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.

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