DotTune MFA question...

[ErikH]

Hi - I just MFA my 70D using the "DotTune" method outside on a bright day with 2 of my lenses. Here are my results and my questions below:

55-250 STM

(W)ide -8 +5 = -1 (or -2)

(T)ele -5 +3 = -1

18-135 STM

W -6 +5 = 0

T -7 + 5 = -1

1) Because my adjustments are so minimal, is it even worth making the change? The reason I'm asking, is (if I'm understanding correctly) this method balances the focal plane evenly whereas typically the focal plane is thought to be 1/3 in front & 2/3 behind (speaking generally).

Since my camera has a (slight) tendency toward the minus side, could that be part of the correction DotTune is trying to make to even "things" out? (hopefully that makes sense).

Any comments appreciated!

 

[Zeee]

and keeping the most relevant ones. This appears this was released before the manufacturers added MFA at both ends. I'm not posting this to say not to MFA. Do whatever you want.

 

[WilbaW]

Let's not forget, the inch of total DOF is not "in focus". It is, in theory, not noticeably out of focus to someone with ordinary eyesight viewing an image under the conditions assumed in the calculation. Those assumptions don't apply for instance if you're peering at the image at 100% on a nice big monitor.

I did say there is a little room for error for that.

I was referring to you have a total DOF but all the 8 increments may not be in perfect focus. For example 1 and 9 might start blurring.

Okay, well there are a few things we can say about that. It's easier if we think about 0 at the plane of focus, and minus and plus from there. It's important to understand that any position away from the POF is actually out of focus, IOW, - 1, +2, - 3... are all OOF, but - 5 and +5 should be on the edge of where people with ordinary visual acuity might start to notice it, if they are looking at an image for which the COC was chosen. If they are looking at an image under different conditions, e.g. from closer than the image diagonal or with better than average visual acuity, - 3 to +3 might be perceived as OOF. Or if they are looking at an image from many times the image diagonal, - 12 to +12 for instance might appear to be in focus.

The crucial thing to understand is that DOF is entirely about viewer perception. It has no meaning other than that.

It was late and I meant 1 and "8" (not 9) might start blurring but that was just an example.

I know.

It could starting much sooner.

Sure, but I'm not certain you have your head around why and how, and I worry that's getting in the way.

It will vary depending on the f stop.

Do you mean when comparing lenses with different max. apertures, or with the same lens? If you're thinking of the same lens, then no, AF is with the aperture wide open and everything we're talking about relates to that, so no dependence on aperture for the DOF referred to in AF MA discussions.

Of course DOF will vary with aperture for exposures, but in that case 1/8 of that DOF is irrelevant - you just want the plane of focus on the subject, and you can adjust its position by + or - 1 or more increments. That's all there is to it.

The beginning of that paragraph in the link is interesting as well. The adjustments are no based on depth of field, not focal length which again confirms what we have concluded.

Please state exactly what we have concluded ('cos I have no idea what that is).

 

[WilbaW]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

 

[Mr Ed M]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

Where did you come up with that?

Yes focus is done by a different sensor, but, the DOFs, focus or field, are impacted by the same physical rules and properties. The size of both DOFs will vary with subject distance.

 

[Zeee]

Let's not forget, the inch of total DOF is not "in focus". It is, in theory, not noticeably out of focus to someone with ordinary eyesight viewing an image under the conditions assumed in the calculation. Those assumptions don't apply for instance if you're peering at the image at 100% on a nice big monitor.

I did say there is a little room for error for that.

I was referring to you have a total DOF but all the 8 increments may not be in perfect focus. For example 1 and 9 might start blurring.

Okay, well there are a few things we can say about that. It's easier if we think about 0 at the plane of focus, and minus and plus from there. It's important to understand that any position away from the POF is actually out of focus, IOW, - 1, +2, - 3... are all OOF, but - 5 and +5 should be on the edge of where people with ordinary visual acuity might start to notice it, if they are looking at an image for which the COC was chosen. If they are looking at an image under different conditions, e.g. from closer than the image diagonal or with better than average visual acuity, - 3 to +3 might be perceived as OOF. Or if they are looking at an image from many times the image diagonal, - 12 to +12 for instance might appear to be in focus.

The crucial thing to understand is that DOF is entirely about viewer perception. It has no meaning other than that.

It was late and I meant 1 and "8" (not 9) might start blurring but that was just an example.

I know.

It could starting much sooner.

Sure, but I'm not certain you have your head around why and how, and I worry that's getting in the way.

