Sunday, December 9, 2018

DoF Bar: Simple Focus Bracketing

In this post we will look at how DoF Bar can help you get perfect in-camera focus bracket sets. In the next post we will look at more advanced focus bracketing, but for now we will keep it simple. The DoF Bar settings for the simplest bracketing looks like this:


Here we see that the minimum focus has been set to the minimum DoF distance that we can achieve with the 24mm lens we are using at F/8, ie 390mm. We also have selected ‘Brackets to H’ in Pro Mode, as this will tell how many focus brackets we will need to take.

After composing the scene, in this case a really exciting image of my dinning table, we position the lens to as far as it will go to the macro end. Note that we can focus bracket in both directions, but in this post we will show the process near to far. The LV screen now looks like this:


DoF Bar is telling us that we will need at least 4 brackets to cover from where we are to the hyperfocal. As this will ‘only’ get of far DoF to the hyperfocal, we will usually take an additional image in the infinity focusing zone, ie H-4H, using the DoF Bar infinity blur feedback to inform our choice.

Note: the bracket to H information dynamically updates as you change focus.

We down take our first focus bracket, covering a DoF of 39-52cm, as shown below. DoF Bar also tells us that the lens defocus blur, at the DoFs, is 28microns.


As we haven’t moved to the next focus point yet, the top, showing the last image captured, mirrors the current focus conditions.

Let’s now focus away from the macro end and use the DoF Bar feedback to tell us when to stop. Remember we are looking to get the current near DoF as close as we can to the last image captured far DoF. To help us, DoF Bar flags up when we have over focused, ie the current near DoF would turn blue.


Here we see we have achieved the best conditions for the next bracket, with the current near DoF just short of the last far DoF. The current DoF now covers 52-80cm.

We now repeat the above until we are at the third focus bracket:


Here we see the current DoF covers 77cm to 1.71m. The final bracket, number 4, being this one:


Here we see that the current near DoF is 1.58m, ie less than the last far DoF of 1.71m, and that because we are focusing past the hyperfocal, our current far DoF is providing us with blur information, namely: we have an infinity defocus blur of 19microns, a diffraction blur of 10microns, giving a total blur of 21microns.

As we are seeking a near to infinity tack-sharp image, it would be prudent to take a final image to maximise the far field’s focus. DoF Bar helping getting us to this situation:


Here we see we have reduced the total blur to 14microns and the defocus and diffraction blurs are nearly the same.

We now have five focus brackets that need post processing. In this case, I also had Dual-ISO switched on, so the first step, after ingesting into Lightroom, was to process the Dual-ISOs arriving at these five images, clearly showing that, at F/8, we could not cover the full depth of field:

Macro End: 1st Image


2nd Image


3rd Image


4th Image


Infinity Focused Image

These images now need to be focused stacked, using your preferred approach. In this case I did a round trip to Helicon Focus, arriving at this ‘final’ image, ie I haven’t really bothered with any post processing beyond the basics.


In this post we have shown how DoF Bar can give you perfect focus brackets, near to far. A tack sharp image from the closest focus you can achieve on a 24mm at F/8, ie about 39cm, to a far infinity focus generating a total blur of 14microns, ie double the quality of an image taken at the hyperfocal.

In future posts I’ll provide further insights into DoF Bar.




Saturday, December 8, 2018

DoF Bar: Getting Started

In this post, and in future ones, I'll provide some examples of using the DoF Bar; but before doing so, let’s remind ourselves what DoF Bar looks like if we are ‘simply’ using it to provide DoF feedback associated with the single image we are attempting to take.


The DoF Bar menu looks like this. Here, in this example, 'Show Bar' is ON, if it was 'OFF', DoF Bar would be hidden in LV; The minimum focus is set at 700mm; Bracketing of set to OFF; and Pro Mode (not discussed in this post) is set to Blurs. Finally, the the dynamic bar option is set to DoF (my preferred option).

