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02-13-2012, 12:07 PM - 1 Like   #1
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AF microadjust on K-5

Yesterday I was covering an event with my K20D & DA*50-135 and the K-5 with DA*16-50. Bare flashes and Flashwaves. Vivitars 285hv's.
My plan was to have the k-5 as main camera and the k20 for headshots. ISO used 320-500. This allowed me to keep a minimum of F4 and a shutter speed of 1/60.
Ambient lighting was with FL's on a pretty low level, the 285's managed to give me a good color balance.

I knew already that my 16-50 is not on the same level with the 50-135, but hoped that the K-5 will manage to even the odds a bit with the low light capability
However I had a huge surprise from the K20 and the 50-135. The quality of light overpowered the relative lower light capability of the k20. The sharpness was over the roof even @ ISO 800.
On contrast the K-5 was almost a deception. The pictures looked like P&S compared to the K20. Not enough detail; as if there was a lot of NR involved. Checked that, NR OFF.
OK, let's switch lenses. Now with the K-5 with the 50-135 should be a killer combo. Well, not quite. Still lame.

Luckily, most of the important shots required the longer focal, so the K20 got the 50-135 back. But the issue was bugging me on the back of my mind. WTH? I had awesome results on my K-5 before.

Today I started checking the K-5 autofocus. I downloaded charts, printed a few versions but I wasn't getting satisfied. In my experience a perfect adjustment made on close range & max aperture doesn't guarantee good results in real life situations. Anyway...

DA*50-135 required initially a -2.
Huge disappointment from my FA 77. +20 didn't seemed enough. At this point I started thinking I must be doing something wrong.
Anyway, the adjustments didn't seem to make enough difference. I was feeling beaten.
Looking in the menu I saw on the microadjustment "off" description it was mentioned "Lenses will focus according to factory default tolerances".
So, I turned it off.

I am now getting perfectly focused results with all my AF lenses. More important: Perfect real life results. Even the 16-50 shines.
I got back my shiny perfect sharp camera, but...

How can this be? Could it be that the correction is built in the lens? I cannot explain it in a different way.
Can anyone confirm this, please?

Octav

02-13-2012, 02:26 PM   #2
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I think that off is simply off - I guess the message is trying to say is lenses will focus according to the tolerance of that particular lens, i.e. if the lens is at the extreme of it's tolerance it may be off with a camera with a mid or additive tolerance - I see what they mean but am struggling to explain it myself - just simply off is far easier to understand.
I also think you hit the nail on the head when you say "In my experience a perfect adjustment made on close range & max aperture doesn't guarantee good results in real life situations"
02-13-2012, 02:37 PM   #3
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Interesting...I think I'll give it a try on my K-5, mainly because I had enabled AF fine adjustment almost immediately
after I bought it. Since then, there have been a few firmware upgrades, but never thought of testing my lenses
with the AF fine adjustment turned off for the latest iteration.
It might turn out to be a goose chase for me, but it can't hurt.
02-14-2012, 04:57 PM   #4
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I did... and have.... I turned mine off after downloading latest software and far superior results.
Having said that.... I also turned off SR which I kind of had a habbit of leaving on.
This also caused a lot of out of focus pics.
It also crossed my mind if it was feasable, that, once a lens has been calibrated on camera does it stay that way when turned off !
Its certainly strange indeed !

02-14-2012, 07:29 PM   #5
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Yes... there were a few posts before discussing about turning off the AF adjustment option and everything seem to work well. I have since turned that off and it seemed to work with every lens (DA*, FA limited... etc.). At first, I thought if I left the option on, but keep the adjustment at 'zero' should be the same, but it is apparently not the same effect.
02-16-2012, 06:48 AM   #6
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Original Poster
This is great news. Let me rant about it:

Probably when the micro-adjust is off, the camera defaults to factory adjustments (camera & lens). This is logical since only a small number of users will perform micro-adjustments. Custom is OFF
When the setting is on, micro-adjustments default to 0 (regardless of the factory calibration). Then the user has to find the values himself.

SO: Micro-adjustments OFF could mean: camera +2, lens +9. We always presumed OFF = 0.

Else said, if my rant is OFF not necessarily = 0.

Octav
02-16-2012, 07:57 AM   #7
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QuoteOriginally posted by octavmandru Quote
This is great news. Let me rant about it:

Probably when the micro-adjust is off, the camera defaults to factory adjustments (camera & lens). This is logical since only a small number of users will perform micro-adjustments. Custom is OFF
When the setting is on, micro-adjustments default to 0 (regardless of the factory calibration). Then the user has to find the values himself.

SO: Micro-adjustments OFF could mean: camera +2, lens +9. We always presumed OFF = 0.

Else said, if my rant is OFF not necessarily = 0.

Octav
I took quite some time figuring out the fine adjustment and have to say that a) it works and b) it is really difficult to judge best focus even on well defined targets. So, what kind of target did you use to optimize depth of field? Besides the adjustment be aware that the AF is not always spot on! I can see 30% outliers (wrong focus) shots in the +/-10 range for the K5. Shooting from a tripod, ... The same effect happens in real life, a little bit of movement make things look in or out of focus.
A new fine adjustment calibration is on my to do list for the next week(s). Viewfinder shimming will be next.
02-16-2012, 11:14 AM   #8
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I used the Jeffrey Friedl's Blog chart.
And no, the AF micro-adjust is not gimmicky. I'm sure in some cases is a great tool.

