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Archive 2013 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
  
 
snapsy
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p.14 #1 · p.14 #1 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


BrianO wrote:
So you're saying that Auto Focus Micro Adjustment actually moves part of the AF array within the camera? I though it was just applying a correction to the data table for how far and in which direction to move the focusable element(s) within the lens, and thus compensate for differences between the lens-to-mirror-to-AF-Array versus the lens-to-sensor distances on different lenses and bodies.


AF tune adjusts what phase differential is evaluated as "in-focus" by the AF system. There is no mechanical adjustment to the AF points, nor any direct adjustment to the direction or magnitude of focusable element movement. Changing the evaluation of the phase differential will affect the lens/focus element indirectly as part of the multiple sensing-movement operations of an AF acquisition.



Apr 15, 2013 at 04:20 AM
robinlee
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p.14 #2 · p.14 #2 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Guys, if you have a 1.4x or 2x tc on, do you retune your AFMA?

Thanks



Apr 15, 2013 at 09:28 PM
BrianO
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p.14 #3 · p.14 #3 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


robinlee wrote:
Guys, if you have a 1.4x or 2x tc on, do you retune your AFMA?


Absolutely; the extender addes its own tolerances to the camera-lens combination, and so can affect the autofocus accuracy for the better or the worse.



Apr 15, 2013 at 09:36 PM
robinlee
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p.14 #4 · p.14 #4 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Thanks Brian I did wondered if it needs re-calibrate. I ordered a Kenko 1.4x tc hopefully it will arrive for the weekend

BrianO wrote:
Absolutely; the extender addes its own tolerances to the camera-lens combination, and so can affect the autofocus accuracy for the better or the worse.




Apr 15, 2013 at 10:07 PM
jmvdigital
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p.14 #5 · p.14 #5 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Snapsy, can you give your opinion on what's going?

I am having a really hard time getting a consistent tune value. I have tested my 24mm over twenty time now, and I'm getting tune ranges from +2.5 to +8. The average (after adding them up and dividing) is +5.26.

The tune value is consistent if I don't refocus or move the camera. I have two different sized checkerboards printed (pretty much the same as the Bob Atkins target you suggest). Up close, I use the smaller spaced pattern. I have tested at 4' - 11' feet. I am manual focusing (which could account for some of the variability, but the range still seems extreme). For example, I got +8 about four times in a row on one target, then I would adjust the distance or move to the other target, and I'd get +3, +2.5, +7, +5.

It's driving me nuts. I don't understand why one minute I'll get +2.5 and the next +8.



Apr 18, 2013 at 06:29 PM
vkumar
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p.14 #6 · p.14 #6 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


A newbie question. Does the calibration depend on the camera. If you switch camera bodies do you have to recalbrate the lens?


Apr 18, 2013 at 06:36 PM
Andrew J
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p.14 #7 · p.14 #7 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


yes


Apr 18, 2013 at 06:43 PM
BrianO
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p.14 #8 · p.14 #8 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


vkumar wrote:
A newbie question. Does the calibration depend on the camera. If you switch camera bodies do you have to recalbrate the lens?


Long answer: every manufactured item will have some "tolerance" in its measurements. So a camera's sensor-to-lens-mount distance may vary slightly from body to body within the same model, to say nothing of different models. The same goes for lenses.

So when you change a lens from one body to another, or change lenses on a given body, the precise focus distance will vary. We used to just live with such tolerances, unless a given body-lens combination's tolerances add/subtracted so much as to give unacceptable focus, in which case we'd send them in to be calibrated.

Now, with AFMA, we can do these corrections ourselves, and many of us are thus much more likely to seek a near perfection that we never would have considered before.



Apr 18, 2013 at 07:12 PM
jmvdigital
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p.14 #9 · p.14 #9 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


It seems as though the exact focus you achieve in LiveView has a much bigger impact on the tune value you end up with than I thought. Meaning that any slight change in the accuracy the CDAF or your MF image focus will change the resulting tune value quite a bit.

I tested this by slightly manually tweaking the focus in front and behind what I thought was perfect focus (+/- 0.5" @ 5 feet @ 24mm) changed the tune value 10-15 points. Perhaps this is a large part of the variability in repeatable results.

The other part being that the PDAF system seems to have quite a bit of variability depending on the target type and where exactly the horizontal/vertical lines of the target lie on the sensor itself (seeing as how the sensors don't always line up exactly with the viewfinder squares).

Anyone else confirm this?



