Re: Contrast Detect AF in AF-S mode with Z lenses and adapted lenses
snapsy wrote: gdsf2 wrote: snapsy wrote:
Agree that AF-S behavior on the Z might be different across different F-mount lenses, but I would have to see evidence of that rather than assume it to be true. As it stands I haven't seen any evidence of a CDAF confirmation cycle on any F-Mount lens I have used myself, nor have I seen a test by anyone else which proves it, while I have seen counter-evidence against it (Pinpiont vs AF-S precision).
I also agree it would be preferable to give users the option to enable a CDAF confirmation cycle for AF-S. However in the absence of such an option, considering how precise the Z's AF-S behavior is without a CDAF confirmation cycle then I agree with Nikon's decision to not have one. Not only would the CDAF cycle slow down AF acquisition but it also produces a jarring focus warble when looking through the viewfinder during AF, something I always found annoying on Sony's MILCs. IMO that warble greatly interferes with photographic experience of using Sony's cameras (which I still own btw).
As to whether or not future lens designs should be specifically optimized for CDAF, I agree it would be better than not optimizing for it but I don't really see a compelling case for it. As it stands Nikon isn't using CDAF in the normal course of AF on the Z, and for the few scenarios or users who might prefer CDAF the current non-optimized designs on F-mount lenses are perfectly adequate to the task.
I am confused. You state there is no proof that Nikon is using CDAF, and then go on to state they are not using CDAF. Where is the proof they are not using it? Why start with the assumption they are not using it?
The proof is twofold:
1) You can actually see when a camera is using a CDAF confirmation , especially on a slow-focusing lens. If you've ever used a Sony MILC this manifests as a focus warble during acquisition
2) Pinpoint AF, which is clearing using CDAF by the behavior exhibited by the lens, is more precise than AF-S based on MTF measurements performed by Jim Kasson. If AF-S were using a CDAF confirmation cycle the precision would be the same.
First of all CDAF may not be used for focus acquisition and still be used. In fact, if CDAF is used for focus tuning it won't be used for focus acquisition.
Second, you have made an inappropriate inference that if CDAF were used for fine tuning that precision would be exactly the same and if CDAF were used solely for AF. That would determine how the algorithm were written. It is certainly possible if not probably that using CDAF for the sole AF and using CDAF for fine tuning would have code using the CDAF in different ways. For example in CDAF only AF where accuracy and precision are paramount the CDAF cycle might check final processing 3, 4, or 5 times. Whereas when CDAF is used for fine tuning the CDAF cycle might only check final focus once. If that were the case you would expect exactly the results that Jim obtained. So, your inference that because these result are different AF-S must not be using CDAF fine tuning is based on the assumption that both modes of focussing are using CDAF in the same way. I think that assumption is invalid and therefore you inference is invalid.
Third, I am skeptical that you can tell that CDAF is used to fine tune by watching the lens. It is good to know how you have arrived at your conclusions. I think it is very flimsy reasoning and I am totally unconvinced.
Aug 17, 2019 at 01:28 PM
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