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06-25-2020, 02:07 PM   #16
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QuoteOriginally posted by Wheatfield Quote
Heck, if you really want to, you can take a picture of a newspaper taped to a wall ............
Oooh, that's a good idea. I have been looking for calibration charts but, say, a photography mag with images would work fine. When I first asked this question I wondered if it was a daft one but it has been really informative.

06-25-2020, 02:42 PM - 1 Like   #17
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QuoteOriginally posted by Cerebum Quote
Oooh, that's a good idea. I have been looking for calibration charts but, say, a photography mag with images would work fine. When I first asked this question I wondered if it was a daft one but it has been really informative.
It's the best method I've found. Find a flat object, and focus on it. I've tried the yardstick method, I downloaded the Nikon D70 focus test chart (it seems to be no more) and tried it. Yvon Bourque, our late and dear friend, invented one of his own which I tried, but I've always gone back to the basic brick wall style of test. What I found with the rulers and charts was that the set up was very fiddly, and the results were not reliable because the AF sensor didn't necessarily lock onto the exact same location of the chart each time, rendering the exercise a total waste of time and effort.
By setting up a flat object to focus on and getting the sensor parallel to it , there is zero possibility of the sensor locking onto something at a different distance and ruining the test.
It doesn't matter what you use, but do take the time to make sure the focal plane (sensor) is close to parallel to it. I like a newspaper because it is fine print, but any printed page would do.
What makes it easier to align the set up is a rectangular target, as if there is no geometric distortion of it in the viewfinder, you know you have an accurate set up.
As was mentioned, the approach has to be rigorous. It's not piano building, but the more accuracy you bring to the process the better your final result will be, meaning sharper images and taking full advantage of the not insignificant investment you have made in your camera gear.
06-25-2020, 03:02 PM - 2 Likes   #18
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QuoteOriginally posted by Wheatfield Quote
It does require some discipline, but there are so many ways to do it,
Once I realized my K1 was backfocussing on average requiring +7 to correct, my favourite trick with a new lens is to focus on a wine bottle label. It needs to be one with a long name !
06-25-2020, 03:27 PM - 2 Likes   #19
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QuoteOriginally posted by pschlute Quote
Once I realized my K1 was backfocussing on average requiring +7 to correct, my favourite trick with a new lens is to focus on a wine bottle label. It needs to be one with a long name !
Motto: Cabernet Sauvignon, tastes awful, and it works.

06-26-2020, 01:03 AM   #20
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QuoteOriginally posted by Wheatfield Quote
It's the best method I've found. Find a flat object, and focus on it. I've tried the yardstick method, I downloaded the Nikon D70 focus test chart (it seems to be no more) and tried it. Yvon Bourque, our late and dear friend, invented one of his own which I tried, but I've always gone back to the basic brick wall style of test. What I found with the rulers and charts was that the set up was very fiddly, and the results were not reliable because the AF sensor didn't necessarily lock onto the exact same location of the chart each time, rendering the exercise a total waste of time and effort.
By setting up a flat object to focus on and getting the sensor parallel to it , there is zero possibility of the sensor locking onto something at a different distance and ruining the test.
It doesn't matter what you use, but do take the time to make sure the focal plane (sensor) is close to parallel to it. I like a newspaper because it is fine print, but any printed page would do.
What makes it easier to align the set up is a rectangular target, as if there is no geometric distortion of it in the viewfinder, you know you have an accurate set up.
As was mentioned, the approach has to be rigorous. It's not piano building, but the more accuracy you bring to the process the better your final result will be, meaning sharper images and taking full advantage of the not insignificant investment you have made in your camera gear.
Thanks for the detailed info what distance do you use? Or do you just set up so you can get one page in frame?
06-26-2020, 03:03 AM   #21
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How's this for a calibrator. There is a ridge with a flat face to the left of this weathered post. I used that to calibrate. The lovely thing is you can see your dof and where its centred

06-26-2020, 03:36 AM - 1 Like   #22
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QuoteOriginally posted by Cerebum Quote
How's this for a calibrator
The important thing is that you use only centre point AF , and that where it is pointing is unequivocal and of sufficient contrast. Can you be sure which of those ridges is getting focus lock ? They are probably close enough together not to make much difference. Also, do not rely on 1 go at AF. Do about 10, making the camera work each time from both minimum focus distance and infinity.If you get around 8/10 that are spot on accurate then that is the setting to go with.
06-26-2020, 07:49 AM   #23
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QuoteOriginally posted by Cerebum Quote
How's this for a calibrator. There is a ridge with a flat face to the left of this weathered post. I used that to calibrate. The lovely thing is you can see your dof and where its centred

Ummm, not so much. To me there is too much depth in the object to know precisely where the focus point is going to rest from shot to shot. The AF sensor is surprisingly large, much larger than the little red spot in the viewfinder would have you believe. However, if it worked for you, that's excellent.
Depth of field shouldn't really be a factor in AF adjustment as it should be done wide open to limit it as much as possible anyway.
OTOH, it is certainly a subject worthy of some photographic attention.

---------- Post added Jun 26th, 2020 at 08:50 AM ----------

QuoteOriginally posted by pschlute Quote
The important thing is that you use only centre point AF , and that where it is pointing is unequivocal and of sufficient contrast. Can you be sure which of those ridges is getting focus lock ? They are probably close enough together not to make much difference. Also, do not rely on 1 go at AF. Do about 10, making the camera work each time from both minimum focus distance and infinity.If you get around 8/10 that are spot on accurate then that is the setting to go with.
^^^^^^^^^^^^^^^^^^^^^this^^^^^^^^^^^^^^^^^^^^^^^

06-26-2020, 08:03 AM   #24
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Use the chart at the end of this article. Print it and secure it to something solid. Capture it at a 45 degree angle


http://www.kscameraclub.org/docs/pdfs/focus_test_chart_edited.pdf
06-26-2020, 08:17 AM   #25
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QuoteOriginally posted by pschlute Quote
Use the chart at the end of this article. Print it and secure it to something solid. Capture it at a 45 degree angle


http://www.kscameraclub.org/docs/pdfs/focus_test_chart_edited.pdf
That's the D70 chart I was alluding to. It works well.
I saw that page, I guess I didn't scroll down far enough.
06-26-2020, 10:27 AM   #26
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QuoteOriginally posted by pschlute Quote
The important thing is that you use only centre point AF , and that where it is pointing is unequivocal and of sufficient contrast. Can you be sure which of those ridges is getting focus lock ? They are probably close enough together not to make much difference. Also, do not rely on 1 go at AF. Do about 10, making the camera work each time from both minimum focus distance and infinity.If you get around 8/10 that are spot on accurate then that is the setting to go with.
What I actually did was fasten a magazine on the back of a chair in the conservatory (the brightest room) I set the kp to iso 100, wide open, ibis off (on a tripod) and made the lens work by focusing on my hand in between calibration shots, I then went to the extremes and worked my way in to the sharpest zone. When I was doing zooms I went for mid range, 125mm on the 50-200 etc, is that the best way of doing a zoom? Also, how critical would you say distance is? I was from 1-3 meters, depending on focal length.

---------- Post added 06-26-20 at 10:29 AM ----------

QuoteOriginally posted by pschlute Quote
Use the chart at the end of this article. Print it and secure it to something solid. Capture it at a 45 degree angle


http://www.kscameraclub.org/docs/pdfs/focus_test_chart_edited.pdf
I will print this off, thank you

---------- Post added 06-26-20 at 10:30 AM ----------

QuoteOriginally posted by Wheatfield Quote
.
OTOH, it is certainly a subject worthy of some photographic attention.
Cool isn't it
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