DoF Bar provides focus information in two formats. First, the near and far depth of field distances. Secondly, infomation about the blurs at the DoFs. There are three types of blur that DoF Bar reports:

  • Lens generated defocus blur (f)
  • Aperture generated diffraction blur (d)
  • Total blur calculated from the RMS of the f and d above (t)
In addition, DoF Bar provides additional blur information associated with 'infinity focusing', ie focusing beyond H and less than the Canon reported infinity. When infinity focusing, the far (sic) DoF blur becomes less than that which is active when you are focusing at less than H.

Thus, if you see an ‘i’ in front an ‘f’, ie ‘if’, you know that blur refers to the infinity state.

To illustrate how to use DoF Bar, the use case we will look at in this post, is how to set focus for maximum depth of field and (sic) best image quality.

First, as we are seeking best image quality we need to be sensitive to diffraction, so we will switch that on in the ML Focus Menu. In this case, we will use the 'normally accepted' full frame total blur criterion of 30microns and we will switch on diffraction aware.
 


We also note that an lens’s overall quality varies as we increase aperture; and many photographers recognise there is a sweet spot about (sic) a couple of stops down from the lens’s widest aperture. For example see https://www.cambridgeincolour.com/tutorials/lens-quality-mtf-resolution.htm.

To illustrate how we may use DoF Bar, let’s look at a 24mm lens, set to its widest aperture, and focused short of its hyperfocal (H). The Live View will look something like this:
 


Here we see we are at an aperture of F/5.6 and that DoF Bar is reporting a near DoF distance of 69cm with a (de)focus blur of 29microns, and a far DoF distance of 1.06m with a total blur of 30microns, as one would expect, as we have set 30microns as our criterion in ML. ML is also reporting (bottom bar) that the focus is at 84cm. 


Note that if we are focused short of the hyperfocal distance, the end of the green bar, then, by definition, the blurs at the near and far DoFs are the same. Thus although the near DoF above is reporting 29microns of defocus blur, this is the same at the far DoF. Likewise, the total blur of 30microns at the far DoF, is the same at the near DoF.

Let’s now refocus towards infinity and stop when the far DoF just goes past the hyperfocal.

BTW the hyperfocal and other info may be seen in the ML Focus menu, eg: ML info in menu we see reported that, at this aperture, the diffraction blur is 7microns; and that the hyperfocal is at 3.59m: 



After refocusing the LV now looks like this:
 


Now we see the DoF Bar format has changed, with two additional bars coming into play. The left hand one being a visual aid, set by the user as the min focus, ie 700mm in this case. The right had bar is sub-divided into three zones, covering H-2H, 2H-3H and 3H-4H. In this example the near DoF has moved to 1.35m, the far DoF at 4.97m and the focus at 2.11m. The blurs, of course, have not changed.
 

Lets now continue focusing, to just beyond H and shut our aperture down to a more sensible F/11.
 


Here we see at a focus of 3.86m, the DoF Bar is report the near DoF distance as 1.34m, with a focus blur of 26microns now as we have changed the aperture, and, as we are at/beyond the hyperfocal, DoF Bar now switches from showing the far DoF distance, which is infinity, to showing us infinity blur information, ie the blur at infinity. The additional information we see is that the infinity focus blur has dropped to 14microns, the diffraction is at 15microns and the total blur is 20microns. Thus the far quality of focus is now better than at the near DoF, where the total is, of course, still 30microns.

We also see the text colour has changed from green (not shown) to yellow, warning us that the diffraction blur is larger than the defocus blur.

Without DoF Bar we simply would not be aware of this additional focusing information; as once we have gone past the hyperfocal distance, ML provides us no additional information, other than the focus distance. But we know that, as our focus approaches infinity, the defocus blur of the lens reduces to zero, at infinity. That is, once past the hyperfocal distance, the focus quality between the focus point and infinity, keeps getting better.

