Manual focus problem with an XF56R on an XT3

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rlx
rlx Contributing Member • Posts: 969
Manual focus problem with an XF56R on an XT3

This is the first time I use an XF56R and as I was trying the manual focus I noticed some strange behavior.  I have been using manual focusing on a XE1 for many years and I have the XT3 for nearly one year now. It is not that I wish to use manual focus with the 56; however I needed manual focus for one specific test  so I came across that problem.

The problem is that while fine tuning the focus the lens suddenly jumps a bit and becomes slightly out of focus. I can hear the focus motor when this happens.

I checked for and discarded a few possibilities like 1) poor electric contact (I cleaned the contacts) and 2) the focus ring operating mode (linear or not) although the problem is more apparent in linear mode.

Manual focus typically is done with the lens wide open (f/1.2 here) so I tried with the iris stopped down to f/1.8 and the problem disappears.  I tried smaller apertures and still no problem.

So the manual focus issue occurs only at f/1.2 or nearby.

Did anyone else meet that problem (jumping out of focus suddenly while fine tuning the focus at f/1.2) ?

Maybe there is some limitation related to f/1.2 here. I am saying this since I had a 56APD for a weekend last December and I didn't meet that problem.  Recall that the 56APD is optically more like a f/1.7 lens rather than a f/1.2 lens since the APD acts as an iris to start with.

Fujifilm X-E1 Fujifilm X-T3
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