This discussion is interesting. I am a technical person and I debug things. Fact that with 100-400 the results are much different than with 200-600 is interesting to me.
I have some ideas.
This might be some compatibility problem that no change in settings will help to mitigate unless it is fixed in software or even hardware of camera. It might be hardware problem where different copies of lens would differ in results. This can still happen despite accuracy for still subjects. For still subjects the hybrid AF uses phase detect first and near end it corrects it using contrast detection or just though feedback loop which requires fast small changes to focus (where motors in lenses might differ). Also for a moving subject there may be no time to increase accuracy in the last step.
But perhaps some settings can help mitigate it. How to discover it?
The problem with birding is that you never get same scene so it is very hard to evaluate effect of change of settings. Best bet is to have artificial target. E.g. improvise engine powered merry go round with af target stuck on it. Still, a lighting might change and results with it, but variance will be lower than with birds. Perhaps best settings for that af target will be very different to best settings for photographing actual birds. But it is worth trying. If not, just use bird feeder and take pictures in same spot to decrease variance.
Next issue is cameras have so many features that interact between them. My guess of what settings could help:
Shutter:
- EFCS shortens delay between last AF measurement and picture taking. It makes bokeh worse at high shutter speeds, but probably it should be helpful.
- Use of electronic shutter may increase or decrease delay between last AF measurement and picture taking. Try it. To reduce rolling effects, avoid uncompressed raws which have slower scan time due to 14 bit processing (1/10s) than with 12 bit processing of compressed raws (1/20s).
- Try lower drive frame rate to let camera do more AF measurements between shots.
Stabilization:
- Stabilization when active takes CPU time (because it is not only in lens, but sensor is stabilized as well). It may delay picture taking from last AF measurement. It also takes more battery power which means CPU power management may reduce its frequency (this is also a place where different lenses with different motors and actuated mass could have different AF results). Turn it off. You need fast shutter speed for birds anyway. Stabilization may even have negative effect at high shutter speed.
Display/EVF features:
- There are options like higher quality EVF. Mostly likely higher quality settings will take some CPU time or reduce sensor AF time. Try turning them off. Higher viewfinder FPS might be better or not. Try both. Also using display instead of EVF might produce different results, it has different resolution, it has different CIPA battery rating. It might be still usable as EVF with loupe attachment.
- Camera can display a lot of things in overlay over the picture. Any actively changing displays, e.g. histogram, tilt indication can take CPU time that could be used for AF. Turn off zebras. Turn off exposure guide (it makes my A7iii slower to respond to dials). Turn off auto-review.
- Try changing NTSC/PAL Selector, it affects refresh rate when HDMI is connect and possibly even without it.
- There is an option to see image with simulated exposure or with different exposure that camera thinks is good for viewfinder (Cam2 / Live view display / Setting Effect). On my A7iii this impacts AF when viewfinder shows too dark or overexposed subject (though actual exposure in M mode is different, perhaps because of flash). Option that will expose well for AF sensing will likely be better. Try both.
Turn off auto features:
- It is well known that AF-A modes do poor job because of spending time to decide between AF-S and AF-C. It may be similar for other auto features. Including auto exposure (including Auto ISO in M mode), auto WB.
- Turn off IR control and other remote features (use airplane mode) that are active during focusing.
- Turn off DRO. DRO silently shortens exposure and changes tone curve to compensate.
AF features:
- Play with AF-C priority options (you already did that, right?).
- Use smaller areas where AF is active. Zone or L point instead of wide. There is a chance that camera will spend shorter time reading less AF rows (maybe not if information from whole sensor is used for tracking).
- Try different AF Tracking Sensitivity.
- If lens supports it (no idea) try different Aperture Drive in AF settings. Do not assume that focus priority is best like manual tells (it may be more complex).
FYI: I am a A7iii owner and I am just researching whether to get A7riv as general camera replacement for A7iii. I do not shoot BIF. A7iii has best AF of all the cameras I had (previously Nikon DSLR) though it is not perfect in small DoF conditions with some lenses so wonder if it gets worse or better with A7riv.
Aug 02, 2020 at 04:38 AM
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