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Old Dec 17, 2006, 7:32 AM   #1
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Hello,
while playing with my new *ist DL2 with the kit lenses I got the feeling that the AF wasn't "on point", so I did a test today. I placed the printed user manual on a table and took some photos. AF is spot, ISO 200 - so it should be pin-sharp to my mind. What I found is that the AF point seems to be closer towards the camera than where I am aiming at.

Example pic:


I was aiming at the word "pentax" in the center of the pic, which is the one from "www.pentax.fr". But the most sharp area is below (more towards the camera), Af seems to be 2-3 lines below?!

I did several shots and got the same result with different camera settings. EXIF data on pic is intact - you can see for yourself - at 1/1500s there is no camera shake playing tricks on me.

I can't imagine what I did wrong - there's no camera adjustment I could have set wrong, I just attached the lens to the body and fired away.

Please say your opinion - to me this looks like a serious problem! Is this coming from the camera or from the lenses? Did you had such a thing for yourself in the past too?

Manual focus works - but the "AF hint" the camera gives me (sound, symbol) comes at a setting which I don't consider "sharp".

:?:?:?

Thanks in advance,
Th.
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Old Dec 17, 2006, 7:45 AM   #2
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Is your Diopter set correctly? That will cause things to looks oof in the vf when manually focusing, but as for your camera focusing 3 lines below where you aim... I have no idea.

_____


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Old Dec 17, 2006, 8:00 AM   #3
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Hi,

What lens and was the lens set to infinity by any chance?



rudy
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Old Dec 17, 2006, 8:41 AM   #4
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out of my 5 lenses only one is AF, so I don't know much about that. but you may have front focus problem. and as I have split screen in my DL2 when my camera focuses it's not in focus on split screen and I don't know what is the cause. the photos are sharp when using AF lens or manual lens. this problem is most obvious when shooting close ups with shallow DOF, but for that you are better with MF anyway.

anyway: to check if it really bothers you do some test shots, but not like this one, try shooting portraits, or architecture or landscape. if you happy with results don't worry, if photos are really out of focus try replacing your camera.

I tried your test and mine DL2 lokos similar, maybe a bit better. focus is one line higher than yours.

greg
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Old Dec 17, 2006, 8:52 AM   #5
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If it is faulty then it's commonly called FF or front focusing, the reverse being BF or back focusing. All DSLRs are prone to this problem, it's purely a matter of internal mechanical adjustment.

However, it's easy to be misled by these sort of tests. The dioptre setting can fool your perception of the true 'in focus' point during MF adjustments as your eyes can be slightly misfocused to compensate small errors. Also, with AF, the red marker in the viewfinder may not be exactly the point of focus, i.e. it can be larger than the red mark or slightly offset from it, so if the test subject is a sloping surface a front/back error is the result. On my K100D, the area that can capture an AF lock in centre focus mode is more like the size of the middle circle, so you have to be careful with these sort of FF tests.
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Old Dec 17, 2006, 9:28 AM   #6
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Thanks for the fast replies, will answer your questions before I have to leave for some hours:

- I use the Pentax 18-55 kit lens
- Diopter is as I got it from pentax - works ok with my glasses
- @bluwing: what do you mean with "set to infinity"?
- @gfurm - was shooting the others (landscape, portraits) and this was when I got the feeling something is wrong
- I will add more test pics to show the problem later, short breakdown:

When you look through the viewfinder, there is a circle in the middle, which is not closed. When I set my target at the line between the lower ends of the circle (roughly) the camera focusses correctly.

This is holding it horizontally.

Holding it vertically in the same environment produces a much better (if not to say pin sharp) focus.

@SteveB - ah! I am relieved this is just mechanics so this can be adjusted. Nothing wrong with that for me - that's life.

@All
Will post another set of photos so you can help me to confirm it's FF and thus I can exactly describe my problem to the seller/Pentax.

/wave
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Old Dec 17, 2006, 9:52 AM   #7
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do THIS

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Old Dec 17, 2006, 12:56 PM   #8
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Hi Th,

One more factor to consider is the color temp of the light. Tugsten has been shown to sometimes throw focus tests off. You also want a reasonably strong light source to give the system good contrast to work with. Work with a tripod and fixed target for absolute accuracy. Try it in natural sunlight as well -- and do a number of refocus/shoot cycles. AF isn't foolproof, and some small variations in focus point is normal. If misfocusing is consistent (in terms of BF, FF and degree), with every lens, then there might be a problem that you might want to get fixed.

Scott
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Old Dec 17, 2006, 1:01 PM   #9
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if you are brave and need to make an adj.
try
THIS

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Old Dec 17, 2006, 3:25 PM   #10
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Do you know that I just love the internet in these moments when you got a problem and know some people from all over the world that are there to help you?



I did as the PDF said - more or less. I didn't checked for exactly 45 degrees - but everything else should be ok.

Here are the results:

#1 - horizontal


My POV: the text "This text should be perfectly in focus" is on the very border of the area I personally would consider "in focus" (this is showing some good will, to be honest). It's ok on the 2mm mark and it starts to show a hint of blur on the 14mm mark, but between these two it's ok. Focus sit's somewhere between the 6mm and 10mm mark I'd say.

#2 - vertical


My POV: this looks much better. It shows a very slight tendency to FF (compare the two 10mm marks for example, or the upper 6mm: it shows a sign of blur already), focus sits somewhere between the lower 2mm and 6mm mark.

EXIF is intact - I cropped, resized and applied a minimal USM to fight the resize blur.

So - should I call the seller and send in these pics and ask to fix? I doubt this can be considered to be normal, or?

Thanks again for the help!

Yours,
Th.
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