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06-02-2011, 08:16 PM   #1
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Just did AF Fine Adjustment - all my lenses are off?!

I took a bunc of macro close-up pictures of a bumble bee earlier today using my D FA 50 mm macro. When I reviewed them they were ALL out of focus - focus point appeared behind the bee (back focus?). I had read about this AF adjustment, so since I apparently had a problem, I started searching.

I found some instructions for doing focus adjustments at FocusTestChart.com. First I tried various adjustments and nothing changed: Discovered you have to turn off the camera and/or take off the lens. After doing both the changes took and I finally settled on a +7 adjustment to my macro lens. I then checked my other lenses. A 16-45mm, a 55-300mm and a 18-55mm WR. They all appear to need a +2 or +3 adjustment. Seems I can do a +2 for ALL, and override with +7 for my macro lens.

Here is my first question: Is this fairly normal? I have had the camera for about 5 weeks, and did think there were quite a few pictures that were softer than I had hoped - but always figured it was just me...

Second question: Following the instructions, I was taking pictures of a test chart just a few feet away. Can I expect the same adjustments to work when the subject is much further away?

Any other guidance you can give me?

06-02-2011, 08:50 PM   #2
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QuoteOriginally posted by HenrikDK Quote
Here is my first question: Is this fairly normal? I have had the camera for about 5 weeks, and did think there were quite a few pictures that were softer than I had hoped - but always figured it was just me...
BF/FF is not uncommon with DSLRs of any brand. It's how tight the manufacturing QC is. However, OOF doesn't automatically mean BF or FF. Pentax DSLRs have wide area AF sensors which might cover more than you think. They tend to be attracted to higher contrast target regardless of distance. That means if the background has higher contrast than the intended target, it will AF on the background. Sadly unlike some Nikon DSLRs, there is no option to alter this behavour (like forcing it to pick the closer target) so you just have to know how it behaves and work around it.

QuoteOriginally posted by HenrikDK Quote
Second question: Following the instructions, I was taking pictures of a test chart just a few feet away. Can I expect the same adjustments to work when the subject is much further away?
I have calibrated my own Pentax DSLRs and from what I have learnt, calibrating AF based on printed chart is flawed because the shooting distance is too close. A simple explanation is that turning the focus ring 1mm near infinity will have far greater impact on focus than near 0.3m. I suggest fine tuning the AF based on daylight target at least a few metres away. Also, AF is inconsistent even when properly calibrated so make sure to repeat the tests many times and obtain an average result. When the camera/lens nails the distant target well, it should be fine for closeup.
06-02-2011, 08:50 PM   #3
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Normal for me.
I have a global +7 adjustment.
All are sharp as a tack now.
Results will be exaggerated with a focusing chart due to thinner depth of field, so focusing errors will be more noticeable in closer subjects. Far away subjects should have no changes to focusing accuracy.
06-02-2011, 08:59 PM   #4
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Those charts work great as long as the focus point is aligned exactly to the 0 point on the target. Sort of hard at 45 degrees. Remember too that the focus point is actually a focus zone and that correct focus is determined by edge contrast. A more conclusive check would be using a target parallel to the sensor plane. I would suggest using one of the moire pattern targets. These are highly sensitive to even small inaccuracies in focus. Unfortunately doing a test with that type of target works best if you have a focus rail with a scale, but it might be worth the trouble if you want absolute calibration.

A couple of other things to be aware of:
  • Most AF systems have at least some variability depending on light source (tungsten vs. daylight vs. shade vs. fluorescent...)
  • Macro with AF is pretty hit or miss, especially at higher magnification approaching 1:1. The issue is not the AF system. Rather it is DOF and the difficulty in actually detecting the intended focus point and adjusting the lens to that point. We are talking a few millimeters DOF even at f/8.
  • AF for any subject with a receding surface (say a model's face in oblique view) with a wide aperture (f/2.8 or wider) is also unpredictable for the same reasons that macro is hard
And finally...the camera doesn't have a clue what your intended focus point is.


Steve

06-02-2011, 09:24 PM   #5
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Most of my lenses required AF calibration with both of my K-5sand adjustment wasn't consistent between K-5s

focus charts, I have discovered, are of limited use and the best way is to take a whole load of real world pics at your most open aperture and set AF calibration to give you the best performance
06-02-2011, 09:34 PM   #6
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Thanks for all the advice.

For the macro shots earlier today, I was using center focus, so I thought I knew what I was focusing on, and still it was way off. Hopefully the adjustments made today will provide improved results.

I will do some more more testing to see if further away focus is Ok or maybe even better. I don't really understand the difference between testing close in or further out, though? It seems just relative difference...

Finally the test pattern I was using seemed very easy to focus on, and the results were very consistent with multiple pictures. With my slower lens it was a question of using +2 or +3, but both of these were clearly better then the default zero setting.
06-02-2011, 11:22 PM   #7
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only my da * 55mm required af adjustment everything else was either slow enough or good enough to be acceptable that i never tested properly. the 55 being f1.4 requires more precise calibration and ended up at +8.

What was interesting was that focus charts showed +6 but real world use needed more.
06-03-2011, 01:33 AM   #8
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I've had the K5 a couple of weeks and having checked the lenses have found that no adjustments are needed

Simon

06-03-2011, 01:40 AM   #9
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I have about 30% of my lenses needing fine adjustment.
I'd think it depends on the camera and lens matching.
06-03-2011, 06:05 PM   #10
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I hope this isn't too obvious

But I didn't see you mention whether or not your K-5 had the latest firmware installed ver 1.03. The last release took care of many problems for many people. I'm guessing everyone has assumed or already knew you had the most uptodate firmware so I hope I'm not being too obvious but it never hurts to check.
06-04-2011, 06:19 PM   #11
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QuoteOriginally posted by geezer52 Quote
But I didn't see you mention whether or not your K-5 had the latest firmware installed ver 1.03. The last release took care of many problems for many people. I'm guessing everyone has assumed or already knew you had the most uptodate firmware so I hope I'm not being too obvious but it never hurts to check.
The 1.03 update was supposed to help fix the front focussing in low light.

.... however it would make a lot of sense to recalibrate your lenses in normal light levels following an update to 1.03

Last edited by Smeggypants; 06-04-2011 at 06:30 PM.
06-04-2011, 07:38 PM   #12
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does the k-5 calibrate for all lenses or can individual lenses be saved?
06-04-2011, 07:54 PM   #13
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QuoteOriginally posted by figmental1978 Quote
can individual lenses be saved?
Up to 20 individual lens calibration settings can be saved.
06-04-2011, 08:15 PM   #14
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^ awesome, cheers.
06-04-2011, 10:08 PM   #15
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And does the camera know what lens is mounted automatically?
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