Thursday, February 21, 2019

More Focusing & Stacking with CHDK

I've now updated the CHDK Landscape Focus Bracketing script and thought it worthwhile reminding readers what this script can do.

Being a CHDK Lua script, it runs on Canon Powershots. I've tested it on my S95, my G7X and my G1X.

In this post I show an example of what the script can do on a G7X, which has a minimum focus of 20cm.

The script can now work in a near full auto mode, using the Mac2Inf focus bracketing option. If this mode is selected, the script will automatically position the lens at the camera's minimum focus and, according to the infinity blur that you selected, will focus bracket from the minimum focus to the blur-defined infinity. Several bracket to bracket overlap strategies are covered, eg none, or at CoC/2, or at CoC/3 or at the diffraction corrected defocus CoC.

At each focus position the script can take various exposures, eg:
  • two additional time based exposures at +/- or +/++ or -/-- (at 1, 2 or 3Ev)
  • one additional ISO bracket at either ISO 800 or ISO 1600, set according to the when your camera's ISO invariance zone kicks in
  • one zero-noise time bracket at 4Ev
In the tabletop example below, I positioned the flower a couple of inches away from the camera and used the Mac2Inf option, together with the zero-noise exposure bracket option.

This resulted in 17 focus positions, with two exposures at each focus station, ie 34 images.

The images were processed in Lightroom as HDRs and then exported, via a round trip, to Helicon Focus. Base exposure, for the highlights, was ISO 125, F/5.6 at 1/60s. The zero-noise exposure was at 1/4s.

Here is the resultant test image, albeit only lightly 'touched up' in Helicon Focus, ie I should have spent a few more minutes touching up around the petals. Nevertheless, I hope this example gives readers a flavour of the script's power.

As usual I welcome any feedback.

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