This post is meant to finally clarify the MFA (micro focus adjust) procedure for using EMF AF Confirm chip.
I am a digital engineer by training originally. I know it said to enter using scale of 0-31. BUT it was never explained the relationship within the MFA scale for the adapter to actual MFA numbers we are use to (-20 to +20 in Canon). Most people leave their Camera MFA on 0, others seem to emulate the right value or use it as micro-adjustment to the value entered into the Chip.
For EMF chip MFA entry, instructions want you to enter 0-31 converts to 5 digital bits.
We need to understand the proper interpretation and effects of this 0-31 range on focus. This now has been confirmed via experimentation. (by Matt and others).
5 digital bits can be 0-31 in base-10, or if we need positive and negative values for MFA, it can
be -16 to +15 for the same 5 bits. This is the key part.
So here you go!! -->
Matt,
Thank you for sharing!
Your results seem to actually confirm my theory that the 0-31 scale more represents -16 to +15 MFA values (meaning more negative pulls focus forward in the result, more positive pushes focus back in the result) using 2’s complement digital representation to get negative & positive MFA from 0-31 entry values. Based on your results, using 2M resulting distance as the assumed correct / sharp live-focus.
Essentially, as you can see in the table below, the following would be the proper way to understand the entry of the 0-31 chip values that corresponds to MFA-like camera values -16 to +15 using the 2's compliment 5 bit representation within the 0-31 values.
Your distance results confirm this.
- As you went from entering 14 to 15, you pushed focus back.
- When you entered 16, you got maximum front focus
- As you increased from 16 to 29 you slowly reduced (less negative) the front focus settling on 27 (-5) equivalent for proper Phase detect focus.