But, as we know, if we focus at infinity, the near DoF is at the hyperfocal distance. So, once we have achieved the required focus quality, there is little point keep focusing towards infinity, as you are losing near DoF. Or put another way, the near DoF, from the hyperfocal distance (H) to infinity, reduces from H/2 to H: thus if your near DoF needs are meet by a near DoF of H, then you can safely focus towards or ‘at’ infinity.

But what is you need to maximise the near depth of field? What should you do?

Most photographer will approach the above by decreasing the size of the aperture, knowing that doing this will, and ignoring diffraction, increase their DoF, ie make their near DoF as close to the camera as possible. So let’s do that. Let’s leave focus where we are and simply keep shutting the aperture down.

BTW if the infinity blur information turns red, then we are focusing beyond 4*H and are likely seeking defocus blurs smaller than is sensible with the sensor, ie less than two sensor wide.
 


The near DoF is now at 1.23m and the defocs blur at the near DoF is 21microns. We also note the diffraction blur is 21microns, the defocus (infinity) blur is 10microns and the total blur is now 23microns.

But, as an experiment, let’s carry on closing down the aperture to its smallest, eg F/19 and F/22. We now see this on the LV screen:
 



At F/22, there is no solution, and at F/19 the near DoF is at 1.39 at a defocus blur of 14microns, ie we have lost depth of field because, of course, diffraction is beating us. Also the total infinity blur is now up to 27microns. Remember that ‘focus quality’ is a root mean square addition of the lens defocus blur and diffraction blur.

So it looks like that F/11 was best for gaining the most near DoF and getting the infinity blur as low as possible.
 

Thus, at a focus distance of 5.24m and at an aperture of F/11, the near DoF, which meets our ML set criterion, is 1.47m, and the overall blur at infinity is 18microns. Knowing that ‘best’ lens quality will be found at around F/11, means this is a good place to finish focusing.

Hopefully this quick introduction to DoF Bar has provided sufficient information to allow others to experiment with focusing by blurs. In future posts I’ll provide insight into one of the main features of DoF Bar, namely focus bracketing.

Tuesday, November 27, 2018

DoF Bar: Background

In past posts I’ve talked about focus and introduced two tools that help you make informed decisions about focusing, namely: The Rule of Ten (ROT) and the (Canon EOS only) Depth of Field Bar (DoF Bar).

In this post, and a subsequent one (Part 2), I hope to persuade readers why using these two tools, especially the camera-agnostic ROT, is a good idea.

My reason for the tutorial is simple: some have told me they don’t understand what I’ve previously written!

Now that could be 100% down to me and how I write; or, as I prefer to believe, a bit of me and bit of a lack of knowledge in the reader about using blurs to optimise focus.

What follows in this post, ie Part 1, is a reminder on the basics of focus, which is essential to know if you are going to get the best out of the two tools mentioned above.

So what is Focus?

At its simplest focus is subjective and related to the viewing conditions. For example, one person, with a visual acuity of X, looks at a print and sees everything ‘in focus’; whereas, another person, with better eye sight, looking at the same image might see a sight softness in places. Then both look at the same image on a Facebook page and, magically, the image is in focus everywhere, for both of them.

As photographers have considered focus for over a hundred years, we now have ‘accepted standards’ when we talk of ‘sharpness’ or ‘focus’. One of the recognised ways of discussing depth of field assumes (mixing units) an enlargement to 8 x 10 inches, at a viewing distance of 10 inches, and a normal visual acuity of about 5 (black and white) line pairs per mm (lp/mm) at that viewing distance.

We then use this 5 lp/mm, or 0.2mm for 1 lp, on a print, to estimate an acceptable blur, which is often called the circle of confusion (CoC), on the sensor. A recognised estimate being:



If we now assume a full frame sensor, ie 36mm x 24mm, the above becomes:



The above resulting in the oft reported CoC of 29 microns for a full frame camera.

