AF fine tune and focus shift for fast lenses

Started Sep 12, 2016 | Discussions thread
primeshooter
primeshooter Veteran Member • Posts: 6,067
Re: AF fine tune and focus shift for fast lenses

Marianne Oelund wrote:

Ryan Mack wrote:

My understanding is that Nikon's AF system cannot take advantage of lenses faster than 2.8.

That's the Canon AF system, but only for its better bodies. Their lower-level bodies, and all Nikon SLR's, will only use the f/5.6 circle for AF.

Why do people go on constantly about lenses' that are f/1.4 are able to focus easier as they let in more light? I had heard you post before explaining that it wasn't the case. Is this just misinformation?

Why 5.6! That seems ridiculous? Why doesn't the system in nikon slrs take advantage of at least 2.8, or wider?

Does that mean for a 1.4 lens that it is focusing based on where the lens focuses at 2.8?

The AF system uses a parallel optical path, which must be aligned to achieve the same perception of focus as the image sensor. The answer to your question depends on whether or not the AF system was aligned for the lens as it focuses at f/2.8. The user can of course modify this with fine-tune.

Specifically, it seems many 58 1.4 lenses need a significant positive fine tune adjustment at 1.4 and that lens is known to have a significant frontwards focus shift at 2.8. Is that causation or are they unconnected?

Lens focus shift isn't seen by the AF system.

Starting with models released in 2014, Nikon added a compensation feature to AF, which basically works by biasing the fine-tune value according to which aperture the lens will be taking the image at. This requires the camera to have tables of focus-shift values for various lenses. Cameras made prior to that time, have no such compensation and must be fine-tuned using compromised settings.

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Source credit: Prov 2:6
- Marianne

Correct me if I'm wrong, but I constantly see people going on about focusing fast manual lenses with nikon DSLRs. They say something like 'well I just MF using the viewfinder at f/1.4'. Some admit to using the range finder dot but many argue that the screen shows 1.4 dof which I am sure it doesn't? It's correct isn't it, that the focus screen shows the light and dof for about 2.8 and nothing less, so with a 1.4 lens, MF must be with the rangefinder dots, right?

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