Issue with AF when using a EF to RF adapter

[Sudhir Shivaram]

Yes, using an EF-to-RF adapter on your Canon EOS R with the Sigma 60-600mm f/4.5-6.3 DG OS HSM Sports (EF mount) can sometimes introduce autofocus inconsistencies. The issue you’re describing—AF shifting slightly after focusing—can be due to a few key reasons:

Possible Causes of AF Issue

1. Adapter Compatibility Issues

• Canon’s official EF-EOS R adapter works well, but third-party adapters (Viltrox, Commlite, etc.) can cause minor AF issues.

• Even with Canon’s official adapter, some third-party lenses like Sigma & Tamron may behave differently from native Canon EF lenses.

2. Sigma Lens AF Algorithm Differences

• Sigma lenses (EF) were designed for DSLR phase-detect AF, while Canon EOS R mainly relies on Dual Pixel AF (DPAF).

• The translation between DSLR-style AF and mirrorless DPAF through an adapter can introduce slight focus drift at the end of AF.

• Sigma firmware may not be fully optimized for RF mount AF behavior.

3. Lens Firmware Update Needed

• Sigma frequently releases firmware updates for better Canon mirrorless compatibility.

• You may need to update your Sigma 60-600mm lens firmware via Sigma USB Dock.

4. Focus Breathing or Slight Backlash in Focus Mechanism

• Some long zoom lenses (especially super-zooms like 60-600mm) have minor focus breathing or internal backlash in focus motors.

• This can cause a tiny shift in focus when you release the button.

5. Low-Light or Low-Contrast Conditions

• AF inconsistency in low light or low-contrast scenes can be exaggerated when using an adapter.

[Harjit Singh]

👌🏻

[Arun Kumar Srinivasamurthy]

Thanks, for your reply and suggestions. I am using a Canon official Adapter. Will check for the firmware update and purchase the Dock as suggested. Also I have learnt quiet a few things from your course regarding the setting to use with low light. will practice that.

Thanks for your advise.