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12-14-2007, 01:34 PM   #16
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QuoteOriginally posted by jeffkrol Quote
for a couple of reasons 1) are you saying that there is no sharp point of focus at 50? ie: cannot manually focus at 50 to be sharper and have to zoom /focus/ un-zoom to get a sharp image?
2) since the AF "zone" has a much larger area at 50 then 135 then naturally AF "errors" could arise due to AF on things that are not planer.. ie much farther and or closer all in the same frame of AF reference?. I assume you were attempting to focus on the post w/ the address, which at 50mm is considerably smaller then at 135..... and the AF area could include things in the foregroud/background.
Personally it is a "good technique" to maximise the AF area of interest and then back zoom.
And a good thing that the lens "holds" as I believe some would not. If you back zoom the optics change enough to lose AF........
EDIT: You seemed to have cleared up one point, the 50 has no focus at all at least according to your last post.. That's not a good thing and frankly would be hard to explain since the lens groups should be the same if natively at 50 or backed off to 50....
No, no, I can manually focus the lens just fine to infinity

I was just talking of this particular pictures (and some others of the same kind) where I can't exactly see where the focus is.

It is effectively good technique to zoom in to focus but had some suprisingly oof pics @50mm where I could not find what would have fooled the camera.

I am not used to that with the K10, I have actually found the AF to be really precise so far, thus my interogations.

12-14-2007, 03:22 PM   #17
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QuoteOriginally posted by jeffkrol Quote
2) since the AF "zone" has a much larger area at 50 then 135 then naturally AF "errors" could arise due to AF on things that are not planer.. ie much farther and or closer all in the same frame of AF reference?. I assume you were attempting to focus on the post w/ the address, which at 50mm is considerably smaller then at 135..... and the AF area could include things in the foregroud/background.
Looking at the photos, I was thinking the same thing.

Lol, perhaps you can try the test with a high contrast subject that does not have anything directly in front or behind the focus point.
12-14-2007, 05:24 PM   #18
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QuoteOriginally posted by rogerstg Quote
Looking at the photos, I was thinking the same thing.

Lol, perhaps you can try the test with a high contrast subject that does not have anything directly in front or behind the focus point.
Yes, I'll try that but in this particular picture, the zoomed and reframed shot is sharper all across the frame (from the closer trees to the far away details), not just where I wanted it to focus.

If the AF was fooled by some other details, they must have been past infinity (and beyond...)
12-14-2007, 07:57 PM   #19
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just did a quick short range, indoor, low-light test (it's dark by now here) with my K10+ DA 50-200 and the results were inconclusive. I'll have to test it tomorrow when the sun is out.

12-15-2007, 02:27 AM   #20
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Here is the test at infinity.
The effect is more clearly visible.
I still think that this is normal (for Pentax AF at least), since when the AF has a larger base to measure, the result will be more accurate. At least it is what I experience with other zooms as well.

When you look at the distance scale, I note that at 50 mm it is focussing slightly beyond infinity! That would explain why you cannot find a sharp zone at all.
Perhaps firmware yould be improved that focussing beyond infinity is blocked.

Conclusion: Not a lens problem, but a general AF problem.

12-15-2007, 04:34 AM   #21
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QuoteOriginally posted by blende8 Quote
Here is the test at infinity.
The effect is more clearly visible.
I still think that this is normal (for Pentax AF at least), since when the AF has a larger base to measure, the result will be more accurate. At least it is what I experience with other zooms as well.

When you look at the distance scale, I note that at 50 mm it is focussing slightly beyond infinity! That would explain why you cannot find a sharp zone at all.
Perhaps firmware yould be improved that focussing beyond infinity is blocked.

Conclusion: Not a lens problem, but a general AF problem.
Yes, I did further testing this morning and came to the same conclusions.

1/ It is apparent mostly (but not only) at infinity where the lens focuses past infinity (I looked at the distance ring and it goes past the mark);

2/Even at infinity it does not always do that, I have had about 30% misfocused shots n my tests this morning (bright sunlight).

I agree, it doesn't seem to be a lens issue (I don't have other zooms to test it with: sold almost everything to get the DA* ).

I am going out for a brief test of my 50 and 12-24.... see y'all!!

Last edited by lol101; 12-15-2007 at 05:01 AM.
12-15-2007, 05:16 AM   #22
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I did a test with the 12-24 and now, it will often hit the infinity mark rather loudly (as if willing to go past it but it cannot turn past the mark, contrary to the DA*) and refuse to lock (blinking AF light in VF).

This has never happened before I upgraded to v1.3 so I am now leaning toward a firmware issue.

I also tried the FA 50 and it seems to work fine.
01-07-2008, 07:41 AM   #23
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I have a 50-135 that seems to be doing this as well at 50mm. mine occurs when focusing on objects closer than infinity as well. It does focus fine if i zoom in to 135, focus lock and zoom back out to take the photograph. I did a quick test with my kit lens and it also does not focus too well at the wide end, zooming in and focusing produces a more accurate focus. I wonder if it a camera issue as well.

01-07-2008, 08:33 AM   #24
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QuoteOriginally posted by qksilver Quote
I have a 50-135 that seems to be doing this as well at 50mm. mine occurs when focusing on objects closer than infinity as well. It does focus fine if i zoom in to 135, focus lock and zoom back out to take the photograph. I did a quick test with my kit lens and it also does not focus too well at the wide end, zooming in and focusing produces a more accurate focus. I wonder if it a camera issue as well.
Hi,

it seems to be the case with almost all zooms of all makes, it's apparently normal...
01-07-2008, 08:17 PM   #25
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lol101, what AF point are you using? AUTO, SEL, OR SPOT?
01-08-2008, 03:57 AM   #26
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QuoteOriginally posted by ramshot Quote
lol101, what AF point are you using? AUTO, SEL, OR SPOT?
Spot or SEL usually.
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