Apr 18, 2013 at 07:52 PM
snapsy
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p.14 #10 · p.14 #10 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


jmvdigital wrote:
It seems as though the exact focus you achieve in LiveView has a much bigger impact on the tune value you end up with than I thought. Meaning that any slight change in the accuracy the CDAF or your MF image focus will change the resulting tune value quite a bit.

I tested this by slightly manually tweaking the focus in front and behind what I thought was perfect focus (+/- 0.5" @ 5 feet @ 24mm) changed the tune value 10-15 points. Perhaps this is a large part of the variability in repeatable results.

Yep and this owes principally to tuning to a 2-D target (chart) since the DOF range of what appears to be critical focus may encompass quite a few number of AF tune increments, depending on the lens and focus distance. For the best precision I suggest tuning to a 3-D target like a LensAlign, which should yield more consistent results at a given focus distance. That said, certain lenses will tune differently at different focus distances - this is a property of the body+lens combo and not specific to any tuning method.

jmvdigital wrote:
The other part being that the PDAF system seems to have quite a bit of variability depending on the target type and where exactly the horizontal/vertical lines of the target lie on the sensor itself (seeing as how the sensors don't always line up exactly with the viewfinder squares).
Anyone else confirm this?

There can definitely be some variability, so you want to use the best target possible under the best or target lighting available. This will eliminate or at least reduce the target variances from the equation.



Apr 18, 2013 at 09:54 PM
 

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jmvdigital
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p.14 #11 · p.14 #11 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


snapsy wrote:
Yep and this owes principally to tuning to a 2-D target (chart) since the DOF range of what appears to be critical focus may encompass quite a few number of AF tune increments, depending on the lens and focus distance. For the best precision I suggest tuning to a 3-D target like a LensAlign, which should yield more consistent results at a given focus distance. That said, certain lenses will tune differently at different focus distances - this is a property of the body+lens combo and not specific to any tuning.


Are you saying a 3D target would be more accurate because the shooter can visualize where the focus/DOF is and if the reference focus is as accurate as possible before tuning?

snapsy wrote:
There can definitely be some variability, so you want to use the best target possible under the best or target lighting available. This will eliminate or at least reduce the target variances from the equation.


I saw in another post you mentioned you were going to do some testing in various light levels and color temperatures to see if there were differences. Did you find anything? Or is a well lit target a well lit target regardless of daylight or halogens?



Apr 18, 2013 at 11:37 PM
sperraglia
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p.14 #12 · p.14 #12 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


I read one post that talked about lighting. I am going to try over the weekend but I live in a NYC apartment so to test my 600mm I would have to do in the hallway outside my apartment where there is overhead fluorescent lighting. Will the lighting be a problem?


Apr 19, 2013 at 12:38 AM
BrianO
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p.14 #13 · p.14 #13 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


sperraglia wrote:
I read one post that talked about lighting. I am going to try over the weekend but I live in a NYC apartment so to test my 600mm I would have to do in the hallway outside my apartment where there is overhead fluorescent lighting. Will the lighting be a problem?


Is there a high-contrast object visible out a window that's about 50 (25X) to 100 (50X) feet away? If so, you could use bright daylight.



Apr 19, 2013 at 02:28 AM
sperraglia
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p.14 #14 · p.14 #14 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


BrianO wrote:
Is there a high-contrast object visible out a window that's about 50 (25X) to 100 (50X) feet away? If so, you could use bright daylight.


I could use a building across the way I guess, there is water tower that has a wave like painting on it, the only thing is it is at a slight angle. Worth a try, of course taking pictures out my window with a large telephoto might get me in trouble, I can hear it now "sorry officer I was just testing my lens". The hallway might be a less interesting option.



Apr 19, 2013 at 03:16 AM
gschlact
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p.14 #15 · p.14 #15 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


tlbradford wrote:
I read Wilba's article and his links to Doug Kerr's article and that answered most of my questions from number two. So the simplified version of #2 is this. How can you use this method to Microadjust Manual Focus only lenses? You have also stated that you can establish critical focus using manual focus for step 2. I don't understand how that is possible if we are fine tuning the camera bodies auto focus confirmation.

You do it the same way, use live view manual focus instead of the Contrast detect AF to achieve critical focus. Then proceed to walk through you MFA values to determine your range.

However, read my posts from page 12 and 13 regarding an enhanced method for offsetting g your determined value specific for manual focus lenses with the AF Confirm Chip. IF YOU DON'T HAVE AF CONFIRM CHIP none of this applies at all since MFA is only determine via the Confirming of AF.

I hope this helps.