As we can see from the above, if the viewer was not looking at an 8 x 10 inch print at 10 inches, then the CoC would change. For example, viewing a large bill board at 20 feet away vs viewing a Facebook image on a phone screen.

This leads to the first guidance on focusing that I would offer, namely, unless you really know the final viewing size and conditions, stick with the standard CoC guidance. For shear convivence, I personally use 30 microns on a full frame and 20 microns on a crop sensor, as my base CoCs: that is acceptable focus quality; as they are also easy numbers to remember.

Rather than keep saying CoC , I find it more convenient to call the CoC a blur; and recognise that the total blur is made of two main components: the lens defocus blur and the diffraction blur; and without proof, it is usual to discuss these three blurs in the following way:



Lenses, of course, are complex mechanisms and far too complex to handle without a great deal of mathematics and computer modelling. Thus, for convenience, photographers resort to making use of a simple model of the lens, that allows us to estimate the focus field in front of and behind the point of focus. These simple equations are really only suited for non-macro photography, eg landscape photography.

Before looking at a little more maths, let’s look at a what a typical lens defocus field looks like. The horizontal axis is the distance from the lens (ie approximately the camera) and the vertical axis measures the defocus blur, with the defocus blur criterion, in this plot, being set at 30 microns.



Here we see the classical shape of the defocus blur. The in-focus portion is where the blur is less than our 30 microns. These two distances, near and far, are thus our near and far depths of field.

We also begin to see that, the focus in front of the point of focus, does not equal the focus behind the point of focus. The two extremes being:

· As the point of focus approaches the lens minimum, ie macro shooting, the focus in front and behind collapses towards being the same.

· There is a distance where the far depth of field is the same as our criterion (30 microns here) and, at this point, the near depth of field is half of the focus. This point is called the hyperfocal distance or H.

Once again, for pragmatic reasons, and assuming we are not doing macro photography, we can make further simplifying assumptions that lead to the hyperfocal distance being estimated from the following:



Where f is the focal length and N the aperture number; and where the defocus blur can be found from:



Now the diffraction blur, in microns, can be estimated from:



Where k is 1.34, for normal visible, ie not IR, photography: thus, at an aperture of F/10, the diffraction blur may be estimated at just over 13 microns.

BTW, F/8-F/11 is recognised a sweet spot for a lens in general, ie overall image capture quality.

The above simple equations now give us everything we need to estimate H and account for diffraction; and if we focus at H we get the following result, with an infinity blur of the defocus criterion:



As an example, let’s take our 30mm lens at F/10 and work out H to meet a total (sic) blur of 30 microns. First, the diffraction blur we know is 13.4 microns. Plugging this into the above gives the following:



Which equals 26.8 microns, which we now plug into the equation for H, converting 26.8 microns into mm, to get:



Which gives a diffraction informed hyperfocal distance of 3.35m, which may be compared to the hyperfocal if we did not account for diffraction, which would have been 3m, ie:



Using the ROT to make it simple

The above, although a simplification, is still not that easy to calculate in your head, which is why most revert to Apps or look-up tables, or guess the hyperfocal.

We can, however, greatly simply things by using the Rule of 10, which simply says set the defocus blur to the focal length (f) in microns, ie:



And if we set N to F/10, we have a very simple way of estimating H, in meters, in our heads, ie HROT = f/10.

Thus, in our example above, ie a 30mm lens used at F/10, using the ROT we note that this will be at a defocus blur of 30 microns, ie focal length in microns, H will be 3m.

But let’s say we wish to achieve a higher quality print with a defocus blur, say, of 15 microns; then, using our ROT all we need to do is factor the ROT H by a factor of 2, ie 30/15. Thus, if we focus at 6m, this becomes our new H, but with a defocus blur criterion now of 15 microns.

