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Dot-Tune: Autofocus Fine Tuning in under 5 minutes
  
 
badlydrawnboy
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p.3 #1 · p.3 #1 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


snapsy wrote:
As for focus distance, I have preferences that have worked well for me on the lenses I use, but I don't have a grasp of all the factors involved to give general advice. For my primes I like to tune at far distances, well beyond the normal 25x to 50x focal length multipliers, and find that those tune values hold up for short distances as well. I'd suggest first trying the tune technique at any arbitrary focus distance, just to get a feel for it, and to confirm that it produces an AF tune value that yields good focus results
...Show more

Thanks Snapsy. Isn't it hard to confirm critical focus using LiveView when you're shooting from 30 feet away with a 50mm prime? That's one reason I asked; I know you mentioned earlier that you prefer to calibrate primes further away than the typical 25-50x recommendation, but I'm not sure how I could confirm accurate focus even at 10x magnification. I guess it partly depends on the size of the target. The LensAlign I normally use is pretty small.



Feb 04, 2013 at 07:34 PM
KKFung
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p.3 #2 · p.3 #2 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Many thanks Snapsy!

I tried your method for the MA on my three prime lens and the result come out is very close to what I set before which I used many real life shots to average the setting.



Feb 06, 2013 at 11:12 AM
KKFung
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p.3 #3 · p.3 #3 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Some more information share here, I also went through this process on the peripherally AF point, the different to the center point as follow:

Sigma 35/14, 2 degree

50/1.2L, 7 degree

85/1.2L, 3 degree

The coming question is what value should I set to the MA? Average the center and peripherally point or use the center point value only?



Feb 06, 2013 at 12:21 PM
snapsy
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p.3 #4 · p.3 #4 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


KKFung wrote:
Some more information share here, I also went through this process on the peripherally AF point, the different to the center point as follow:

Sigma 35/14, 2 degree

50/1.2L, 7 degree

85/1.2L, 3 degree

The coming question is what value should I set to the MA? Average the center and peripherally point or use the center point value only?


Thanks for the feedback KKFung. It's not unusual for the peripheral AF points to produce a different AF tune value than the center point, particularly for large-aperture primes. Most choose to tune for the center. Tuning for the average of the center+peripheral might produce acceptable results for both depending on what the shot-to-shot variability of your body+lens combo is; if your variability is low then you should be ok tuning to the average, otherwise you'll get a lower percentage of critically sharp photos for one or both of the AF points. I discuss variability and AF tune here.



Feb 06, 2013 at 08:20 PM
KKFung
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p.3 #5 · p.3 #5 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


snapsy wrote:
Thanks for the feedback KKFung. It's not unusual for the peripheral AF points to produce a different AF tune value than the center point, particularly for large-aperture primes. Most choose to tune for the center. Tuning for the average of the center+peripheral might produce acceptable results for both depending on what the shot-to-shot variability of your body+lens combo is; if your variability is low then you should be ok tuning to the average, otherwise you'll get a lower percentage of critically sharp photos for one or both of the AF points. I discuss variability and AF tune here.


Thanks for the comments Snapsy, I will take a chance to test these figures in actual.



Feb 07, 2013 at 03:19 AM
Todd Moon
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p.3 #6 · p.3 #6 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


This method is really nice (most of the time). Thanks for posting it! I had previously used a value of -10 for my 70-200mm f/4 IS, but this method resulted in -5 to be the best setting (at 200mm).

You don't have to check the viewfinder for the green dot if you have focus beep enabled. That's much easier than looking through the viewfinder. Just make sure you press the shutter a few times to make sure it beeps consistently.

I said "most of the time" up above because I found a situation where this technique fails. I put my 28-135mm lens on my camera and on the positive end it beeped at -7, but failed to beep at -6, so I marked down -7. Then I went to go test the far negative end and it beeped even at -20 which is the MFA limit of my 50D. (I'm not sure if other cameras go higher.) It's very unlikely that -20 is the actual limit that this lens would give me focus confirmation. It's more likely that I simply hit the limit of the MFA setting before learning the actual point where I lose focus confirmation.

To test this I set the MFA to -13 (half way between -20 and -7), turned on AF, manually focused to infinity, half pressed the shutter release, and then checked the focus in 10x Live View. It looked good. I did this about 6 more times and it would occasionally back-focus. So I did the standard "trial and error" MFA discovery technique and found that every shot looked good at -16. Even that may not be the perfect setting, but that's the first value I tried, and in my test of about 8 more focus attempts, every one looked very crisp in 10x LV.