See my explanation in your next post.

It will vary depending on the f stop.

Do you mean when comparing lenses with different max. apertures, or with the same lens? If you're thinking of the same lens, then no, AF is with the aperture wide open and everything we're talking about relates to that, so no dependence on aperture for the DOF referred to in AF MA discussions.

Of course DOF will vary with aperture for exposures, but in that case 1/8 of that DOF is irrelevant - you just want the plane of focus on the subject, and you can adjust its position by + or - 1 or more increments. That's all there is to it.

If you look at the edges of the total DOF that is in focus based on the online DOF chart there will be a wider blur area at f1.2 than there will be at f11.

The beginning of that paragraph in the link is interesting as well. The adjustments are no based on depth of field, not focal length which again confirms what we have concluded.

Please state exactly what we have concluded ('cos I have no idea what that is).

Let's see. There is a mathematical value to DOF as explained by Canon which no one had an answer to when this started. That DOF value varies depending on input. There was never a solid explanation to why there were different suggested distances to targets and how final results could have been affected by that. That was all over the board as far as I was concerned and no one never ever had a real answer to that and I did ask for 5 years. Canon stated that you may not see major shifts of up to +-5 and I was much more forgiving on that one. Those are a few to start.

I'm just trying to get some answers to this. I'm trying to understand what you are looking for? Are you saying this is all fiction and there has been nothing new has been brought to the table?

 

[Zeee]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

Then why is Canon saying ⅛ for depth of field if it is irrelevant? There is no "depth of focus" in that document. I'm saying that it does not exist. Why did Canon even provide that information?

@ 5 ft to target we get eight 0.015 increments. At 50 ft to target we get eight 1.89 increments. I'm not a technician but it seems logical 1.89 would be more forgiving to work than 0.015.

I get that if you move MFA +-1 the focus point shifts but it still can be within an area that was previously in focus. The DOF follows. Eventually as you keep increasing the MFA value the focus point will go into an area that was out of focus from the first reading. How else do you explain where Rudy says you may not see a change if up to 5 MFA moves?

If this is not correct please explain what Canon means by ⅛ of depth of focus and why are there so many different instructions of distance to target and why even Canon contradicts itself? There has to be a value because everything is math.

 

[Zeee]

This is how I see it based on doing this with rulers at one time. It is difficult to show this on a flat plane so this is a ruler on an angle.

The red lines represent the area that is was in focus originally at 0 MFA. The yellow areas are out of focus. Green is the focus point.

Column A is 0 MFA. B = 1 MFA shift. C= 2 MFA shifts. D = 3 MFA shifts.

The AF point in column D is still within the area that was in focus in column A - between the red lines.





According to Canon and the DOF chart the distance within the bracket that is in focus changes if you alter the distance to your target thus so do size of the increments.

I'm only basing this in what I think Canon is trying to tell me.

 

[Zeee]

of MFA I always assumed a + or - move was a single fixed value if you did it at 2 ft or 1000 ft. Be it .0625, .125 or whatever number Canon used. That to me would be irrelevant. It seemed logical.

But now this ⅛ of the Depth of Field comes out. Well Canon provided a value of ⅛ of something so that "something" must have a value as well.

Even if each MFA value is fixed it will make a huge difference with distance. With my example the total DOF of 1.89 at 50 feet or 0.015 at 5 feet there is no way to divided that by 8 with a fixed value move.

I know that if I take a landscape shot there is infinity. There is a rock 30 feet from me and a tree 10 feet behind that. I can focus on the tree or the rock and everything will be sharp. So there is a zone that will keep images sharp and it gets tighter as the focal length gets longer.

Also about the blur zone. Easier to describe with a diagram. The white are represents what is in focus, the grey is the blur zone and yellow is OOF. I believe the blur zone is shorter at f11 as opposed to F1.2 but I could be wrong. That was what I was trying to explain.



I thought I was getting somewhere. If I'm wrong I'm wrong. I have no issues with that. Perhaps moving one MFA point within an area that is in focus within the DOF area makes a huge difference based on this discussion. If someone explains this to me think of it as this is my first day using an external flash and I have no idea what happens when my camera is set to manual.

I'd still like to know what Rudy means by saying ⅛ of the Depth Of Field and how this effects MFA.

 

[HighSierra]

Isn't the whole point of MFA to fix a situation where the camera and lens combination don't focus properly. The only thing is that DOF might hide this issue if only a minor lens adjustment is required. Therefore you might not see much difference in your photos focus if you only require a minor adjustment.