But what if we weren’t using a 30mm lens? Once again, the ROT approach allows us to quickly calculate where we should focus. As an example, let’s choose a 15mm lens set at F/10 and seek out H at a defocus blur criterion of 30 microns.

Using the ROT methodology, we would focus at 15/10 = 1.5m, but of course this means our defocus blur is the focal length in microns, ie 15 microns, whereas we are seeking H at 30 microns, which is twice the ROT number. So all we need do is focus at half of H, or 0.75m.

Once you get the ROT approach in your head, it is a very simple matter to estimate defocus based hyperfocal distance, H.

As a recap, here is the ROT:



But why are blurs and H so important?

Knowing your defocus blur, and thus H, means you are in full control of focusing information. Also, by being sensible with aperture, ie setting it to 10 or there about, means you are not letting diffraction beat you. Thus, pragmatically, at F/10, you can ignore diffraction and simply use the ROT-informed H. As shown above, if we ignore diffraction the total blur is only made up of the defocus blur, say, at 30 microns, and if we include F/10 based diffraction, the defocus blur only reduces to about 27 microns.

Thus we can safety use the ROT approach without worrying about diffraction, as long as we focus a little beyond H. Certainly 2*H, ie a defocus blur of 15 microns for a 30mm lens using the ROT approach, is well beyond a ‘little beyond H’.

In general, H based focusing looks like this:


Here we see if you focus as H, your near depth of field will be H/2; and if that is not sufficient, all you need to do is refocus at the odd fractions of H, ie H/3, H/5 etc until you have covered your required depth of field needs. Your near and far depths of field at these new points of focus simply become the even fractions either side of the odd fraction. Thus if you focus at H/9, the near and far depths of field will be at H/10 and H/8.

In addition, as you focus towards infinity and away from H, you can simply dial in the infinity blur that you wish to use. Thus at 2H, the infinity blur will be half of that at H.

BTW the above also shows us that the often repeated advice that focus is one third in front and two thirds behind the point of focus, is only true when the focus is H/3.

Pragmatically, five focus brackets is most probably a sensible lower limit, which we now know will extend your near depth of field from H/2, that a single image gives you, to H/10.

Bottom line

In this post we have reminded ourselves that focus is really the ‘zone of acceptable out of focusness’, based on reasonable assumptions about viewing distance and eyesight. We also recognise that the total blurriness in an image is made up of the lens out of focus and a contribution from diffraction.

In order for diffraction not to become an issue, and to maximise image quality, F/10 is a good place to be capturing images.

Also, by using F/10, we can make use of a very simple rule (Rule of 10) to find the hyperfocal distance, H. That is H, in meters, is the focal length in mm divided by 10 (or in general N), generating an infinity defocus blur of the focal length in microns.

Finally, knowing this focal length informed H, we can estimate any near and far depth of field; and undertake focus bracketing, ie by focusing at the odd fractional parts of H.

In the next post, now that we know all about blurs and the power of knowing the hyperfocal, I’ll discuss how to make use of the Depth of Field Bar that runs under Magic Lantern.



Friday, November 23, 2018

Focusing Update




 This is a revised post as DoF Bar had a minor program error that resulted in the DoFs being mis-reported. The link on the right has been updated.

If you have been following my recent posts you will be aware that I have been revisiting focusing; which has resulted in two ‘new’ tools.


First, the system-agnostic, ie it works for all cameras, ‘Rule of 10 (ROT)’, which I subsequently found to be an old idea from the 19th Century, but I believe I have given it a 21st Century life. The ROT allows you to calculate the hyperfocal distance, infinity focusing distance and focus stacking distances, all in your head.


Secondly, for EOS camera users only, the Magic Lantern based Depth of Field Bar (DoF Bar) that provides in-camera information to inform your infinity focusing, ie focusing between the hyperfocal distance and ‘infinity’, and focus bracketing.


Both these tools allow you to achieve optimum focus without reference to a single App or look-up table.


