Firmware idea: Auto hyperfocal focus in Live View?

Started Jul 17, 2012 | Discussions thread
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Firmware idea: Auto hyperfocal focus in Live View?
Jul 17, 2012

Here's a simple idea that would be very helpful to landscape shooters. Rather than LV's CDAF always selecting the infinity position on the lens when focusing on an infinity object, how about a selectable option where CDAF instead finds the hyperfocal position?

The algorithm would be simple, something like:

  • Just prior to focus acquisition, stop the lens down if necessary to the dialed-in aperture (Nikon already does this on some bodies like the D800, Canon does not)

  • Initiate the CDAF scan (ie, searching for maximum contrast by sampling the sensor and varying the focus position of the lens), starting the scan from infinity and then moving toward MFD. Some allowance must be made for infinity tolerance/slop, so the logic needs to detect the "ramp-up" of contrast that would occur from an OOF infinity hard-stop towards the true "soft" infinity position of the lens.

  • Establish the hyperfocal focusing position of the lens by detecting the first decrease in contrast as the scan moves away from infinity. The proper delta threshold for this detection would need to be pre-established.

Alternately the scan can start from the MFD position of the lens toward infinity, and if so, detecting the plateau of the contrast increase that would occur once hyperfocal is reached (ie, when hyperfocal is reached the scan will have found the maximum point of contrast, and moving further toward infinity will not increase that contrast, so once the plateau is detected the scan can back up to the focus position of where the curve plateaued, which will be the hyperfocal position).

It seems to me firmware already has all this logic in place to support existing CDAF operation. I suspect the current implementations work on a contrast curve that, after fumbling onto the maximum point of contrast, move past that point to detect the contrast dropoff that puts them past the soft infinity position of the lens (toward the OOF "slop" at hard-stop infinity stop), to detect they've previously reached the maximum point of contrast, and then they reposition back to that maximum point of contrast, which will land them on the soft infinity focus position.

Nikon D800
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