 

[elfroggio]

Also about the blur zone. Easier to describe with a diagram. The white are represents what is in focus, the grey is the blur zone and yellow is OOF. I believe the blur zone is shorter at f11 as opposed to F1.2 but I could be wrong. That was what I was trying to explain.

Quote from Rudy Wilson -- Canon (my emphasis):

The adjustments applied using this control are based on the depth-of-field you'd have at a lens's maximum aperture.

 

[guy schlacter]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

Then why is Canon saying ⅛ for depth of field if it is irrelevant? There is no "depth of focus" in that document. I'm saying that it does not exist. Why did Canon even provide that information?

@ 5 ft to target we get eight 0.015 increments. At 50 ft to target we get eight 1.89 increments. I'm not a technician but it seems logical 1.89 would be more forgiving to work than 0.015.

I get that if you move MFA +-1 the focus point shifts but it still can be within an area that was previously in focus. The DOF follows. Eventually as you keep increasing the MFA value the focus point will go into an area that was out of focus from the first reading. How else do you explain where Rudy says you may not see a change if up to 5 MFA moves?

If this is not correct please explain what Canon means by ⅛ of depth of focus and why are there so many different instructions of distance to target and why even Canon contradicts itself? There has to be a value because everything is math.

In my opinion you have gained proper understanding. See next post.

 

[guy schlacter]

This is how I see it based on doing this with rulers at one time. It is difficult to show this on a flat plane so this is a ruler on an angle.

The red lines represent the area that is was in focus originally at 0 MFA. The yellow areas are out of focus. Green is the focus point.

Column A is 0 MFA. B = 1 MFA shift. C= 2 MFA shifts. D = 3 MFA shifts.

The AF point in column D is still within the area that was in focus in column A - between the red lines.



According to Canon and the DOF chart the distance within the bracket that is in focus changes if you alter the distance to your target thus so do size of the increments.

I'm only basing this in what I think Canon is trying to tell me.

I like this post to better let people understand the shift.

However,I would make these changes;

1. Label the whole chart as "overhead view of distance" .Reverse the order of the columns.

2.Label each colum after reversing as 0mfa, +2 mfa,mfa, +4mfa, and+6mfa.(remember, each mfa click is 1/8 of in focus one one side of plane.

3. Label Yellow as oof . label height of box=2mfa clicks. Label green as center of current dof when shot.

4. move the red arrow up 3 rows., and label it desired subject distance. This then with the reversed could will show how adding mfa pushes the dof back and centers around where you place the AF point on subject.

5..Remove long red lines.

6..please repost.

 

[F3RSH]

DOF when applied to AFMA refers to Depth of Focus, not Depth of Field - see http://en.wikipedia.org/wiki/Depth_of_focus

So, those calculations of Depth of Field are not appropriate.

 

[guy schlacter]

DOF when applied to AFMA refers to Depth of Focus, not Depth of Field - see http://en.wikipedia.org/wiki/Depth_of_focus

So, those calculations of Depth of Field are not appropriate.

correct, hence the need to fix it to 2 mfa steps per row (block).

Per the second definition found using your link, of the near-symmetrical Depth of Focus around the plane of focus, there are 8 mfa clicks to Depth of Focus, so hence, each MFA click is 1/16 of the total Depth of Field.

 

[WilbaW]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

Where did you come up with that?

Right here.

Yes focus is done by a different sensor, but, the DOFs, focus or field, are impacted by the same physical rules and properties. The size of both DOFs will vary with subject distance.

You're agreeing with me but maybe you missed the "given", which means if you hold DO focus constant, what happens to the DO field as you vary the focus distance?

 

[WilbaW]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

Then why is Canon saying ⅛ for depth of field if it is irrelevant?

Of course the 1/8 is relevant. I'm saying the proportional variation with focus distance isn't, in the sense that whatever you are doing, it's always 1/8 of whatever DOF you have (according to Canon). It doesn't matter whether that's an inch or a foot, a click of MA is 1/8 of it.

There is no "depth of focus" in that document.

Correct, but AFAWK that's what's happening under the covers - it's how PD AF, BFCVs, and AF MA appear to work.

I'm saying that it does not exist.

Wow, that's a bold claim! Did you leave out a "not"?

Why did Canon even provide that information?

Because you can't see DO focus but you can see DO field, and 1/8 of one is 1/8 of the other.

@ 5 ft to target we get eight 0.015 increments. At 50 ft to target we get eight 1.89 increments. I'm not a technician but it seems logical 1.89 would be more forgiving to work than 0.015.