In this post, I’m updating the DoF Bar, to address a couple of weaknesses in the initial release and introduce additional functionality to help with bracketing from an infinity focused position, ie where your first image in a bracket sequence is focused at greater than the hyperfocal but less than four times the hyperfocal.


The DoF Bar script may be downloaded from the right hand link; which will always give you access to the latest version of DoF Bar.


For those that wish to read more about DoF Bar, here is the ‘User Guide’.



DOF Bar User Guide


DoF Bar is principally targeted at those that wish to obtain 'tack sharp' images from infinity to a near-field point of interest, eg landscape and cityscape photographers.



It can, however, also be useful to those who simply wish to know more about depth of field (DoF), especially when focusing beyond the hyperfocal, but short of 'infinity'.



It goes without saying that DoF Bar only works in a Canon EOS camera with Magic Lantern, in Live View and with lenses that report focus distance, focal length and aperture. DoF Bar checks for this and will only show itself if it is able to so do.



When bracketing, DoF Bar is best being used at the wider end, say 50mm or wider. However, it can be used with longer lenses, but be warned: focus bracketing can become tiresome at long focal lengths ;-)


For example, using the Rule of 10, a 100mm lens at F/10, using an infinity defocus blur of the FL in microns, will have a hyperfocal distance (H) of about 10m = FL/10. If we now bring this down from 100 microns to 10 microns, H corresponding moves to 100m, ie 10 x the H at 100 microns. 


Thus the number of focus brackets to cover from 10m, say, to infinity will be 5, using a 10 micron criterion as the overlap, ie H/2X = 100/(2*10).


Whereas, if we wished to cover from 1m to infinity, we would need 50 brackets (=100/(2*1)), that is an additional 45 to cover from 10m to 1m!!! This emphasises the non-linearity of focus around the hyperfocal.



As a further illustration of the above, let’s assume we relax things and use an ‘OK’ CoC of 30 microns with our 100m lens, ie H becomes one third of the H required to achieve a 10 micron CoC, ie 100m/3 = 33.3m. If we still wish to cover a focus range of 1m to infinity (at a CoC of 30 microns), the number of brackets is ‘reduced’ to about 17, ie  H/2X = 33.3/(2*1).



In other words, don’t try and focus bracket with long lenses ;-)



The current focus is always shown by ML on the ML bottom bar and DoF Bar assumes you have set metric units in ML. DoF Bar will switch off ML shown DoFs, as DoF Bar shows this info.



DoF Bar menu appears under the ML Focus menu. All DoF Bar menu states are remembered at camera close, so you don't have to keep entering your settings once you have arrived at your preferred configuration.



DoF Bar uses the ML set Circle of Confusion (CoC), ie the total (sic) blur criterion at the hyperfocal. The total_blur being calculated from SQRT(lens_defocus_blur^2 + diffraction_blur^2). With diffraction blur linearly varying with aperture alone, ie a lens at F/8 has twice the diffraction blur of one at F/4.



If ML diffraction aware is set to off, the ML (total) CoC is, obviously, only based on lens defocus blur. If ML diffraction aware is on, then the (lens defocus based) hyperfocal (H) is calculated by ML after diffraction is accounted for, ie lens_defocus_blur = SQRT(total_blur^2 - diffraction_blur^2).



If diffraction is too high, ie diffraction blur >= total blur, the near and far DoFs will collapse to the focus point.



So, be warned: according to your ML set CoC, apertures much beyond, say, F/16, on a full frame (less than this on a crop sensor camera), mean you begin to lose DoF because of diffraction.



Thus, because of diffraction, many photographers try and capture images around F/8 to F/11, as pushing things towards F/16, whilst resulting in larger DoF, may also introduce loss of image quality, eg achievable lp/mm, because of other factors related to lens design. For example see: https://www.cambridgeincolour.com/tutorials/lens-quality-mtf-resolution.htm



You can switch DoF Bar on and off, ie hide it in LV, via the script's menu.



