Wednesday, June 16, 2021

CHDK Landscape Bracking Script: Latest release

In the EOS Magic Lantern environment one can have multiple Lua scripts running. Thus I will typically have DOFIS running to give me DoF and focus stacking feedback in LV, and then run MUSIC to allow me to capture complex bracket sets.

In the CHDK environment  you can only have one script running at a time.

Thus my Landscape Bracketing Script (LBS for M3 and non-M3 CHDK cameras) tries to provide both DOFIS and MUSIC functionality in Canon Powershot cameras.

The latest release of the non-M3 version of LBS, download from the right, has a new feature that some may find of value.

As with all LBS use cases, LBS shows its worth when you need to capture a complex bracket set, eg for focus blending, and/or exposure blending.

LBS was written to exploit the 'fact' that the foreground will usually be captured at one exposure setting, whereas the sky will usually require a different exposure to the foreground and not require focus bracketing.

Plus the foreground may require multiple focus and exposure captures, eg for dynamic range or wind, whereas the sky will only need a single ETTR capture at 'infinity'.

The new LBS feature allows you to capture a simulated ND bracket set, at infinity. This bracket set, covering up to ND5, may be of value if you wish to, say, have tack sharp foliage and rocks, that may require focus and exposure or wind bracketing, with silky smooth flowing water. 

Trying to achieve the above in windy conditions, with an ND filter attached, will be a challenge, ie long exposure times at each focus station. Having a simulated ND bracket set may not be perfect, but it will likely be better than having nothing.

As an example consider the following test scenario, where your scene has a stream in the foreground, with water flowing over rocks, and there are flowers close to you in the foreground.

Using the LBS menu you set up the following options:

  • H/x2INF: to capture from a fraction (x) of the hyperfocal (H) to the defocus blur defined infinity;
  • x set to 5: thus taking focus brackets, less than H, at H/5 and H/3, and giving a near DoF at H/6;
  • Overlap blur set to the CoC: that is for the DoF brackets
  • Exposure bracketing set to Wind: thus taking an additional exposure at each focus station at 3Ev difference compared to the base exposure, ie 3Ev difference in ISO and shutter speed, giving a similar 'exposure' to the base shot;
  • Infinity blur set to 3H: that is an infinity blur shot three times the hyperfocal, giving an infinity blur of about CoC/3 microns;
  • Infinity bracket option set to ND;
  • ND set to 4: that is 16 images captured at infinity and at the foreground exposure setting, to be statistically blended in Photoshop, say;
  • Sky bracketing on: which will capture an auto ETTR image for the sky at infinity
  • Bookends set to on

Based on the above prescription the script will capture the following bracket set for post processing in Photoshop:


[H/5 @ s seconds] +  [H/5 @ 3Ev from s & 3Ev ISO up]

[H/3 @ s seconds] +  [H/3 @ 3Ev from s & 3Ev ISO up]

[H @ s seconds] +  [H @ 3Ev from s & 3Ev ISO up]

[3H @ s seconds] +  [3H @ 3Ev from s & 3Ev ISO up]


 [3H x 16 images @ s]


    [3H @ ETTR for the sky]  


That is, 14 images triggered by a single half shutter press.

In future posts I'll talk about how to post process such complex bracket sets. For now, additional info on the script may be found here.

As usual I welcome any comments on this post or any of my posts.

No comments:

Post a Comment