Now, on my 70-200, the range of MFA values that gave focus confirmation was -13 to +3. That's a total range of 16. If we assume that every lens has the same width of values, then the my 28-135's range should have been -23 to -7. The middle of that being -15, which is pretty darn close to the -16 that I kept. So, for problem lenses, perhaps if you simply find one end of the range, you can just add or subtract 8 to it you have your value. However, I don't really know if that range of 16 is specific to that lens, or my camera, or not. More testing with more lenses is needed.

In conclusion, this technique is super fast and easy as long as your lens's optimal MFA value is not less than 8 away from one extreme. If it is, you have more work to do.

EDIT: The acceptable MFA range on my 50mm f/1.4 was -1 to +15. Again a range of 16. I previously had this lens set at +10, but now I set it to +7. I love how fast and easy this method is!

EDIT2: The acceptable MFA range of my 17-55mm f/2.8 at 55mm was -3 to +13. I'm definitely seeing a pattern here! At least on my 50D, the range of acceptable values is always 16 wide.

Every test was done at 50x the focal length distance from my target.



Feb 08, 2013 at 02:44 AM
badlydrawnboy
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p.3 #7 · p.3 #7 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Snapsy et al.:

I just tried this. So easy and fast!

Question: should we stop increasing or decreasing at the value where it is impossible to get focus confirmation no matter how many times you press the shutter button half-way, or just when it stops locking consistently?

For example, with my 50L it started to get inconsistent at +9, but didn't completely stop being able to focus until +12. In the negative direction, it became a little spotty at -8 and stopped completely at -10.

I guess it's kind of a moot point in this case, because if I use +12 and -10 I get a +1 AFMA value. If I use +9 and -8 I still get an AFMA of +1. But I'm curious for future reference.



Feb 08, 2013 at 09:31 PM
snapsy
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p.3 #8 · p.3 #8 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Todd Moon wrote:
This method is really nice (most of the time). Thanks for posting it! I had previously used a value of -10 for my 70-200mm f/4 IS, but this method resulted in -5 to be the best setting (at 200mm).

You don't have to check the viewfinder for the green dot if you have focus beep enabled. That's much easier than looking through the viewfinder. Just make sure you press the shutter a few times to make sure it beeps consistently.

I said "most of the time" up above because I found a situation where this technique fails. I put my 28-135mm
...Show more

Thanks for the feedback! Regarding your 28-135mm, I agree, you likely received a false confirmation @ +7. One aspect of this technique which is hard to convey in words is how you have to develop a feel for what represents a consistent and reliable confirmation vs one that is marginal. The feel for this comes after using the procedure a few times. On both Canon and Nikon bodies you have to half-press the shutter (or AF-ON) several times and sometimes hold it for up to 5 seconds to see if the confirmation waivers. Additionally, on Canon bodies I've found that if there's any delay between half-pressing and the confirmation then it's likely not a confirmed AF value, even when the delay is really small. On Nikon bodies, which have a front/back rangefinder, you get more nuanced feedback about a marginal AF value from a quick flicker of one of the rangefinder arrows. With both brands though there's definitely some finesse involved.

For cases where one end of the tune range still shows consistent confirmation even at +20 or -20, you can slightly adjust the focus of the lens to shift the range closer to the center, even if that means that adjustment puts the subject OOF. With the range centered you can then determine what the range is...then apply that range to the AF tune values you originally got with the subject in perfect focus. For example, if the range is +5 to >+20, shift the focus a bit until you get a range that fits...like to -15 to +15, which will let you determine the width of the range (30 in this case), then you can apply that range to the original +5 to >+20.

You likely can't rely on the width of the range being the same across lenses on a given body. That width is determined by several factors, including DOF and target contrast. On my D800, the Sigma 35mm f/1.4 has a range of only 2 AF tune points!, whereas my 50G f/1.4 has a range of 8 points.



Feb 08, 2013 at 10:51 PM
snapsy
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p.3 #9 · p.3 #9 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


badlydrawnboy wrote:
Snapsy et al.:

I just tried this. So easy and fast!

Question: should we stop increasing or decreasing at the value where it is impossible to get focus confirmation no matter how many times you press the shutter button half-way, or just when it stops locking consistently?

For example, with my 50L it started to get inconsistent at +9, but didn't completely stop being able to focus until +12. In the negative direction, it became a little spotty at -8 and stopped completely at -10.

I guess it's kind of a moot point in this case, because if I use +12 and
...Show more

Yep, when you get your first inconsistent confirmation you definitely want to stop searching for that given direction. And it's not even uncommon to get total non-confirmation at one tune but then only a semi non-confirmation one beyond that. That's just part of the margin and tolerance built into the phase sensing mechanism of the AF system itself.