I think this might be the core of what I don't understand about what you're trying to work out - what does "forgiving" mean? What makes it relevant? When? Why? How? Etc?

I have a hunch you might be thinking like a foot is bigger than an inch so that's going to be easier to work with, but that foot of DOF is a lot further away from the camera than the inch of DOF, so does it make a significant difference? I'm not sure.

But does it matter? If you want focus closer or further away you can move it 1/8, 1/4, 3/8, 1/2... of the wide-open DOF, whatever/wherever the DOF is. Why does it have to be more complicated than that?

I get that if you move MFA +-1 the focus point shifts but it still can be within an area that was previously in focus. The DOF follows. Eventually as you keep increasing the MFA value the focus point will go into an area that was out of focus from the first reading. How else do you explain where Rudy says you may not see a change if up to 5 MFA moves?

And the problem is... what? I expect a "micro" adjustment to adjust with micro precision.

If this is not correct please explain what Canon means by ⅛ of depth of focus...

I think it is as simple as that - they claim 1 click is a 1/8 shift. If you want it shifted, shift it. What's the problem?

and why are there so many different instructions of distance to target and why even Canon contradicts itself?

This is photography, we have to make it complicated to have something to pontificate and bicker about.

There has to be a value because everything is math.

You don't need the maths to improve your AF accuracy with AF MA. Just try. If it didn't get better go back to zero or turn it off.

This discussion makes me think of a learner driver trying to decide which gear to use by comparing the gear ratios and working out the revs and speed... Just change up or down when you need to! You're just an operator, not the mechanical engineer designing the gearbox.

 

[WilbaW]

This is how I see it based on doing this with rulers at one time. It is difficult to show this on a flat plane so this is a ruler on an angle.

The red lines represent the area that is was in focus originally at 0 MFA. The yellow areas are out of focus. Green is the focus point.

Column A is 0 MFA. B = 1 MFA shift. C= 2 MFA shifts. D = 3 MFA shifts.

The AF point in column D is still within the area that was in focus in column A - between the red lines.



According to Canon and the DOF chart the distance within the bracket that is in focus changes if you alter the distance to your target thus so do size of the increments.

I'm only basing this in what I think Canon is trying to tell me.

Okay, sure, fine... but what's the point of being able to depict what's happening in this way? Why is it necessary and relevant? What does it achieve? What can you do with it?

 

[Zeee]

This is how I see it based on doing this with rulers at one time. It is difficult to show this on a flat plane so this is a ruler on an angle.

The red lines represent the area that is was in focus originally at 0 MFA. The yellow areas are out of focus. Green is the focus point.

Column A is 0 MFA. B = 1 MFA shift. C= 2 MFA shifts. D = 3 MFA shifts.

The AF point in column D is still within the area that was in focus in column A - between the red lines.



According to Canon and the DOF chart the distance within the bracket that is in focus changes if you alter the distance to your target thus so do size of the increments.

I'm only basing this in what I think Canon is trying to tell me.

I like this post to better let people understand the shift.

However,I would make these changes;

1. Label the whole chart as "overhead view of distance" .Reverse the order of the columns.

2.Label each colum after reversing as 0mfa, +2 mfa,mfa, +4mfa, and+6mfa.(remember, each mfa click is 1/8 of in focus one one side of plane.

3. Label Yellow as oof . label height of box=2mfa clicks. Label green as center of current dof when shot.

4. move the red arrow up 3 rows., and label it desired subject distance. This then with the reversed could will show how adding mfa pushes the dof back and centers around where you place the AF point on subject.

5..Remove long red lines.

6..please repost.

OK I'll work on it. When you think about this when shooting BIF, at distance and happen to nail the AF point in the eye the birds body and and wings (or most if them depending on conditions) is sharp. Most of the AF points are on the body when I shoot and I get tack sharp eyes. So there is a DOF range where everything is sharp. If you do one MFA shift the plane of focus does change but it may not effect the sharpness in within that area.

A +- 1 MFA shift may show a big change to someone else because it depends on how far apart the calibration is between the lens and the camera. If you had to MFA 7, 9 to more then yes something is out and it will effect the point you are expecting to be sharp with a small move.

 

[Zeee]

The ⅛ values change but as you get closer to the target they get smaller.

It's irrelevant. What AF in general and MA in particular is really working with is depth of FOCUS (at the sensor), not depth of field (perception of focus in an image). DO field depends on DO focus in the sense that a given DO focus will give different DO field at different focus distances. IOW, DO field can be all over the place while DO focus (the thing that matters, the thing that AF works with) remains constant.