NOTE: If DoF Bar 'disappears', for whatever reason, then simply carry out a half-shutter press to return DoF Bar to the LV screen.



The bar is segregated into three sub-bars, each with different scaling; in order to maximise the info presented in the bar.



The left hand (white) sub-bar covers distances from zero (an estimate of the camera's sensor plane) to a minimum focus distance that you set (this does not have to be the actual lens minimum). This min focus is only a visualisation aid and is user set in the script’s menu, and it can be zero, ie no white bar to the left of the green bar.



Hint: one way to use this user controlled feature is to move your lens to the macro end until the near depth of field doesn't change. You may consider this to be your minimum focus and set this in the menu ;-)



The middle (green) sub-bar covers distances from your set minimum focus to the (diffraction aware) ML calculated hyperfocal distance (H). Thus, if the minimum focus is set to zero, the green bar will go from zero (the camera) to H.



The right hand sub-bar (with three zones, white/black/white) covers distances from [H to 2H] [2H to 3H] [3H to 4H]. This right hand zone is used when ‘infinity focusing’, ie beyond the ML calculated H.



Note that infinity blurs go in proportion to multiples of H. Thus if focused at 3H, your infinity blur will be that at H (the defocus blur as set/calculated by ML) divided by 3, ie a third of that at H.



As defocus blurs less than twice the sensor pitch are rather meaningless, as you need at least two pixels to resolve a line pair; DoF Blur uses H/4 as a pragmatic limit; knowing that we are using DoF Bar with Canon EOS sensors.



In Pro mode (see below) DoF Bar will only allow you to set infinity blurs between H and 4H. For example, on a 5D3 twice the sensor pitch is about 13 microns. Whereas most will set the ML set (full frame) blur to, say, 30 microns, as this is recognised as an OK criterion to use for 'normal' viewing of an image. The smallest (DoF Bar allowed) infinity blur in this case is thus 30/4, which is about 8 microns, ie slightly less than, but close to, the 'sensible' (two pixel) sensor limit.



Of course, for web-based digital viewing, blurs can be more than for close scrutiny print viewing. But, unless you know the final presentation mode and what blur you wish to achieve, it is best to seek infinity blurs between 30 to, say, 12 on a full frame, and, say, 20 to, say, 8 on a crop sensor. DoF Bar, of course, helps you by indicating the sweet spot, ie green and not red blurs.



The left hand of the bar will always be the lesser of the current near DoF and the near DoF of the last image taken.



If DoF mode is selected, the right hand will be at H if both the current and last far DoFs are greater than H; or at the greatest of last far DoF and current far DoF. If Hyperfocal mode selected, the right hand will always be at H if the current far DoF is less than H. 


These two dynamic modes become useful as you focus towards the macro end, so the advice is have the Dynamic Bar switched on. Just try it ;-)



There are three 'info areas’ above the bar.



The left hand one always shows the current near DoF distance, as reported by ML.



The right hand info area shows the current (ML reported) far DoF distance, if the focus distance is less than H. If the focus is greater than the ML reported H, this info area shows the infinity blur (in microns) at the current focus distance, which will be between the ML calculated hyperfocal (defocus) blur (ie ML CoC if diffraction aware is off) and zero if focused at infinity. Blurs of zero, of course, only occur at the point of focus.



The third info area only appears in Pro mode and shows the current ML calculated defocus blur (diffraction aware sensitive) and the infinity blur that is currently set. The infinity blur is set by taking an image between H and 4H.


This infinity blur will then remain in force UNTIL the lens state changes, ie aperture or focal length, or you change the ML set total CoC. If you change lens state, you will need to take another image between H and 4*H to reset the infinity blur that is ‘in play’.


Or, put another way, if you wish to reset the infinity blur at anytime, all you need do is change lens state and (sic) take an image between H and 4H.



