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p.9 #20 · p.9 #20 · Steve Perry on the Z9 with FW 4.1 - follow up video | |
mogul wrote:
Just looking at S. Perry's video comparing the Sony's 200/600 to Nikon's 180/600.
Racking a lens from MFD to Infinity is not an accurate indication of AF speed during actual usage, and is not a normal situation you run into in the field. AF speed is not perfectly linear throughout the range, and not every lens has the same physical AF travel, which are other reasons why lens AF speed is so difficult to measure objectively. You might have a lens that is slower to move through it's full range but is faster from, say, 10m to 30m. You could also have a lens with a faster motor, but takes longer to move through the range because the physical distance it has to move lens elements is greater.
You would need to somehow track a subject that you could control the speed of coming towards or away from the camera and increase the subject speed until the lens can't keep up - that failure point would be the limit of either the camera body or the lens AF motor. It's just a really difficult thing to measure in a meaningful way due to the variables you have to control. I've always thought one of those robotic bunnies they use at horse races would make a good target for AF testing because it's fast and repeatable, but I have no idea how you'd gain access to one of those haha.
In the case of the 200-600 and 180-600, those are both the "value" zooms, and neither represents the fastest focusing lens Nikon/Sony have to offer. We know the 180-600 can keep up with 120FPS on a Z8/Z9 with full AF/AE between each frame, I would expect the Sony will be able too as well on the upcoming A9III.
You can track fast action with surprisingly slow focusing lenses, for example a fast bird like a swallow headed towards the camera is easily achievable even with older budget zooms. Motion perpendicular to the camera barely uses the AF motor so that is not an issue in any case. The speed at which pretty much any modern lens can adjust to subject distance changes once locked on is adequate for most subjects. There are AF speed differences in the middle of the AF range between lenses but they are incredibly difficult to measure objectively and usually not the weakest link. If you are someone who often finds themselves needing to go from literal MFD to infinity and back regularly, and would miss a lot of shots if you were a fraction of a second slower, then the way Steve measures would be applicable to your use case. To be fair, that is pretty much the only way anyone can measure in their back yard for YouTube or whatever, but it doesn't translate well to use in the field.
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