Feb 08, 2013 at 10:58 PM
myron lee
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p.3 #10 · p.3 #10 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


skibum5 wrote:
i've gotten pretty good results simply aiming at a crack in the sidewalk (or some such) at an angle and adjusting until snaps tend to center best on the crack and it works out well, or for sports, fine tuning by aiming at some player standing around and getting the grass DOF at their feet to be placed as you want it; quick and dirty but it works well and can be quickly adjusted to exact task at hand in the field



Same here. For my 35+ focal lengths, I choose to focus adjust at my "most used" distance. For my 70-200, I shoot a bubble gum wrapper on the grass far away and adjust. my 50mm, it has to be an adjustment for close range /indoor and another adjustment for far range outdoor. I use a newspaper taped flat on the wall, then adjust for sharpness viewing 10x on the LED screen. Works the best for me.



Feb 09, 2013 at 12:18 AM
 

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Todd Moon
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p.3 #11 · p.3 #11 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


snapsy wrote:
You likely can't rely on the width of the range being the same across lenses on a given body. That width is determined by several factors, including DOF and target contrast.


Good points! It must have just been a bizarre coincidence.

Regarding your 28-135mm, I agree, you likely received a false confirmation @ +7.

I'm not sure what you mean. I never mentioned +7. The range that my 28-135 gave me focus confirmation was -20 to -7, but the -20 was an artificial limit of the MFA setting.



Feb 09, 2013 at 05:29 AM
snapsy
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p.3 #12 · p.3 #12 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Todd Moon wrote:
I'm not sure what you mean. I never mentioned +7. The range that my 28-135 gave me focus confirmation was -20 to -7, but the -20 was an artificial limit of the MFA setting.


oops, typo on my part.



Feb 09, 2013 at 06:14 AM
badlydrawnboy
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p.3 #13 · p.3 #13 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


One more question: what happens if taking half the range of the AFMA values yields a number that isn't whole? i.e. in my previous example, half-way between +9 and -8 would be +0.5. Would I just round up or down in that case and try both?


Feb 09, 2013 at 01:44 PM
Zenon Char
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p.3 #14 · p.3 #14 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


This method has gone viral on all the photo forums. Has anyone compared snapsy's method to FoCal and/or Focus Tune?


Feb 09, 2013 at 03:20 PM
badlydrawnboy
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p.3 #15 · p.3 #15 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Zenon Char wrote:
This method has gone viral on all the photo forums. Has anyone compared snapsy's method to FoCal and/or Focus Tune?


I've used all three. I'd rank them as follows:

1. Snapsy method: easiest, most accurate and fastest.
2. FocusTune: more accurate than FoCal, but more time consuming and "subjective"
3. FoCal: faster than FocusTune, but less accurate and consistent.

A lot of people love FoCal, but I've never had consistent results with it and it's come to the point where I can't trust the values it gives me.



Feb 09, 2013 at 04:33 PM
Fred Miranda
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p.3 #16 · p.3 #16 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


snapsy wrote:
A) When you get your first inconsistent confirmation you definitely want to stop searching for that given direction.
B) On Canon bodies I've found that if there's any delay between half-pressing and the confirmation then it's likely not a confirmed AF value, even when the delay is really small.


Thanks for posting this snapsy. This is a VERY important information. I started getting inconsistent results, but after applying the above, initial results in a couple lenses were dead-on.
Fred



Feb 09, 2013 at 07:34 PM
Zenon Char
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p.3 #17 · p.3 #17 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Interesting. I have FocusTune and used it a few times. I will snap some more lenses next week and see.


Feb 09, 2013 at 07:35 PM
schlotz
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p.3 #18 · p.3 #18 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


tag....


Feb 10, 2013 at 02:57 PM
Zenon Char
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p.3 #19 · p.3 #19 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


Fred Miranda wrote:
Thanks for posting this snapsy. This is a VERY important information. I started getting inconsistent results, but after applying the above, initial results in a couple lenses were dead-on.
Fred


Yes very important. Thanks for posting. I often wonder what the cut off point should be and sometimes at the outer limits, let's say +12 for example it is instant. Then at +13 it takes 4 to 5 presses. Then at +14 it takes 2 to 3 and this does change when you re- test. At one time +16 had no confirmation and the next time it hunted @ +20.

I like that - quit when it does not react instantly. So when you coming out with software?



Feb 10, 2013 at 05:57 PM
Zenon Char
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p.3 #20 · p.3 #20 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes


I guess the old keeping the target parallel to the sensor is still important. I have lens align which does a great job but may be to small to get LV focus accurate.

I may have missed this. What is everyone doing here? I just turned on my camera level and spin it 360 degrees until it was level in all directions. No guarantee my wall is level to that degree of requirement.




Feb 10, 2013 at 06:19 PM
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