Thursday, June 11, 2020

Hyperfocal Informed Bracketing Strategy

If you have been following my previous posts on using the Rule of Ten to inform your (non macro) focusing, you should now have a good understanding on how to:
  • calculate the hyperfocal using the Rule of Ten;
  • set a specific infinity blur and maximise the near depth of field for a single shot;
  • select the overlap blur using the equivalence rule;
  • carry our focus bracketing using the odds or evens rule.
In this post I'm introducing a pragmatic focus bracketing strategy, designed to be easy to use and robust enough to handle deep focus situations.

The Hyperfocal Informed Bracketing (HIB) strategy is based on knowing/calculating a single number. Namely the hyperfocal distance; either explicitly knowing it, estimating it from the DoF scale of your lens, or using the RoT to estimate it.

The HIB approach assumes you are focused on the nearest point of interest (POI) in your scene and you want the scene out to infinity to be in high quality focus.

In general, according to where your (nearest) POI is, relative to the hyperfocal, all you need to do to focus bracket for the near field, is to keep doubling the distance, until you are beyond H at which point you should select your final infinity shot.

If your POI is positioned beyond H, then all you need to do is take a single image at your selected infinity position, eg from, say, 2H to infinity.

If your POI is positioned between H/2 and H, then all you need to do is take the POI image and an infinity shot.

If your POI is positioned between H/4 and H/2, then all you need to do is take the POI image, refocus to double the POI and take a second shot, before adding a third infinity shot.

Finally, if your POI is less than H/4, then take three near field images at the POI, double the POI distance and four times the POI, ie double the second shot's distance, before taking a fourth infinity image.

Note that when the POI is less than H/4, the HIB strategy is strictly not fully optimum, but it is close enough That is pragmatism rather than mathematical purity.

To help you understand and practice HIB based focusing bracketing, I have created another eClass, which you can access on the right.

The following partial screen grab shows the HIB strategy in action. The (overlap) defocus CoC was put at 12 micron, ie double the 24mm RoT H. The POI is less than H/4, thus we take focus brackets at the POI, at twice the POI and at 4 times the POI, as well as an infinity shot at twice H.

I hope you have found this post of some value. As usual I welcome feedback of any kind.

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