Focus Bracketing R6

Started 2 months ago | Questions
Phylloxera Regular Member • Posts: 148
Focus Bracketing R6

Simplifying macro stacking by focus bracketing was one of my reasons to buy an R6.

First problem: setting the focus increment FI). The distance of the steps are arbitrary units on a scale 1-10 and the value has to be guessed more or less because it is  depending heavily on the focus distance and the focal length of the lens.

Here some crude values obtained with the EF 100 2.8 Macro. CR3 files were developed and stacked with Helicon focus 7 without any problem.

Focus distance  FI setting   Actual increment per step

0.3 m (1:1)               10                0.6 mm

0.5 m (1:4)               10                3.5 mm

1.5 m (1:10)               4                15  mm

If someone has experiences with this lens or other ones I would be grateful to get more values and comments This might save a lot of testing time for all beginners in this technique  ...

ANSWER:
Canon EOS R6
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JustUs7 Senior Member • Posts: 2,664
Re: Focus Bracketing R6
1

The increments are more about focal plane overlap than actual measurements. 1 meaning significant overlap of the depth of field requiring more images. 10 meaning almost no overlap.

The camera calculates the depth of field based on aperture, focal length, and distance from the initial focus point. So, shooting at 24mm at f/8 using an increment of 10 and an initial focal point 5 ft away might only require 2 or 3 images to cover a focus bracket to infinity. While focusing at the minimum focus distance using a 100mm lens at f/2.8 using and increment of 1 could take hundreds.

I generally leave it at 4, which I guesstimate to be about 60% overlap then base my number of images using a depth of field calculator. If the calculator says my depth of field is 0.2 inches, and I need to cover a 3 inch subject, I’ll take images and stack as many as I need to cover the subject. My math says 40, but I’ll review and leave off wherever I no longer need sharp images. So I might take 60 just to be safe and delete what I don’t use.

For the 3 inch subject with a 4 overlap factor, my math goes something like 0.2 * (1 - 0.6) = 0.08 inches. I have 0.08 inches that doesn’t get covered by overlap. 3 / 0.08 = 37.5 images. Then I add a few for a fudge factor.  With a lower number, I need more images.  With a higher number, less.

Remember too that as your focus point moves through the scene, the distance from the sensor becomes greater and therefore depth of field increases. This means that regardless of number (1-10), the focus increment will be variable (increasing) as it moves through the scene. There won’t be a fixed distance to assign.

Or if I want to go to infinity, I’ll put in 999 images and the camera stops when focus reaches infinity.

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OP Phylloxera Regular Member • Posts: 148
Re: Focus Bracketing R6

Thank you very much for this valuable information!

Now I understand why the differences between FI= 4 and FI=10 were always far less than I supposed (basing on wrong assumptions).

For the tests with the EF 100 I used F 2.8 to get the best focus points - usually I would use 5.6 to get maximal resolution. If I understand the algorithm correctly, in this case the camera would calculate larger steps for a given focus increment?

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JustUs7 Senior Member • Posts: 2,664
Re: Focus Bracketing R6

Phylloxera wrote:

Thank you very much for this valuable information!

Now I understand why the differences between FI= 4 and FI=10 were always far less than I supposed (basing on wrong assumptions).

For the tests with the EF 100 I used F 2.8 to get the best focus points - usually I would use 5.6 to get maximal resolution. If I understand the algorithm correctly, in this case the camera would calculate larger steps for a given focus increment?

Larger than f/2.8, yes.  And 1 would be the most overlap and require the highest number of images while 10 would be the least overlap and require the fewest images.

 JustUs7's gear list:JustUs7's gear list
Canon EOS 1000D Canon EOS Rebel SL1 Canon EOS RP Canon EOS M6 II Canon EF 75-300mm f/4.0-5.6 III +7 more
Karl_Guttag Senior Member • Posts: 1,140
Re: Focus Bracketing R6
1

Phylloxera wrote:

Simplifying macro stacking by focus bracketing was one of my reasons to buy an R6.

First problem: setting the focus increment FI). The distance of the steps are arbitrary units on a scale 1-10 and the value has to be guessed more or less because it is depending heavily on the focus distance and the focal length of the lens.

Here some crude values obtained with the EF 100 2.8 Macro. CR3 files were developed and stacked with Helicon focus 7 without any problem.

Focus distance FI setting Actual increment per step

0.3 m (1:1) 10 0.6 mm

0.5 m (1:4) 10 3.5 mm

1.5 m (1:10) 4 15 mm

If someone has experiences with this lens or other ones I would be grateful to get more values and comments This might save a lot of testing time for all beginners in this technique ...

I ran a few experiments to "decode" the algorithm using the RF100f2.8 Macro. In this experiment, I shot a ruler and then went through the photos to see how the focus moved (how many shots per 10mm increment in focus).

https://www.dpreview.com/forums/post/65446398

It seems the camera is computing a formula based on the lens, f-number, and focus distance. I have verified a few times that the focus stepping is inversely proportional to the f-number. So if you say double the f-number, the number of focus steps is half for the same range.

One other thing I noted with the RF100 Macro is that there is considerable "breathing" when shooting a focus stack starting from minimum focus distance. See my 3rd post on that topic: https://www.dpreview.com/forums/post/65446765

From some of my earlier experiments, the default F.I. of 4 seems to be about right. Going with an index of much more than 4 will cause some visible focus "wobbling" (blurring) between images. Smaller indexes will probably be better, but you have many more images to combine, and it takes longer to shoot (more time for something to move).

I expect there will be some similar issues concerning f-number if the lighting is not an issue. At higher f-numbers, there are fewer images to blend, but there is more of a focus difference between shots at the same F.I. number.

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OP Phylloxera Regular Member • Posts: 148
Re: Focus Bracketing R6

I'm still wondering how I could miss your elaborate measurements two weeks ago! My crude ruler tests with the EF 100/2.8 gave similar results.  I'll add a foto with additial remarks to your thread to keep additional informations together. Thank you again!

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