Friday, August 5, 2022

Quasi Depth of Field Scale in Action

UPDATE:  although the QDFS script works, unfortunately I recommend you not use it for now. The reason is related to how some of the calls interact with the Canon side. The problem has been recognised by the CHDK developers and I’m hopeful a fix will be implemented soon.

In the last post I introduced the Quasi Depth of Field Scale (QDFS) script (latest version on the right) that I wrote to aid manual focus bracketing. The script has been written mainly to cover focus bracketing for wide angle lenses, and has been tested on the EF-M 11-22mm.

The reason for the WA warning is that, once you go move away from the WA zone, the number of focus brackets you need to take gets large for deep focus scenes. In such cases it is better to use an automatic approach, for example my Landscape Bracketing Script.

In this post I’m demonstrating QDFS’s functionality in three short videos.

This first video shows QDFS starting up and how the in-bar information is handled:


If you are focused short of the hyperfocal, then QDFS shows (on the right) an estimate of the number of focus brackets to get from your current focus position to the hyperfocal; where you can add in an infinity bracket.

If you are focused beyond the hyperfocal and short of infinity, QDFS shows (on the left) an estimate of the infinity blur in microns.

If you are focused at infinity, QDFS shows four pieces of information: the circle of confusion in microns; the minimum focus distance (MFD) in mm (from the front principal);  the hyperfocal distance in mm (from the front principal); and the total number of brackets required from the MFD to the hyperfocal.

BTW because QDFS shows the Canon reported distances in the console area, if switched on, we now have an estimate of where the front principal is located, relative to the sensor. Namely, at the MFD reported by Canon, minus the MFD reported by QDFS. In the video above, the MFD, relative to the front principal is reported as 93mm. In the above, knowing the Canon reported MFD, relative to the sensor, is 150mm, means an estimate of the front principal, relative to the sensor, is 150-93 = 57mm. A better estimate than using the thin lens position; in this case, at F(1+m), ie 11(1+0.3) = 14.3mm.

In this next video we see how QDFS handles changes in focal length and aperture. Focal length changes result in a recalibration, whereas changes in aperture are handled dynamically in real-time:


Finally, in the last video we see focus bracketing taking place in QDFS:

Finally, pressing the INFO button will toggle the depth of field scale on and off, ie to support composing.

Bottom line: if you are lucky enough to have a Canon M3 (M10 or M100) that is running CHDK, you may wish to give my QDFS script a try out.

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

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