Personal View site logo
Cinema gear deals, direct from factories - Gear deals and Gear deals section. Also check Cameras, lenses, software, gear deals.
You support is vital for us. To keep this place ad free and independent, select one of the options below.
Donations are going to community support costs, hosting, etc. Your support allows to improve and expand this site.
Improve DFD contrast based auto focus for video.
  • Dear Panasonic,

    I love to see a better video auto focus system. DFD has already removed the first wrong direction start of the focus pull, but I like to address the second wrong direction autofocus pull, the "focus confirmation" rack at the end of the auto focus pull.

    I'm not an engineer but I like to understand what is happening what, how, where, when and why.

    At this moment the Auto Focus system for video looks the same as for stills. And for stills it works fast and well, accept in continuous high when it has a hard time keeping up with fast action. For video (akin to a very high number of stills) the AF is way to slow, and the focus confirmation pull is very distracting and jarring.

    If DFD is able to measure the blur amount, and therefore can measure how far the subject is, the I think a reprogramming of the focus system can help to get rid of that jarring focus confirmation refocus.

    I can think of this focusing system:

    Focus pull situation:

    1) DFD measures the amount of blurr, 2) compares it to the current focus distance, 3) estimates subject distance, 4) smoothly starts racking focus, 5) measures amount of blur half way racking focus, 6) checks the blur shift amount of the first and second measurement, outputs second focus target distance, 7) at the last part of the focus rack the focus speed eases off to arrive at the second estimated focus distance.

    Continuous AF situations:

    1) DFD measures the amount of blurr, 2) compares it to the current focus distance, 3) estimates subject distance, 4) smoothly starts racking focus, 5) measures amount of blur half way racking focus, 6) checks the blur shift amount and compares it to the first measurement, calculates subject movement, 7) rack focus to second focus target distance, 8) checks the blur shift amount and compares it to the previous measurement, calculates subject movement, 9) repeat 7 and 8 until no blur.

    10) If subject leaves the frame maintain the current focus distance for x time before starting with 1 on the new subject in the assigned focus area.

    Maybe DFD blur measurements are hard & slow, so having measurements while the camera is auto racking focus is harder to do, but I prefer a slower focus much over racking past the focus and racking back in video.

    As a compromise DFD could be used to make a 1 time focus distance estimate, the focus racks smoothly (s curve) to the estimated distance, and stops (without racking past the estimate focus distance AND racking back). This would be good enough for a G85, and the more processing heavy higher DFD sample rate for the high end GH5. I must admit this all hinges on DFD accuracy in measuring the blur and estimating the subject distance.

    What do you people think? Love to learn how the current contrast and DFD actually works. Love to hear your suggestions of how to improve AF.