My point is: Normally we don't need it. Normally we should keep it OFF.
As another poster said a while ago, we are not paid to do calibration work for Pentax.

When I attempted the calibration, I printed the 5% version to be sure the camera wasn't focusing near the target.
I was getting constant backfocus with the FA77. While adjusting, I could see the clear area moving towards the target.
When I disabled the micro adjust, I got constantly perfect focused images with all my lenses.

Come to think about it, it is working in a logical way for the people who do calibration as a day job. The implementation looks poor to me, because it's not user friendly or intuitive.

02-16-2012, 11:44 AM   #9
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LensRentals.com - "This lens is soft" and other myths

But with my K-5 I tend to get the feeling that Pentax PDAF is random at best. Sometimes spot on, sometimes nowhere even close. Perhaps it has to do with the low light color temperature like it was thought earlier, perhaps the relatively large AF area like some suspect, perhaps the position of the moon.
02-16-2012, 12:07 PM   #10
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Interesting discussion. time for my own rant

Recently been shooting some play rehearsals on a stage; those shots have been coming out sharp consistently. Infrequently have been shooting some headshots of actors; those shots have been disappointingly soft at times - arrgh.

This work is primarily with K5 and Tamron 28-75. My prep ahead of time is to take shots at home of some signs placed on my refrigerator with magnets. I try to adjust focus at about 8 to 10 feet away to simulate real world conditions. And its working successfully for my stage shots.

Didn't occur to me till now that i could have taken those headshots with liveview. In the discussion of mirrorless cams, occasionally see the comment, "why would anyone want to buy one". My Answer: Because i'm tired of playing around w/ focus charts - i just want to take pics.

Anyway, the ops point is worth trying. I'll see if it helps. Some folks have mentioned that lenses may focus differently at close distances than far distances, and turning off the in-camera microfocus may provide an optimum focus at all distances. Or there may be focus adjustment data in the lens chip that helps the camera. Wish we had more info from optical technicians that actually do this kind of work - may help clarify the discussion.

End of rant!
02-16-2012, 12:19 PM   #11
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QuoteOriginally posted by Raffwal Quote
LensRentals.com - "This lens is soft" and other myths

But with my K-5 I tend to get the feeling that Pentax PDAF is random at best. Sometimes spot on, sometimes nowhere even close. Perhaps it has to do with the low light color temperature like it was thought earlier, perhaps the relatively large AF area like some suspect, perhaps the position of the moon.
Turn off your SR and the randomness goes away. Try this: hold the halfshutter down until the SR hand lights up, now lift the finger off the shutter, and move the camera quickly to the left or right and you'll see the hand fade away for a full 2 sec until the hand comes back on again. If you choose the shutter speed based on SR, you'll "randomly" find soft photos when you shoot faster than your camera's SR can adjust itself for new positions. I think SR is only useful for relatively static positions, not for any quick shooting. This was extensively discussed in the later parts of Christine's thread on K5 focusing.

This isn't just a problem with Pentax's SR, there's a Nikon site where the author recommends turning off their VR system except in select situations.
02-16-2012, 01:51 PM   #12
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After reading this now I know why my Kx seems to beat my K5 on the lenses (Sigma 20mm f/1.8 and Sigma 18-50 f/2.8) I've tried on it in the same lighting conditions. It has not been as sharp and has had more noise. I can't wait to test this when I get home from work this evening.
02-16-2012, 08:41 PM   #13
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So I am not quite sure what the consensus is here. Turn the Af adjustment off and the camera focuses better? That seems odd.
02-17-2012, 03:17 AM   #14
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QuoteOriginally posted by Nick Siebers Quote
That seems odd.
Indeed.

I see three explanations:
  1. Certain firmware updates invalidate previous AF adjustment settings. Not sure how probable this scenario is, but it isn't entirely implausible.
  2. There are bugs in the AF algorithm that come into effect with certain adjustment values. Seems very unlikely.
  3. User error and/or incorrect assumptions when performing AF adjustments.
02-17-2012, 03:40 AM   #15
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QuoteOriginally posted by Class A Quote
Indeed.


I see three explanations:
  1. Certain firmware updates invalidate previous AF adjustment settings. Not sure how probable this scenario is, but it isn't entirely implausible.
  2. There are bugs in the AF algorithm that come into effect with certain adjustment values. Seems very unlikely.
  3. User error and/or incorrect assumptions when performing AF adjustments.
It could also be.... firmware updates impoved the autofoucus system !
When I downloaded to latest software there was certainly a differance.
Sat in my living room pointing my K5 at a vase of flowers I noticed as soon as I bought the camera the focussing was a bit third rate.
Before the camera would refocus there needed to be quite a bit of diferance in distance.
When I downloaded latest software I noticed that differance reduced considerably.
Now it will alter focus from the front to the back flower in the vase.
I doubt that pentax would release details of any improvements of any software for improving autofocus, since this would
be a bit like admitting there was a problem in the first place. Which of course there was lol
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