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05-23-2018, 10:09 PM   #31
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QuoteOriginally posted by DimC Quote
I've got a -10 to +2 on one of my lens. I then checked with traditional method and got a -5. I went for -5 on this lens.
So, you assumed the same thing I did: that if you had more steps, the next one would be out of focus. It's too bad there isn't an empirical way to determine this, but Pentax just didn't give enough steps.

05-23-2018, 11:52 PM   #32
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QuoteOriginally posted by asharpe Quote
So, you assumed the same thing I did: that if you had more steps, the next one would be out of focus. It's too bad there isn't an empirical way to determine this, but Pentax just didn't give enough steps.
I have not tried the dot-tune method, but using the old fashioned method of a test chart at a 45 degree angle you should notice a very big difference between -10 and +10.

A few pointers:

Camera on a tripod triggered either remotely or with 2 sec timer.
Widest aperture set. (This wont affect the AF itself but will make assessing the results easier)
Natural light if at all possible (some artificial light can affect AF accuracy)
Centre point AF ONLY. The AF point must be over the black line in the centre of the chart.
Make the AF work to achieve focus by making it start each time from either closest focus distance or infinity. Putting your hand in front of the lens and pressing the shutter halfway is usually good enough to achieve this.

Assess the results of each capture by zooming the LCD display to 100% view. This will be sufficient rather than having to download your pictures to a computer, but if you do then you need to look at them full size at 100% view.

Do not rely on one attempt to assess the result. Do about 10 captures as outlined above at the default (0 adjustment setting) and then make an adjustment based on the majority. Then repeat.

Do not rely on the green hexagon.

If you still have problems then post the results of your testing on here.

ps. When you make an adjustment are you saving it as an individual lens AF adjustment or as a "global" adjustment that will apply to all lenses?
05-24-2018, 09:36 AM   #33
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QuoteOriginally posted by pschlute Quote
I have not tried the dot-tune method, but using the old fashioned method of a test chart at a 45 degree angle you should notice a very big difference between -10 and +10.
Camera on a tripod triggered either remotely or with 2 sec timer.
... (nice list of steps omitted for brevity)
QuoteOriginally posted by pschlute Quote
ps. When you make an adjustment are you saving it as an individual lens AF adjustment or as a "global" adjustment that will apply to all lenses?
Yes, all good suggestions, and all those steps are what I have done. Like I said, I'm an engineer, and a stickler for details. The adjustments were done as individual adjustments. But as a test, I also reset all settings, and then redid all the tests with both global and individual.

But I think, now that I have done DimC's test, and saw that the camera couldn't achieve focus on some negative steps of adjustment, I think I understand what is going on. In fact, there probably is indeed a difference between the adjustment steps, visually, using a angled chart. BUT. I plan to use the 55-300 mostly at 300, and at 5.8 (maximum aperture of the lens at that focal length, too much DoF at that aperture, and of course not the sharpest aperture for the lens (DxOMark tests notwithstanding)) I don't think there was enough *visible* difference between the steps (at least for me), especially since DimC's tests confirmed some degree of back focus, and showed that I didn't have enough correction steps to fully bring the acceptable focus to 50% in front, and 50% in back.

All and all, this has been an interesting exercise, and I'm going to try some other of my lenses with DimC's test, only because the other tests -- 3 different kinds of angled tests, and the Moire test -- never really gave me the feedback that I was looking for.

I am interested in anyone else who has tried to focus-adjust a DAL 55-300 at 300, however, to see if they have a different result than I. But of course, different copies of the lens are going to focus differently, because I understand that while they are all acceptably within 'spec', there is a rather wide band of acceptability.

Last edited by asharpe; 05-24-2018 at 10:27 AM.
05-24-2018, 12:13 PM   #34
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QuoteOriginally posted by asharpe Quote
But of course, different copies of the lens are going to focus differently, because I understand that while they are all acceptably within 'spec', there is a rather wide band of acceptability
That is indeed true. But also each camera may itself have a BF/FF adjustment error. It is the pairing of both lens and camera together that is the important bit. Good luck.

Also worth noting that a speck of dust on the cameras AF sensor can lead to inability to AF or erratic results. So a good puff with a rocket blower in the mirror box can be advisable too.

05-24-2018, 09:21 PM   #35
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QuoteOriginally posted by asharpe Quote
All and all, this has been an interesting exercise, and I'm going to try some other of my lenses with DimC's test, only because the other tests -- 3 different kinds of angled tests, and the Moire test -- never really gave me the feedback that I was looking for.
Ok, I have tried a few other lenses I own with DimC's method ("Dot-tune"), with these results:

LensFocal LengthApertureRange of "dot" focusFocus adj value chosen
DAL 55-3003005.8-3 to +10+4
DA 50mm501.8-2 to -10-6
DA 35mm352.4+1 to +9+5
FA100 macro1002.8-6 to +60

I was originally a little concerned with the 100 macro, it is my sharpest lens, and originally tested at +3 to -9. But I tested it again, and got -6 and +6, and I believe it. I'm a little concerned that the +10 and -10 in the ranges above aren't really the end of the ranges, but Pentax only gives that much adjustment. From a quick glance at the Pentax K1 manual, it doesn't look like that has changed for the FF body.

Last edited by asharpe; 05-24-2018 at 09:38 PM.
05-29-2018, 01:55 AM   #36
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Im glad I could help you.

My Macro lens is -3 and +3 so I've gone with no fine tuning on this one.
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