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03-06-2014, 05:59 AM   #1
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Adjusting the fine focus on K-x...

A couple of days ago I shot some test shots wide open with a Pentax M 1.4/50 and noticed a slight focus error. I went into the debug menu & the AF Test adjust value was 0. I checked my other K-x & yep... also zero. I know I set these up quite some time ago, but they have been sitting for about a month with no batteries, so apparently they lose the setting data if they lose power for a long time.

Anyway, I spent hours with several lenses 'til I was googly-eyed last night, setting up the AF detect point. Most of my lenses (and all of my fast ones) are manual focus, so I used the 1.4/50 wide open to set up the AF detect point with catch in focus. I had a static target about 4 feet away of newsprint taped to a wall, and using catch in focus, turned the focus ring slowly until it fired, then turned the focus ring to the other side of the focus point and repeated the procedure, turning the ring in the opposite direction until it fired. Focus accuracy was confirmed via the camera LCD, zoomed in to the center focus point. I did this a few times until the bulk of the shots were in focus, then I confirmed focus accuracy with other fast MF lenses and my 3 slower AF lenses wide open at targets of different distances. I also verified using a ruler placed at a 45 degree angle, comparing the out of focus zones to the front and rear of the center focus point.

The lenses I used to verify the adjustment were:

MF lenses:

Pentax M 1.4/50mm
Pentax A 1.7/50mm
Ricoh Rikenon XR 2.8/28mm

AF lenses: (The only AF lenses I have)

Tamron XR Di 18-200
Pentax DA 55-300
Pentax DA 10-17 fisheye zoom

I have several other MF lenses I didn't use, because they have a maximum aperture of 3.5 or smaller.

Here's my dilemma:

1) Most shots with all lenses are in focus when you zoom up super-super close, but a few aren't quite in focus. It's random.

2) Most lenses aren't razor sharp wide open. My Pentax 1.4/50 and Pentax 1.7/50 are probably the sharpest wide open lenses I have, but still they aren't as sharp as when stopped down a notch. All of my AF lenses are zooms. (Tamron XR 18-200, Pentax DA 55-300, and Pentax DA 10-17) and none of these are super sharp wide open.

3) When testing the zooms, the focus accuracy wide open varies depending the focal length selected. The Tamron 18-200 wide open is soft below about 35mm, the Pentax DA 55-300 is soft wide open under about 100mm, but the DA 10-17 is pretty consistent through the range.

Since I can't get it to the point where every single shot from every lens is sharp, and my zooms are a bit soft wide open, how do I know when I really, truly have it nailed? Or am I just driving myself nuts with this?


Last edited by GibbyTheMole; 03-06-2014 at 06:04 AM.
03-06-2014, 08:34 AM   #2
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You are driving yourself nuts.
Getting the adjustment right for one lens means you might be off on another. That`s why k-7, k-5, k-3 allow individual lens settings. All you can do on k-x is best average.

On zooms you need to select the focal length you use most or again, find the best average.

The accuracy of testing is also a problem, sometimes the margin of error exceeds the original error, so you are just guessing randomly.

Unless you want to write down individual settings for each lens and change them when you change lenses a good average is the best you can get.
03-06-2014, 08:40 AM   #3
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Heh, my k-x itself is about -80 micrometers adjustment required before any lenses is put on it. I blame my friend, he dropped the camera a while ago.

I've found that it's better to find a compromise. I set my AF settings to meet my fastest lens - DA*55 F1.4. Then from there, my Tamron 70-200 is mostly accurate up till 150mm, where it then has quite a bit of front focus. I basically work-around that by aiming a little further than my target.

I can't wait until I get a k-3 with individual adjustments.
03-06-2014, 08:51 AM   #4
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QuoteOriginally posted by GibbyTheMole Quote
My Pentax 1.4/50 and Pentax 1.7/50 are probably the sharpest wide open lenses I have, but still they aren't as sharp as when stopped down a notch.
That is true of every variable aperture lens ever manufactured.
QuoteOriginally posted by GibbyTheMole Quote
3) When testing the zooms, the focus accuracy wide open varies depending the focal length selected
Quite common
QuoteOriginally posted by GibbyTheMole Quote
I had a static target about 4 feet away of newsprint taped to a wall, and using catch in focus, turned the focus ring slowly until it fired,
Not the best method. When you use auto focus the camera stops the focusing procedure before firing the shutter. When you use catch-in-focus you are still turning the focus ring at the time the picture is taken. Granted, the amount may be small, but when testing or adjusting something it's best to eliminate as many variables as possible.

03-06-2014, 08:56 AM   #5
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One method that I liked using was the averaging method -

1) Take lens, put on tripod with camera. Manually focus on high contrast subject in liveview.
2) Turn off liveview so you are using phase detect. Set microadjust to some arbritrary but definitely OOF value (+100 micrometers, for example).
3) Press shutter button halfway to see if hexagon lights up in the viewfinder.
4) Change your microadjust value by -10, and repeat shutter press.
5) Do this until you see the green hexagon appear - record the value. Must be a solid clear green hexagon, not blinking.
6) Continue subtracting 10 micrometers until the green hexagon starts being intermittent. Record this value.
7) Average the two values and you will get the "middle-ish" adjustment value that puts your focus within it's sweet zone.

It's critical to make sure the camera and tripod are rock steady so when you press the shutter halfway, it doesn't move the setup.
I used this to great effect on my lenses.
03-06-2014, 10:22 AM   #6
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QuoteOriginally posted by JinDesu Quote
One method that I liked using was the averaging method -
Great idea! I will probably give that a shot.

---------- Post added 03-06-2014 at 11:26 AM ----------

QuoteOriginally posted by Parallax Quote
I had a static target about 4 feet away of newsprint taped to a wall, and using catch in focus, turned the focus ring slowly until it fired,
Not the best method. When you use auto focus the camera stops the focusing procedure before firing the shutter. When you use catch-in-focus you are still turning the focus ring at the time the picture is taken. Granted, the amount may be small, but when testing or adjusting something it's best to eliminate as many variables as possible.
The reason I did it that way is because the only fast lenses I have with a very narrow DOF are manual focus. I turned the ring extremely slowly, though.
03-06-2014, 10:28 AM   #7
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I remember those days when I thought everything should work perfectly under any conditions. Lenses are just tools, not miracle workers. For example fast lenses are not built to shine wide open on a distant subject. I see people shooting landscape with a 50mm f1.7 wide open on a sunny day and get disappointed with the result, and then try to micro-adjust everything....
03-06-2014, 10:32 AM   #8
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QuoteOriginally posted by nicoprod Quote
I remember those days when I thought everything should work perfectly under any conditions. Lenses are just tools, not miracle workers. For example fast lenses are not built to shine wide open on a distant subject. I see people shooting landscape with a 50mm f1.7 wide open on a sunny day and get disappointed with the result, and then try to micro-adjust everything.
Very true... I just want to get it to the point that when I do low light work with a fast lens, it's in focus as closely as possible.

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