Sunday, April 30, 2023

QDFS: A few handheld enhancements

In this post I'll discuss the latest version of my Canon M3 Quasi Depth of Field Script. 

In addition to some UI changes, eg focus distance is now stated in cm, I've added some bracketing enhancements. The latest version may be downloaded from the link on the right.

The new menu options look like this:

#coc = 15 "CoC (um)" [5 30]
#brak = 0 "X bracket mode?" {ISO Tv HandH Auto->H}
#b_val = 0 "X Bracketing Value" {Canon 1Ev 2Ev 3Ev 4Ev 5Ev}
#sleep_time = 0 "Delay (s)" [0 10]
#dis = 1 "Display" {#Bracks Focus}
#lensmag = 0 "Get Mag" {Off On Dynamic}
#reg = 1 "H/x Reg Dis" [1 3]
#offset = 1 "Console offset" [1 12]
#title = 1 "Title Line" {Off Full Exit}
#ettr_zero = 3 "ETTR zero count" [0 20]
#hhmin = 30 "HH Min Tv (1/x s)" [10 100]

Here we see the two new exposure bracketing options. One for when hand holding (HandH) and one for auto bracketing (handholding or not), from an exposure set for the shadows, with the script auto bracketing until the ETTR exposure is reached. The bracketing steps may be set at 1, 2, 3, 4 or 5 Ev (b_val).

The ETTR 'zero' count may be set from 0 to 20, ie how many counts are allowed in the top 1/10 Ev of the histogram. In addition, when using the HandH option, you can set the slowest acceptable handheld shutter value, with the script adjusting if the 1/focal_length criteron is not met.

The handheld (HandH) option, which works well in high dynamic range environments like churches, is best used in the following way:

  • Set the Ev value to 4 or 5 Ev
  • Set the ISO to 100 (note you can use a higher ISO if necessary)
  • Set focus
  • Use the script (RIGHT button) to set an ETTR exposure. The script will check it meets the handheld criterion
  • Trigger the bracket set and the script will take the following three brackets
    • Image 1 at the ETTR ISO 100 setting
    • Image 2 at the handheld shutter value at ISO 100
    • Image 3 at the handheld shutter value and at an ISO of the set Ev value, eg 4Ev = 1600

The Auto->H (where H = hightlights) can also be used for handheld bracketing, ie where shadow noise is likely to be an issue in a single image capture. Of course, the Auto->H option can be used to take non-handheld bracket sets as well, ie at any ISO.

  • Set the Ev value between brackets, eg 2Ev
  • Set focus
  • Set the shutter to the handheld value for the focal length you are using, eg on a WA lens 1/30s, or slower if you haven't been drinking a lot of coffee
  • Adjust the ISO, up to, say, 3200, until the histogram (Canon or CHDK) indicates a suitable ETTL state. Adjust aperture and refocus as required
  • Trigger the bracket set and the script will take the following brackets
    • Image 1 at the manually set ETTL and ISO setting
    • Image 2 to n, at the ISO setting and by adjusting the Tv value until the ETTR condition is met

As an example of using the auto option, here is a handheld test image I just took from inside my dark garage, looking out. The focal length was 11mm and the base shutter was set to 1/30s. The ISO was set to 3200.

The script then took the following additional ISO 3200 images until the ETTR criterion was met: 1/125s and 1/500s.

The resultant test image, after processing with PureRaw 2 and Lightroom, looks like this:

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


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