture window. It's right where the darker wall and the drapes meet that it does it. I took a shot in black and white and it's very obvious the different shades and clearly defined.

It didn't hunt at all, it focus locked instantly or not. No hesitation, just no lock.

This is weird. In the black and white mode, I can see that spot clearly. I can point the camera exactly at that spot and it won't focus. Move just slightly and it will.

That's a new one on me.
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Old May 27, 2012, 11:11 AM   #9
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Well, I guess I was not full of BS after all. In my case, the problem occurred indoors in the dining area during the day and my house is full of light...we have more windows (and huge ones) than walls). I was photographing some bananas in a fruit bowl. As you also experienced, move the camera slightly and the focus is locked. However, only when the camera is positioned vertically the camera can't lock focus. Turn it horizontally and it locks instantly. As I also mentioned, it happens with both the G1 and G3.
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Old May 29, 2012, 1:04 AM   #10
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Tullio,

I repeated those tests again and again last night. Same conditions and results. I finally was able to find that mark so precisely that I could change to spot focus and target that mark. When I did that, I could get the same lack of focus in vertical or horizontal. It did seem harder to hit horizontally and was in a slightly different location than it appeared vertically, but once I found it, it happened again and again.

It must be contrast. In the dark room at night, it looks like a black line along the curtain to wall, but in the daylight I had to get close and look to see where the curtain ended and the wall began. That must be what the camera is seeing.

Now, I think that has happened to me before with some outdoor shots. I just didn't recognize it. And I think it's happened with my FZ28 also.

Anyway, I'm glad you mentioned it. At least I'll know what it is that I'm trying to work around it if it happens again.
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