Then why is Canon saying ⅛ for depth of field if it is irrelevant?

Of course the 1/8 is relevant. I'm saying the proportional variation with focus distance isn't, in the sense that whatever you are doing, it's always 1/8 of whatever DOF you have (according to Canon). It doesn't matter whether that's an inch or a foot, a click of MA is 1/8 of it.

There is no "depth of focus" in that document.

Correct, but AFAWK that's what's happening under the covers - it's how PD AF, BFCVs, and AF MA appear to work.

I'm saying that it does not exist.

Wow, that's a bold claim! Did you leave out a "not"?

Yes I let the "not" out. Sorry

Why did Canon even provide that information?

Because you can't see DO focus but you can see DO field, and 1/8 of one is 1/8 of the other.

@ 5 ft to target we get eight 0.015 increments. At 50 ft to target we get eight 1.89 increments. I'm not a technician but it seems logical 1.89 would be more forgiving to work than 0.015.

I think this might be the core of what I don't understand about what you're trying to work out - what does "forgiving" mean? What makes it relevant? When? Why? How? Etc?

I have a hunch you might be thinking like a foot is bigger than an inch so that's going to be easier to work with, but that foot of DOF is a lot further away from the camera than the inch of DOF, so does it make a significant difference? I'm not sure.

But does it matter? If you want focus closer or further away you can move it 1/8, 1/4, 3/8, 1/2... of the wide-open DOF, whatever/wherever the DOF is. Why does it have to be more complicated than that?

I foresee if I use your method @ a distance of 5 ft it may not even react with the defocusing step. If I do it at 50 it will be easier to do.

I get that if you move MFA +-1 the focus point shifts but it still can be within an area that was previously in focus. The DOF follows. Eventually as you keep increasing the MFA value the focus point will go into an area that was out of focus from the first reading. How else do you explain where Rudy says you may not see a change if up to 5 MFA moves?

And the problem is... what? I expect a "micro" adjustment to adjust with micro precision.

If this is not correct please explain what Canon means by ⅛ of depth of focus...

I think it is as simple as that - they claim 1 click is a 1/8 shift. If you want it shifted, shift it. What's the problem?

There isn't one. You said it was all about depth of focus and I was questioning why Canon says depth of field. I'm curios how the ⅛ increments are effected by distance to target.

and why are there so many different instructions of distance to target and why even Canon contradicts itself?

This is photography, we have to make it complicated to have something to pontificate and bicker about.

LOL

There has to be a value because everything is math.

You don't need the maths to improve your AF accuracy with AF MA. Just try. If it didn't get better go back to zero or turn it off.

This discussion makes me think of a learner driver trying to decide which gear to use by comparing the gear ratios and working out the revs and speed... Just change up or down when you need to! You're just an operator, not the mechanical engineer designing the gearbox.

That is true. Good point. The different suggested distances never made sense to me. It was like learning to drive and one person tells me to stop completely and another tells me it is a guide line and it is OK to coast and go. Obviously that second one was not by a professional driving school.

Like I siad. I have seen sensor discussions that have went to the molecular level because people are curious about how things work. In the long run as someone stated the only thing that matters is it ether helps or it does't but there is no harm in trying to figure out how something works. I never followed those sensor, read noise, etc conversations because after a while I'd get lost mostly because I never cared enough to learn more about it. Nothing I could do about it except switch manufacturers. This seems to have answered some questions I have had for a long time. It may have helped someone else - or not.

 

[WilbaW]

of MFA I always assumed a + or - move was a single fixed value if you did it at 2 ft or 1000 ft. Be it .0625, .125 or whatever number Canon used.

"A single fixed value" of focus distance? No! If that's what this is all about, just let it go, it's simply wrong.

That to me would be irrelevant.

Eh? I think you mean relevant.

It seemed logical.

Sure, but AF works with DO focus AFAWCT, so it's just wrong, sorry.

I'd still like to know what Rudy means by saying ⅛ of the Depth Of Field and how this effects MFA.

To the best of my understanding, what Rudy means is, a click of AF MA is applied mathematically as an increment of 1/8 of the DO focus (the context in which the AF system operates by converting focus errors at the sensor into lens drive commands), and you can see that change as a shift equivalent to 1/8 of the wide-open DO field. I also assume he's talking about focus distances up to 50f, where DOF is essentially symmetrical on both sides of the plane of focus, not further out towards hyperfocal.