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Old Apr 4, 2009, 11:22 AM   #1
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Has anyone done the AF test on their lenses yet and adjusted in the K20?

Before I do anything here to adjust, I'd like to confer with someone on this. I set up on my leveled tripod, SR off, each lens to largest aperture at the length tested, using remote control. First I had printed out the test sheet that Yvon Bourque presents. Then, I printed out Tim Jackson's and rather than laying flat and getting my tripod to 45ยบ, I paperclipped to Yvon's chart. But, either test I use yields front focusing issues.

I have the following lenses:

Pentax 18-55mm at 4.5, 50mm at 1.4, 50-200mm at 4.0

Tamron 70-300mm at 4.0

Sigma 28-80mm at 3.5

Everyone except the Tamron isdefinitely front focusing. Unless I did the test wrong. The Sigma is focusing all the way at the front focusing 80mm mark.

Any advice welcome.

Patty
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Old Apr 4, 2009, 11:36 AM   #2
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Every lens I have required some adjustment for best results. The only lens of mine that back focused was my DA 35mm Macro. The rest front focused requiring adjustment from -2 to -10. The -10 was my newest Sigma 150- 500mm wich may have benefited in -11 to -12 (not availabe) but is working well at -10. Just set up carefully and keep testing different adjustments until you go past optimum.

Ed

Photo from Sigma 150 500mm adjusted to -10
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Old Apr 4, 2009, 12:20 PM   #3
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Patty,

Thanks for taking the lead on this. I have just been shooting away, trying out other things and letting this go. I have not really noticed anything yet, but I have not really looked that closely either, nor have I tried out all of my lenses. The ones I am really interested in are...
Pentax 10-17
Pentax 12-24
Pentax 16-45
Pentax 55-300
Pentax 50 1.7 M
I am also wondering if using the remote control software would make the process go a bit faster? Just thinking out loud.
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Old Apr 4, 2009, 2:25 PM   #4
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interested_observer wrote:
Quote:
Patty,

Thanks for taking the lead on this. I have just been shooting away, trying out other things and letting this go. I have not really noticed anything yet, but I have not really looked that closely either, nor have I tried out all of my lenses. The ones I am really interested in are...
Pentax 10-17
Pentax 12-24
Pentax 16-45
Pentax 55-300
Pentax 50 1.7 M
I am also wondering if using the remote control software would make the process go a bit faster? Just thinking out loud.
I am not sure about quickest way, but the time is well spent. Ijust looked at my past adjustments and my DA 16 - 45mm f4 required a +8 adjustment.

Ed

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Old Apr 4, 2009, 2:40 PM   #5
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Thanks, Ed.

Okay, so it's not unusual that all my lenses could use adjusting then. I thought maybe I was doing it wrong.

Does it make a difference where in the focal length you test? I had been trying to be at the widest length on my zoom lenses. But, am realizing when I retested I forgot to set them that way.

The Sigma 28-80 that was the worst needed more than -10. But, it's pretty good there. Actually, I'm assuming I keep adjusting until I get equal levels of focus on either side of the center. Right?

Now that I'm looking at them on the computer, I'm going back for a second try. So far I've adjusted the 18-55 to -8 and think maybe -9 would be just a smidge better. My 50-200 is set to -10 and is still not in even focus. The 70-300 that I thought was pretty good I set to -8 and it's looking now like -10 would actually be perfect. And, the only one that didn't require a ton of changes is my 50mm. I set it to -3, but might up to -4.

Yes, IO, doing the remote control software would definitely make this go quicker. I may get my laptop out and try it. I've been going back and forth between the computer and the camera with my card. :idea: I hadn't thought of using the software.

Anyway, my findings so far. I guess the real test will be when I take some actual photos. I know I've always been disappointed with how clear some of my images were at times. Maybe I should have done this a long time ago. (Well, only Christmas.)

Patty

p.s. I know I can't adjust on the K100, but now I'm curious how much they'd be off if I put them on it.
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Old Apr 4, 2009, 3:06 PM   #6
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Quote:
p.s. I know I can't adjust on the K100, but now I'm curious how much they'd be off if I put them on it.
I do not know for sure, but I believe the adjustment is to the position that the camera places on the sensor and has nothing to do with any adjustment the actual lens. I am also thinking that since the camera knows what lens is mounted, keeps a table of lens adjustments and applies them as the lenses are mounted.

I have to go and get some bales of Timothy/Orchard grass for my wife's critters. #2 son has to unload them (before going off to work), since the doctor told me no lifting until my surgery.... getting old is the pits.
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Old Apr 4, 2009, 3:34 PM   #7
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True, IO, on the K100. Guess I was looking at the trees and didn't see the forest.

Okay. Now I just went back and readjusted the 18-55 back to -8 as -9 was just too much. But, then I needed to adjust back to -7 when retested and seems it could go back to -6. Also, noticed I was at 18mm and earlier I had been at 43mm.

I've got scribbles all over of the different images and what the setting was on the camera. I wish the image would record what +/- setting it was taken at. I'm getting them all mixed up now.

Time to take a break from this for a little while.

Patty
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Old Apr 4, 2009, 4:12 PM   #8
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I usually test at the longest focal length, widest aperture, closest focus distance the lens will allow. This gives you the smallest depth of field and is easier to tell the differen.

Yes, you want equal distance in focus on either side if you are using a chart that graduates the distace to allow for perspective. If you are using a ruler you would expect more in focus behind the focus point.

The adjustment is in the camera, you can not adjust two of the same model lens if they require different adjustment level.

Make sure the angle is as close to 45 deg. as possible. This makes a difference.

Ed

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Old Apr 5, 2009, 9:29 AM   #9
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Are you using single spot focus or multi spot focus? Reason I ask, I found my Sigma 24-135mm lens to yield backfocus when I was using the multispot focus which I could correct with an adjustment of -6, but if I set it to single spot focus it has been spot on with it set to 0. Just an observation.
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Old Apr 5, 2009, 11:15 AM   #10
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Quote:
Are you using single spot focus or multi spot focus?
MadMike's question brings up an interesting point. Maybe it is "intuitively obvious to the casual observer", but functions like the front/back-focus calibration & adjustment, that the K20, has begs for some instructions from the manufacturer. It certainly appears to me that the engineers had a specific procedure in mind with this option. It would be good if in the manual they would have spelled it out, rather than letting us guess their intent.

These systems, and they are systems - make no mistake about it, offer so many adjustments and controls, that when used in various combinations provide for an endless array of results - intended or unintended.

.... but I digress, back to MadMike's question or observation. I have not started down this path - yet. However, to my mind, single spot focusing, would be (now after the question) the obvious way to go. Before MadMike's observation, I would have probably not even thought of it, until I had "tuned" all the lenses up and started wondering why all of them were off by %$#@.

Now that a couple of these questions have come up like:
  • On a zoom lens, what focal length - near or far, or somewhere in the middle?[/*]
  • What f stop would be best given the dof issue - the lowest f value?[/*]
  • Single spot focus or multiple spot focus?[/*]
  • etc....
    [/*]
So I went looking and found a few sites that seemed to address the issue - I have not read them all, but did a quick scan through them and these seemed to apply (in no particular order, than how I came across them)...I also came across this, that I thought was interesting. It explains the problem, however with the K20's adjustment, we do not have to make any mechanical adjustments. Also, their setup seems to be very old, given Yvon Bourque target, which when compared to others that I have seen, is a real elegant fit of genius. Overall, I have suffered with death by a thousand cuts on a number of issues over the years at work. So, I'll continue to read here to see how all of this turns out and what everyone decides on and comes up with....




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