Wednesday, October 2, 2019

Hand Held Bracketing Script - Version 2

A short post to introduce my Magic Lantern latest script: an updated Hand Held Bracketing Script.

The script has been written for a specific use case: namely when you can't use a tripod and you are in a high dynamic range environment, eg like a cathedral, and a single image, dual-ISO or not, isn't sufficient.

In addition, the use case is best exploited with a wide angle lens, ie focal length less than, say, 30mm.

The script is based on your base exposure being set for the highlights, eg following an ETTR. But you can set the base exposure anyway you wish. In addition the script makes use of the minimum shutter setting in the ML ETTR menu: so this must be set, eg at 1/30s, say.

The script 'exploits' the fact that Canon cameras exhibit ISO in-variance above a certain ISO, usually around 1600. Setting the ISO above this in the camera is usually pointless, ie all you are doing is reducing photon capture. Of course, your shooting needs may dictate higher ISOs, eg shutter speed: but that is your choice.

The script's menu allows you to control the script's functionality:

On or Off simply does what it says.

Delay allows you to add an additional delay before the script functions.

ISO logic allows you to select the bracketing ISO, eg "Float", "800", "1600" or "3200". If float is selected the ISO bracket will be taken at the ISO Ev lift, as set in the next menu item. Thus, if the base ISO is 100 and the Ev lift is set to 3, the ISO bracket will be taken at ISO 800.

If the ISO logic is set to an explicit value, eg 3200, the maximum ISO bracket will be taken at that value, irrespective of the base ISO value.

The script is triggered by doing a long half-shutter press of more than 3 seconds.

The script will take either two or three brackets. 

If the base shutter is equal to or slower than the ETTR min shutter setting, then the script will take two brackets:
  • Min Shutter at base ISO
  • Min Shutter at the higher ISO
If the base shutter is faster than the ETTR min shutter setting, the script will take three brackets:
  • Base Shutter at base ISO
  • Min Shutter at the base ISO
  • Min Shutter at the higher ISO
The script sets up ML's advanced bracketing, so you don't need to worry about any starting values. However, at the moment, the script doesn't reset the advanced bracketing back to the start condition. In fact the advanced bracketing is left on.

To illustrate the output from the script, I used my 5D3 with an IRIX 11mm at F/4. The test subject was inside my house, looking up at the ceiling lights. I ETTRed, with a min shutter of 1/30s, to generate a base shutter of 1/125s at an ISO 100. I set the explicit ISO to 3200.

The script took the following three exposures:


I ingested these into Lightroom and used LR's HDR Photo Merge to generate the following image:

As usual I welcome any feedback on the script, ie its usability or ideas to make it better.

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