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02-03-2012, 01:51 AM   #16
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update: putting the k-x in autofocus continuous seems to improve things a lot. going for some more test shots ...

02-03-2012, 10:38 AM   #17
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QuoteOriginally posted by DownhillGR Quote
marc i don't quite understand what you are saying. those where a few representative shots of about 1200 shots taken at a trip. i use the tamron which by the way is a much inferior lens, for more than 3 years and now i have to start to learn to be more carefull.
The fact that you happen to seem to have agreed with the camera's chocie of focus more often with the Tamron than with the 35 is probably a combination of coincidence combined with now seeing what you expect to see because one or two failures have mistakenly "taught" you to expect the 35 to not be good. Yes, having to be careful with focus is mot unique to the 35 - it's true of all lenses, and more true when shooting at the larger apertures offered by faster lenses (since DOF is shallower). It's as with many things - we don't notice a problem that has been around for a long time, but as soon as the problem happens to get noticed, we start seeing it everywhere. You see this, for example, every time a new disease is reported on the news and suddenly clinics are filled with people calling on reporting the symptoms.

So, while I know it can seem at first like there is a problem, sometimes it takes another set of eyes and or someone with braoder experience to see what is really going. Perform a series of controlled tests and you'll see these perceived differences disappear in an instant, I assure you.
02-04-2012, 06:25 AM   #18
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marc that's an orthological way to see it and believe me i tried. that's why i'm posting here, trying to keep the lens cause i like it. Anyhow for me it's a big inconvinience to have to send the lens back to england and wait for a new one... The autofocus continuous mode didn't make a big difference

Just a long shot: does anybody has any idea if i can reduce, in K-x debug mode, the size of the center autofocus region?
02-05-2012, 12:35 AM   #19
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The focus sensors are defined by the hardware; there is no way to alter them.

02-05-2012, 07:47 AM   #20
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searching about my problem i came among other links to this one which demonstrates a problem very similar to mine.

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/138605-back-focus-problem.html

So, what's the bottom line? Are we going to accept as a fact that pentax has a crappy center focus point and there's nothing we can do? This doesn't make any sense! Pentax offers many large aperture lens! I can't accept the fact that pentax uses a sensor that can't perform acceptable at large apertures and then sells cheap large aperture lenses! How can somebody overcome this "large center focus sensor" problem?

what others do to counteract this problem?

Last edited by DownhillGR; 02-05-2012 at 07:53 AM.
02-05-2012, 07:50 AM   #21
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also if this was true shouldn't manual lenses expose the same problem? I have a manual 50 f2. I usually use it with the "catch in focus" function and most of the time gives me decent focused shots.
02-05-2012, 09:24 PM   #22
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Like I said, hard as it may be to accept, I see *no evidence whatsoever* there is any problem here. You recently discovered that focus sensors are larger than you previously thought, and now you are seeing the problem everywhere, but it is no bigger of a problem now than it was before in reality. you have simply become more sensitive to it now, and have come to associate it with with your DA35, which is coloring your judgement. I know you don't want to believe this, but it is quite obviously the truth to an objective outside observer.
02-05-2012, 11:09 PM   #23
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QuoteOriginally posted by DownhillGR Quote
So, what's the bottom line? Are we going to accept as a fact that pentax has a crappy center focus point and there's nothing we can do? This doesn't make any sense! Pentax offers many large aperture lens! I can't accept the fact that pentax uses a sensor that can't perform acceptable at large apertures and then sells cheap large aperture lenses! How can somebody overcome this "large center focus sensor" problem?

what others do to counteract this problem?
If nothing else, the right side sharper than left side ice skating picture seems to show a decentered lens. That's worth more tests and perhaps a report to your seller or Pentax.

I frequently have trouble shooting at night with all of my autofocus lenses. You'd think picking the center AF point and focusing on a headlight or bright spot in the distance would work, but it fails me sometimes. After the second or third try, it's time to switch to manual focus and just get on with it. I've been burned by the unexpectedly large AF sensor issue before in all three of my Pentax DSLRs. It's frustrating, but yeah, you have to accept it and either adjust your technique or hope another company gets it right for you. Autofocus systems are incredibly complex and sensitive; while I'd happy accept world-class performance, I also can't afford to pay for it.

My solution to AF problems is to not let them get under my skin, keep working on my manual focus skills, and hope Pentax keeps improving things with each camera.

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