backAutofocusContrast detect autofocus works by maximizing differences among adjacent pixels.Phase detect autofocus works similarly to split prism, comparing image slice pairs from different angles, and calculating how much refocus is wanted to bring slice features in phase. In theory, perfect phase detect autofocus can correct focus in one step. Practically, mirrorless in-sensor phase detection is less precise, wanting contrast detect autofocus for final correction. While mirrorless AF is imprecise, direction for correction is known, minimizing hunting. The camera must estimate how far the image-side focal plane is going to move for a given command to the lens. If it has that information -- and there are several possible ways of making that happen, but I don't know which are actually used -- then PDAF can work. Sony patent Mirrorless vs. DSLR - PDAF Tony's PDAF video α7RII PDAF cannot be turned off for native lenses, only its display. Autofocus optimizes red channel, not green. SONY updated α7II and α7RII firmware after release to allow fast PDAF on adopted lenses. Brian Smith's a7RII Canon EF Smart Adapter Tests (2017) Metabones, Fotodiox, Viltrox Update includes Sigma MC-11 Back Button AF on Sony a7 Activating Back-Button Focus: 1. Menu > Custom Settings > Pre-AF > Off 2. Menu > Custom Settings > Custom Key Settings > AEL Button > AF On. 3. Menu > Custom Settings > Custom Key Settings > AF/MF Button > AF/MF Ctrl Toggle. 4. Menu > Custom Settings > AF w/shutter > Off. α7R II Focus Performance and Metering Mechanisms for focus peaking differ from CDAF Sony α7 PDAF sensors are in what would be the blue channel. Sony α7RIII tweaks focus by contrast detection (CDAF) after initial phase detection autofocusing (PDAF). Conventional wisdom has that CDAF tweak at the taking aperture so that focus shift in Sony lenses is not a problem. The α7RIII does not support manual AF Adjustments for native lenses. Conventional wisdom has that unnecessary, because CDAF tweaking. In fact, α7RIII corrects for focus shift only in AF-S, not AF-C. Shot-to-shot focus variation is worse in continuous than single focus mode. |
| maintained by blekenbleu |