m43 Focus Speeds on EOS Adapted Lenses

The significant jump to 1053 cross type AF points on the new OM-1 body led me to wonder if this might somehow also improve autofocus speed on adapted EOS lenses using a Metabones adaptor.

AF speeds on native m43 lenses is typically very fast.  It is significantly slower on 43rds lenses but can perform reliably especially on bodies that have phase detection (https://jimchungblog.com/2017/02/08/focus-speed-with-43rds-legacy-lenses/).  I have also used EOS lenses paired with a Metabones adaptor but limited to low focal length lenses of less than 100 mm.   As you enter the world of telephoto lenses, the lenses simply will not attain a confirmed focus lock unless the lens happens to already be close to the correct focus position.  

And that is a real loss  for people who shoot wildlife, sports, and aircraft.   The new Zuiko 150-400 f/4.5 sounds like the ideal instrument but is very expensive.  I have a trio of Sigma telephotos which are extremely affordable and offer a wonderful range of focal lengths:  the 150-300mm f/2.8, the 500mm f/4.5 prime, and the 300-800mm f/5.6 monster. 

Screen Shot 2022-05-17 at 10.22.28 PM
Target was an apartment building 400m distant. Lenses were set at maximum aperture, bodies to ISO 800 and 5 cross AF point pattern in the center. The first number indicates the minimum distance scale reading the lens had to be preset in order for AF to be confirmed. If the distance was set any further from infinity, the lens would hunt and then freeze without getting close to true focus.

So there was no significant difference in AF performance amongst the bodies.  The smaller the focal length, the closer to zero distance the lens could be preset and still achieve AF lock.   This explains how using very short focal length lenses works in the real world since the travel range of the focusing elements is so short that the initial surge of movement puts the object so close to focus that the iterative algorithm used is not confused and can continue to refine the movement steps until AF is confirmed.  

Still, these large telephotos can be useful for wildlife work since most wildlife is shot at near infinity and it isn’t hard to tweak the focus manually until the AF can take over.  What it likely can’t do is track objects correctly when they are moving towards and away from the camera because AF response is likely to be too sluggish to keep up. 

You might expect that newer, current Sigma lenses would do better but it’s also a hit and miss.  The Sigma 60-600mm does focus more reliably like a 43rds lens does (https://jimchungblog.com/2020/02/23/an-alternative-to-the-zuiko-150-400mm-f-4-5-telezoom/) but the Sigma 100-400 was just as stubborn as my older trio of Sigma lenses. 

One of the unintended discoveries is that the Metabones adaptor do not mount on the new OM-1 body due to a very slight change in the clearance of where the EVF (or where a pentaprism in a DSLR would be located) resides over the lens mount.  The EOS-m43 adaptor required some slight filing to clear the structure during rotation, the Speedboosters would require considerably more alteration to fit due to the thickness of the metal and proximity to its control dial and with the new sensor it is unknown if there is actual clearance internally for the optics of the Speedbooster.   Interestingly, I confirmed the Viltrox clone of the Speedbooster does fit and functions well with the OM-1.

1 Comment

  1. Thanks for all your work.
    I’m looking at the Sigma 60-600mm S for birding, using my E-M1 III. I’m also hoping the later edition date of 2018 will also equate with faster AF response times.


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