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 p.22 #15 · Z8 extremely unreliable/inconsistent AF in mildly low light | |
ronno wrote:
In the above example, the Z8 had a hard time going from close to far focusing, in the below it's the opposite, the Z8 would not go from focusing far to close **this was well within the close-focusing limit of the lenses**…
And again, I was only doing these tests at home because the camera was failing to focusing when I was actually trying to shoot stuff out in the real world.
It's not random, what the camera does; it follows its own logic.
In the case of your video, the background is highly detailed while the "subject" doesn't have a lot of fine detail, it's fairly narrow, and it's not recognized as one of the subject types the camera has been programmed to handle (people, animals, birds, vehicles, and planes). If the subject is not recognizable as one of the subject categories (with subject detection on), the camera will focus on contrast, brightness, and presence of vertical lines. In the case of your scene, the background has overwhelmingly more detail, more area (part of the frame), brighter light, and neither has a recognizable subject that falls into one of the categories the camera was taught to detect.
If you replace the foreground object with a person, for example, and give some LED panel lighting on the subject so that the face is properly lit, I would venture to guess that the camera would handle the situation correctly nearly 100% of the time. At least this has been my experience, videographing scenes with people using the Z8.
Canon R5, for example, due to its dual pixel AF, has an order of magnitude greater number of phase-detection focus areas than the Z8 or Z9. This means that a subject that is narrow is always going to hit phase-detection sensors in the Canon while in the Nikons, there are gaps between phase-detection sensors. This is a matter of tradeoff, as the Nikons have advantages in other areas as a result of the different designs (such as heat management and long-exposure noise). I can see the appeal of having every pixel contribute equally to phase-detection and contrast-detection, this results in a system where the subject can be anywhere within the frame (except the peripheral areas aren't covered by phase-detection in either system) each part of the frame being treated equally and so there is a sense of smoothness and consistency as you turn the camera with the subject position shifting in the frame. If you need this, then the Canon has the advantage.
However, if you have a properly lit person in the frame in place of the object, you'd probably find the Nikon AF works just fine, as I have. I am not suggesting the AF system is perfect but simply that it works very well for the real-world situations that I've used in, with few exceptions (and those are in wildlife photography with very small subject against the light). Suggesting that it can only successfully focus 1/3 of the time in those transition is specific to your scene where there is no way for the camera to know what the intended subject is and it's not among the programmed cases, so it follows its own logic in the absence of subject detection, i.e., focus on something with a lot of brightly lit, high-contrast detail. In those 1/3 cases where it does focus on the foreground object (that it doesn't recognize as a subject and that doesn't have a lot of brightly lit, high-contrast, vertical detail), probably some phase-detect sensors happened to hit on some part of the foreground object which had detail. The appearance of inconsistency is created because the phase-detection sensors have gaps and only cover a fraction of the sensor area. A consistent result can be achieved using some of the following: 1) use a subject which the camera can recognize, 2) light the foreground subject properly rather than have it darker than the background, 3) use a narrow focus area mode that matches with the subject size and shape (preferably so that the area box is fully within the subject when finishing the camera pan), 4) use manual focus to adjust the focus from the background to the subject in a controlled way. (The focus ring speed is adjustable with the latest firmware of most lenses which makes it easier to achieve aesthetically pleasing focus pulls).
I can completely understand that you'd prefer something that does what you want without having to think about these things, and of course, if something else works for you you'd rather use it. That's perfectly fine. However, the recent post by CarlRichard which reactivated the discussion in this thread indicated that he wants to use the camera to photograph people ("portrait work which is mainly of children in outdoor available light context (not exactly dark night but golden hour/against the sun/sometimes sunsets)") and a republishing tests which do not include people as subjects can give a misleading impression of the performance of the camera in a context relevant to the person asking the question. Please, let's try to focus on solving real-world problems relevant to the people asking the questions.
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