Canon focus bracketing increments

Anton Largiader

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The bracket increments aren't described in the manual so it seemed easier just to test this for myself as I am trying to predict how many steps are needed to cover a certain object. I know I can just let 'er rip until the focus is clearly past the subject, but if I'm using flash the frames are 3 seconds apart (to give the flash time to recover) and I'd rather not monitor it for minutes on end.

With my EF100mm f/2.8 macro at f/11, set to a focus increment of 4, starting at MFD the first 30 steps covers 2cm, the next 30 covers about 2 more cm, and the next 30 covers about 3cm although the DOF is increasing enough that I can't be more specific. I determined this just by shooting down a ruler with zero at MFD, playing the frames back in-camera, scrolling through them and watching the filename and focal point change.

However, at f/2.8 and increment 4, 100 steps only covers 1.5cm. So clearly the camera's step size is adjusted to match the aperture. Canon wants to have perfectly sharp slices to use for the compositing.

I tried again at f/2.8 and increment 10, and it was 15, 30, 40, 50, 58, 66 steps to get to 1, 2, 3, 4, 5, and 6cm. This is pretty similar to what I got at f/11 and increment 4. But the camera complained that the DOF was too small - too much blur - to perform the composite.

I'm going to keep collecting data on this but it would be way nicer to crowdsource it. If you use this feature, please find time to set up a test and see how your lens responds to these adjustments.
 
The bracket increments aren't described in the manual so it seemed easier just to test this for myself as I am trying to predict how many steps are needed to cover a certain object. I know I can just let 'er rip until the focus is clearly past the subject, but if I'm using flash the frames are 3 seconds apart (to give the flash time to recover) and I'd rather not monitor it for minutes on end.

With my EF100mm f/2.8 macro at f/11, set to a focus increment of 4, starting at MFD the first 30 steps covers 2cm, the next 30 covers about 2 more cm, and the next 30 covers about 3cm although the DOF is increasing enough that I can't be more specific. I determined this just by shooting down a ruler with zero at MFD, playing the frames back in-camera, scrolling through them and watching the filename and focal point change.

However, at f/2.8 and increment 4, 100 steps only covers 1.5cm. So clearly the camera's step size is adjusted to match the aperture. Canon wants to have perfectly sharp slices to use for the compositing.

I tried again at f/2.8 and increment 10, and it was 15, 30, 40, 50, 58, 66 steps to get to 1, 2, 3, 4, 5, and 6cm. This is pretty similar to what I got at f/11 and increment 4. But the camera complained that the DOF was too small - too much blur - to perform the composite.

I'm going to keep collecting data on this but it would be way nicer to crowdsource it. If you use this feature, please find time to set up a test and see how your lens responds to these adjustments.
It depends at least in part on your aperture.
See: https://support.usa.canon.com/kb/index?page=content&id=ART178282
 
I wonder if the overall behavior varies much by camera. That was written for the R5.

Anyway, regarding the focus increment it's very unspecific:
Take some test shots to decide a suitable [Focus increment] setting.
 
This was the R3 (which can use flash for this; the R5 can't) but at some point I'll see how the R7 compares.

That Canon page doesn't really provide any numeric information. It would be great if they did quantify this increment but I'm assuming we will have to work it out ourselves.
 
This was the R3 (which can use flash for this; the R5 can't) but at some point I'll see how the R7 compares.

That Canon page doesn't really provide any numeric information. It would be great if they did quantify this increment but I'm assuming we will have to work it out ourselves.
As the aperture size plays a role, it still depends on the aperture setting for all the cameras because the aperture defines the depth of field (DOF). If you have a small DOF, typical with macro pictures, it will take more images to get the entire DOF range on an object.
 
I did a back to back comparison at increment 10:

f/2.8: 17, 17, 15, 10, 9, 8, 7, 6 for 1, 2, 3, 4, 5, 6, 7, 8 cm. Not exactly what I got before so something was a bit different in the setup. Maybe different parallax error with the ruler at a different angle.

f/8: 5, 5, 5, 4, 3, 3 to get to 1, 2, 3, 4, 5, 6 cm (didn't go to 8 but by 6cm the 8cm mark was practically in focus anyway, so you can see where this was going).

Both resulted in successful in-camera composites this time, but looking at the changes from one frame to the next it looks like this is about the biggest increment that gives enough DOF per slice. No big surprise there. Bottom line for me is that the whole 1-10 range is useful, especially if you stay within Canon's recommendation of f/5.6-f/11. No need (that I have yet seen) to be at the small end of the range.