In its non-bracketing mode, the Focus Bar shows the three main focusing fiducial markers/semi-dots below the bar. Red is the focus point and the left and right white semi-dots show the near and far DoFs as calculated by ML.



As soon as you take your first image (anywhere), if bracketing mode is set to off (script’s menu), all you will see are these dots mirrored on top of the bar and these will remain mirrored as you refocus.



However, if you are in bracketing mode, once an image has been captured, the upper dots will now be (and remain) positioned at the last captured image’s points of interest, ie near-DoF, focus point and far DoF.



The current focus white, near or far, DoF semi-dots will turn blue when you have opened a 'focus gap' between your last image taken and the current focus.



You can now use these top and bottom dots to inform your focus bracketing, ie refocus until the lower far DoF is just greater that the upper near DoF (of the last image), ie white and not blue. Thus, in (non Pro) bracketing mode, you can focus bracket from anywhere at anytime; thus ensuring your current focus is focus bracketed to you last image.



If you are focusing at the Canon/ML indicated infinity, the lower dots will turn black as you are in a potential over focusing state, according to the lens you are using.



Note: the (non-Pro) DoF dots work in any focusing direction, from near to far as well as far to near.



Due to the coarseness of the Canon distance reporting, you may not always be able to position your focus to exactly where you want: so do the best you can.



If you are in Pro Mode (set in the script’s menu) two additional upper and lower (magenta) semi-dots will appear. The upper magenta semi-dot shows the near DoF of the first captured image you took between H and 4H after camera switch or after a lens state change. The infinity blur at that point is used to calculate the (infinity blur based) near DoF. The lower magenta semi-dot shows the (infinity blur based) far DoF at the current focus, once again using the infinity blur criterion established when you captured your image between H and 4H.



As you refocus, to achieve the perfect focus bracket, the lower magenta semi-dot will change from magenta to blue when you have opened up a focus gap.



Note: in Pro mode you should only focus bracket from far to near.



The infinity blur criterion will remain fixed until you change the focal length, aperture or the ML set hyperfocal by changing the CoC in ML; and take a new image between H and 4H.



Thus you can focus bracket at, say, image sequences less than H, BUT, in Pro mode you must have taken your first image (after camera switch on or after a lens state change) between H and less than 4H, and, of course, focus stack from far to near.



Having established your infinity blur, all you need to do on subsequent focus brackets is to ensure the two magenta dots (top = last near DoF and bottom = current far DoF based on infinity blur) are as close together as possible (that is as close as the Canon focus reporting allows); and both are magenta, ie if the lower turns blue you need to refocus or accept where you are if the current far (white) DoF marker is still white, meaning that you are between the ML set/calculated blur and the infinity blur DoFs.



If both magenta and white far DoFs of the current focus are blue, you will have a (real) focus gap that needs fixing.



You can keep using the magenta dots for images captured below H, but as soon as you do a lens state change and take an image between H and 4H, you will establish a new infinity blur criterion.



In Pro mode the middle Info area reminds you of the blurs that are being used to calculate the white and magenta DoF dots, ie ML set (at the OK focus quality level) and your currently active infinity blur (high quality)



If you change the focal length, the aperture or the ML set CoC; the DoF Bar will reset to its ‘camera on’ state, eg the upper dots will disappear, until you take another image. Plus, in Pro mode, the infinity blur based info will be reset and you will need to take an image between H and 4H to establish a new (Pro mode) infinity blur.



Finally, you can use DoF Bar as an armchair visualization tool. For instance, to inform you how DoF changes as you adjust aperture, eg by looking at the changing DoFs until they are at their maximum and suit your needs.



Caveat emptor: remember that the equations that ML and DoF Bar use are good approximations away from the macro end, based on mathematically simplifying the lens. In other words, don't use DoF Bar with a macro lens!



Finally, here is a screen capture showing the full richness of DoF Bar.




As usual I welcome feedback on this post, especially related to making DoF Bar even better.