AF tunning what actually happens?????

Started 8 months ago | Discussions thread
Horshack
Veteran MemberPosts: 4,151
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Re: AF tunning what actually happens?????
In reply to Roy Kikuta, 8 months ago

Roy Kikuta wrote:

Do you have more details - for example, how does the AF module/CPU communicate with the "silent wave" (ultrasonic?) focusing system in an AF-S lens? Since AF-S lenses contain CPU's, I assume the AF module in the body communicates digitally with the CPU in the lens - has anybody hacked the lens CPU or signal to actually understand what's going on? Is the fine tune "correction" applied during the phase detection/calculation, or is it applied in the signal sent to the lens - stated another way, is the fine tune "correction" applied in the body's AF module - or is it actually executed by the lens CPU? I've heard that only one lens drive command is applied - with no secondary phase check(s)/lens drive command(s) applied - in order to speed up AF operations - is this true? I'm not criticizing your explanation - I'm simply looking for more details because it's a subject that's dear to my heart

Evidence strongly suggests that fine tuning affects only the phase detection part of the process and does not alter the commands sent to the lens. The first piece of evidence is WilbaW's excellent articledescribing how PDAF is a partially closed-looped system that relies on multiple phase sensing:lens movement sequences...in such a system you can't reliably alter the outcome by biasing an input. The second piece of evidence is that a body+lens can be accurately tuned without ever engaging the AF motor (DotTune), with some background information here.

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