Monday, May 17, 2021

M3 Bracketing: The latest

As I haven't posted for a few days, I thought I would provide a short update on the latest developments of my M3 Bracketing script.

Thanks to the gurus over at CHDK, especially philmoz and reylap, the CHDK UI is now rock solid, with no (repetitive) flickering.

The only (known) thing that remains broken is the liveview CHDK histogram; but as the M3 has a Canon liveview histogram, this is not a great loss. Hopefully the CHDK histogram display will be fixed soon, but until then the script switches off the CHDK histogram. 

The bracketing options have been reconfigured and are now very versatile, and optimised for land/city-scape photography.

There are three bracketing options:

"Focus bracket?" {Off X2INF Min2INF Manual}
"Exposure bracket?" {Off 1(4Ev) 1(3Ev) 1(2Ev) 2(2Ev) 3(2Ev) ISO Auto 
Wind3Ev Wind4Ev}
"Sky Bracket?" {Off 2Ev 3Ev 4Ev 5Ev 6Ev ETTR}

Focus bracketing has three active options: two auto options and one manual option. 

The auto options will take focus brackets from either the current point of focus to infinity (X2INF) or from the camera's focus minimum to infinity (Min2INF). The focus brackets will be selected according to the overlap (CoC) criterion chosen, ie between 5 and 30 microns. A sensible number being 20 microns. The script provides feedback as to how many estimated brackets will be taken up to the hyperfocal. Once the images up to the hyperfocal have are taken, the script will then take a further focus bracket at the selected infinity point, ie between 2 to 4 times the hyperfocal, giving an infinity defocus blur of the CoC divided by the number selected. Three is a sensible number to use.

When auto focus bracketing (X2INF or Min2INF), you can select single image capture (exposure bracketing = off) or select one of the various exposure options: see below.

The manual focus option allows you to take a single image or selected exposure brackets, with a sky bracket (see below) if requested.

The selected exposure options are (note, because the script is optimised for landscape use, the base exposure is assumed to be at ISO100):

  • Off = just take a single base image
  • 1(4Ev) = take the base (ETTR) image and an additional (longer) one at -4Ev, ie for the shadows
  • 1(3Ev) = take the base (ETTR) image and an additional (longer) one at -3Ev, ie for the shadows
  • 1(2Ev) = take the base (ETTR) image and an additional (longer) one at -2Ev, ie for the shadows
  • 2(2Ev) = take the base (ETTR) image and two additional (longer) ones at -2Ev and -4Ev
  • 3(2Ev) = take the base (ETTR) image and three additional (longer) ones at -2Ev, -4Ev and -6Ev
  • ISO = take the base image an an additional image at an ISO of the selected value. The value should be the start of the ISO invariance zone of the M3, eg say, ISO 800ish
  • Auto = take as many brackets at required, at a delta of 2Ev, until the last image taken is an ETTR. Thus, in auto mode, set the base exposure for the shadows
  • Wind3Ev/Wind4Ev = take the base image and the selected wind bracket at either 3Ev or 4Ev difference, such that the exposures are the same as the base image, ie a faster shutter at higher ISO to freeze motion, say, in flowers

Finally sky bracketing options are available when auto or manual focus bracketing. In auto focus bracketing mode, the selected exposure brackets will be taken at each focus bracket station until the infinity focus criterion is reached. At this point, if selected, a sky bracket will then be taken. The options being:

  • Off = no sky bracketing
  • 2Ev to 6Ev = take an additional image at the selected faster shutter speed, eg to capture sky highlights
  • ETTR = take an additional image at the sky's ETTR point (this is the best option to use as it is scene aware, ie fully automatic)

In manual focus bracketing mode, the sky bracket will be added to any exposure brackets. Manual focus bracketing has the additional option of using traffic lights to tell you when you have refocused to the perfect focus point for the next focus bracket.

In addition the script has an auto ETTR option that is selected in ALT mode by pressing the right key. If pressed, the camera will adjust exposure until the ETTR value is reached.

The above options are fully compatible with each other; giving you full control over getting the perfect exposure and focus image bracket sets for blending or tone-mapping in your favorite post processing software.

When the script is running it will display the info bar at the top of the screen. This bar will show in ALT and non-ALT modes: plus, unfortunately in other camera modes as well.

The script needs the ALT key to not be the full shutter or the M-Fn key, ie use the VIDEO key.

In both ALT and non-ALT modes, the shutter is available for single image capture. In ALT mode the M-Fn button, next to the shutter button, acts as an addition shutter button. In manual focus mode the selected exposures and sky bracket will be taken, with a delay if requested in the script's menu, when the M-Fn button is pressed. In auto focus mode, the selected focus and exposure brackets will be taken, then, at infinity, the selected sky bracket will be taken.

The latest version of M3 Bracketing can be downloaded from the link on the right.

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

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