Guy



Apr 19, 2013 at 03:38 AM
snapsy
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p.14 #16 · p.14 #16 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


jmvdigital wrote:
Are you saying a 3D target would be more accurate because the shooter can visualize where the focus/DOF is and if the reference focus is as accurate as possible before tuning?

Using a 3D target lets you tune to a precise point in the DOF range. Even if CDAF in LV were perfect it would still drop you at the 70/30 DOF balance or whatever the balance is for that lens and focusing distance, and some people would prefer to tune to 50/50.

jmvdigital wrote:
I saw in another post you mentioned you were going to do some testing in various light levels and color temperatures to see if there were differences. Did you find anything? Or is a well lit target a well lit target regardless of daylight or halogens?


I did a little testing using the ML DotTune (faster to run) and saw differences but I didn't spend much time looking into it.



Apr 19, 2013 at 05:54 AM
Lars Johnsson
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p.14 #17 · p.14 #17 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


gschlact wrote:
You do it the same way, use live view manual focus instead of the Contrast detect AF to achieve critical focus. Then proceed to walk through you MFA values to determine your range.

However, read my posts from page 12 and 13 regarding an enhanced method for offsetting g your determined value specific for manual focus lenses with the AF Confirm Chip. IF YOU DON'T HAVE AF CONFIRM CHIP none of this applies at all since MFA is only determine via the Confirming of AF.

I hope this helps.

Guy


I have not been reading the thread so I don't know what you have been writing before.
I use a lot of MF lenses on my Canon bodies. The main advantage of doing MF is that you can focus on any part or subjects in the Viewfinder. Especially when using different focus screens that you can change in your camera. That's great for composition . If you must confirm it with the center AF point, then all those advantages will go away. And it would probably be better to use Live View instead the normal MF



Apr 19, 2013 at 06:25 AM
jmvdigital
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p.14 #18 · p.14 #18 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


snapsy wrote:
Using a 3D target lets you tune to a precise point in the DOF range. Even if CDAF in LV were perfect it would still drop you at the 70/30 DOF balance or whatever the balance is for that lens and focusing distance, and some people would prefer to tune to 50/50.

I did a little testing using the ML DotTune (faster to run) and saw differences but I didn't spend much time looking into it.


Alright, here is a good riddle and cautionary note for anyone working on tuning their lenses. I have tested all manner of print targets, lighting, and various setups from indoors to outdoors. The photos below are from a simple test I did using my laptop screen as the target. Both are targets I made up in Illustrator really fast, and both, in theory, should work equally as well on dual-cross center point AF sensor in the 5D3.

The problem is that these two targets consistently test at very different tune values (i.e., the AF system reacts very differently in reading them). In the top image (with the cross-hatch grid lines), the calculated tune value works out to be around a -2. In the bottom image (with the checker board), the calculated tune value work out to be around a +8.

I shot manually focused images of both targets (focus is correct in viewing the RAW files) as a control. Then I used the PDAF system to give me focus confirmation while I focused the lens from both sides of center (one shot focusing from near->far, one shot focusing from far->near). Both gave consistent results of the near focus confirmation being slight in front of the target, and the far focus confirmation being slightly behind the target... with the mid-point between the two being perfect focus.

I don't really know what's going on here, or if my camera is "unique," but it seems as though depending on your target choice, how big you print it, and how far away you are... you could get wildly different results. Which could dovetail into the realworld if the AF system does indeed have some sort of front/back bias depending on your subject.

Anyone care to explain?






24mm @ 5': Target 1 (Tests at a -2 tune value)







24mm @ 5': Target 2 (Tests at a +8 tune value)




Apr 19, 2013 at 04:29 PM
Wahoowa
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p.14 #19 · p.14 #19 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


jmvdigital wrote:
Anyone care to explain?


I have yet had any explanation for it, but I would like to suggest you to do one more experiment. Print out both targets and try them. I might have an explanation afterward. Cheers.



Apr 19, 2013 at 04:44 PM
jmvdigital
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p.14 #20 · p.14 #20 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


A little bit more testing using a sheet with half white, half black with a solid. With the vertical line, the tune value is +7. With a horizontal line, the tune value is a -1.5.

What gives? Obviously, the AF sensor is reacting differently to horizontal and vertical information. My question is, is this normal? Anyone else with a 5D3 experiencing this? My camera is new... wondering if I should exchange it.

EDIT: The focus difference appears to be the largest with my 24mm TS-E. With the 14L, 35L and 100L, the difference is about 2-3 points instead of 5-6.











Edited on Apr 19, 2013 at 05:24 PM · View previous versions



Apr 19, 2013 at 04:45 PM
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