This is all close up. As you can see the steps get longer as the DOF gets larger with distance. My macro stacks have tended to be fairly close up, so that's what I'm most interested in understanding for right now. But people who are shooting flowers and so forth at a slightly greater distance will need fewer steps to cover the same depth.

Next will be to see (just for the sake of knowing) if the step sizes are linear: is 4 four times the step of 1, is 10 twice the size of 5, etc. But that will not happen today. Anyone else want to do that?
 
I suspect Canon have coded for effective aperture, ie aperture and magnification (possibly pupillary magnification for the lens). Ie single shot depth of field, so each step always overlaps the next.

I am not sure it helps though. I guess the strategy is is as many steps as you can keep the camera steady for and sort it out in post.

I did some fungi and lichen shots using beanbag support recently and used the default 100 steps.

No point in 100 steps for a handheld shot of an insect, that is going to be best effort.

Anyway looking forward to others thoughts on this as I have not experimented much.
 
I had a similar conversation with a friend today in a videocall (he is in Holland). No conclusion was reached, but I find your results helpful.

Thank you
 
The bracket increments aren't described in the manual so it seemed easier just to test this for myself as I am trying to predict how many steps are needed to cover a certain object. I know I can just let 'er rip until the focus is clearly past the subject, but if I'm using flash the frames are 3 seconds apart (to give the flash time to recover) and I'd rather not monitor it for minutes on end.

With my EF100mm f/2.8 macro at f/11, set to a focus increment of 4, starting at MFD the first 30 steps covers 2cm, the next 30 covers about 2 more cm, and the next 30 covers about 3cm although the DOF is increasing enough that I can't be more specific. I determined this just by shooting down a ruler with zero at MFD, playing the frames back in-camera, scrolling through them and watching the filename and focal point change.

However, at f/2.8 and increment 4, 100 steps only covers 1.5cm. So clearly the camera's step size is adjusted to match the aperture. Canon wants to have perfectly sharp slices to use for the compositing.

I tried again at f/2.8 and increment 10, and it was 15, 30, 40, 50, 58, 66 steps to get to 1, 2, 3, 4, 5, and 6cm. This is pretty similar to what I got at f/11 and increment 4. But the camera complained that the DOF was too small - too much blur - to perform the composite.

I'm going to keep collecting data on this but it would be way nicer to crowdsource it. If you use this feature, please find time to set up a test and see how your lens responds to these adjustments.
Hi Anton,

This is an interesting experiment, can you specify the format size (FF or APS-C) and the magnification used in the experiment?
 
It was probably the FF R3.

As for magnification, it was the EF 100 usually starting at MFD, so I think that's 1:1?
 
Thanks Anton.

I did some sums assuming DoF is estimated by a circle of confussion of 0.03 mm, assuming a pupilary magnification of 1, and using your numbers in the first post, I get the following rough relationship:

Canon focus increment ____________ Step Size Factor
4 ______________________ 0.5
10 _____________________ 0.2

Where step size = StepSizeFactorXDOF.

For my WeMacro rail the tables they provide use a factor of 0.8 other people apparently recommend 0.7.

There is the obvious complication here that manification and probably pupilary magnification is changing on a large stack unlike the rail situation.

If these number are correct Canon are rather conservative on the step size.

Additionally these findings run counter to review descriptions on the web.

But I think a good way to view the step size is as a function of the step size factor (amount of DoF overlap).

Why Canon did not programme the feature like a macro rail control programme, where you set start, stop and say overlap factor I don't know, it would be much more useful.
 
It's all a bit over my head, but I have other macro stacks to shoot so please let me know what I can do to give better numbers.
 
It's all a bit over my head, but I have other macro stacks to shoot so please let me know what I can do to give better numbers.
I'll have to try some test why when I get a chance.

If you can repeat some tests with say focus increments of 1 and 7 to try and fill the relationship in.

If I can deduce the way it works, then some tables or plots could be generated to take out some of the guesswork.
 
Hi chaps,

I have done some tests on this and put these and a predictive Excel spreadsheet in a resource at https://focus-on-photography-forum.net/resources/canon-focus-bracketing.36/

The focus increment parameter can be understood as a depth of field overlap factor as I expected.

For example focus increment of 4 and f/5.6 10 steps gives:
  • about 4 mm of bracket depth at 1x.
  • about 8 mm of bracket depth at 0.5x

Alternatively 100 steps at f/5.6 and life size gives a stack depth of about 35 mm.
 
Not that I know the answer but is there a chance that you could use a flash that fires quicker?
Sure. Also, at low power my flash fires way faster than 3 seconds, but in the interest of not missing any after 40 or so flashes, I err on the safe side.
 
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