EOS R - Lens Microfocus?

[mikul]

Is lens microfocus available on the EOS R? It doesn't show by default in the menu. It seems odd to have this missing from a new camera, especially one this customizable.

[RobertTheFat]

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@mikul wrote:

Is lens microfocus available on the EOS R? It doesn't show by default in the menu. It seems odd to have this missing from a new camera, especially one this customizable.

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I don't think you need it, because the autofocus mechanism is looking directly at what the sensor sees. The reason for it in a DSLR is to correct for discrepancies between the autofocus viewfinder and the sensor.

[mikul]

That's interesting, but it makes sense since the SLR had to focus from the mirror. I was seeing some softness in a previously sharp lens, but doing an A/B comparison with another camera showed me that I'm hallucinating.

[ebiggs1]

With a DSLR most of the light coming through the lens is reflected up by the mirror, into the pentaprism and through the viewfinder. A small part is deflected downwards to a dedicated autofocus sensor. This is called phase detection autofocus. It's advantage is it is fast. Disadvantage, it is sometimes less accurate.

Mirrorless cameras don't have what?  A mirror, therefore you can't direct light to a dedicated autofocus sensor. Instead they take a reading from the actual sensor. This is called contrast detect autofocus. Contrast detect is slower. A lot more stuff has to happen for it to find the sharpest AF point. It can be more accurate as long as teh subject doesn't move. At any rate this makes autofocus micro-adjustment unnecessary.

[RobertTheFat]

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@ebiggs1 wrote:

With a DSLR most of the light coming through the lens is reflected up by the mirror, into the pentaprism and through the viewfinder. A small part is deflected downwards to a dedicated autofocus sensor. This is called phase detection autofocus. It's advantage is it is fast. Disadvantage, it is sometimes less accurate.

Mirrorless cameras don't have what?  A mirror, therefore you can't direct light to a dedicated autofocus sensor. Instead they take a reading from the actual sensor. This is called contrast detect autofocus. Contrast detect is slower. A lot more stuff has to happen for it to find the sharpest AF point. It can be more accurate as long as teh subject doesn't move. At any rate this makes autofocus micro-adjustment unnecessary.

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To dumb it down to terms that even I can grok: Phase-detect autofocus works with photons before they've been converted to pixels by the sensor, and an SLR relies on a semi-transparent mirror to divert and collect them. Lacking a means of diverting photons before they reach the sensor, a mirrorless camera has to settle for an autofocus mechanism that doesn't require direct access to them.

[mikul]

Thank you for the excellent information on phase detect vs contrast detect autofocus. I'm surprised to hear the contrast detect is slower considering how quickly the EOS-R autofocuses. The reason that I was asking is that my go-to lens (16-35 2.8 II) has been giving me soft photos since I got the EOS-R, so I assumed that it needed to be adjusted (which I now know to be nonsense). I've since done A/B tests on my old camera and new and the lens is giving me similar results. Either this lens is much softer than I remember or it is having an issue and need to be returned to Canon for service.

[kvbarkley]

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@ebiggs1 wrote:

Mirrorless cameras don't have what?  A mirror, therefore you can't direct light to a dedicated autofocus sensor. Instead they take a reading from the actual sensor. This is called contrast detect autofocus. Contrast detect is slower. A lot more stuff has to happen for it to find the sharpest AF point. It can be more accurate as long as teh subject doesn't move. At any rate this makes autofocus micro-adjustment unnecessary.

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THe EOS R does not use contrast detect. It has phase detecting built right into the sensor.

[ebiggs1]

" It has phase detecting built right into the sensor."

The point is it is taken right off the sensor.