Author Topic: [NO] Possible? work-around pseudo-MFA on Rebels?  (Read 2542 times)


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[NO] Possible? work-around pseudo-MFA on Rebels?
« on: February 20, 2014, 06:52:10 PM »
I was wondering if it would be feasible to implement a work-around MFA (micro focus adjustment) for Rebels and XXd series cameras like the 60d that don't have MFA.

  • Many lenses communicate with the body to report distance to subject. I've noticed a rather coarse value in the EXIF and LCD.
  • How much resolution is there in the chip register for this value? Coarse (cm?) or fine (mm?) or very fine (less than mm?)
  • If the chip register value was very fine, perhaps the distance from 10x magnified LiveView (MLV) could be compared to the value reported by the AF point?
  • Example: Carefully focused MLV reports 2500.00 mm for 50mm lens, and AF also reports a value very close to 2500.00 mm. This would indicate the AF was accurate, and MFA=0 for this combination of body + lens.
  • However, suppose there was some threshold of difference that indicated front-focus or back focus?
  • ML might be able to calculate the equivalent "fudge factor" MFA, and tweak the AF accordingly.
  • Or not?


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Re: Possible? work-around pseudo-MFA on Rebels?
« Reply #1 on: February 20, 2014, 08:25:34 PM »
I don't know if some higher quality lenses are better at this, but all the (non-L) lenses I've got only report "coarse" values or even worse. 1cm steps are the best, but even those could be off by a bit. 70cm could mean anything between 65cm and 80cm... focus adjustments maybe, micro not so much. The data is just not precise enough :(