Fred Miranda Offline Admin Upload & Sell: On
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josh-himes wrote:
Thanks for this info Fred. I have had the 50 F1 for a week and it's an excellent lens. I noticed that my copy front focuses by a small but noticeable amount wide open with the M11 rangefinder. I tested for focus shift at 1M with a lens calibration target and you are exactly right - the focus shifts just a little at each half stop between F1 & F2. By F2, the focus point perfectly matches the rangefinder and from there on out, either there is no further focus shift, or it's hidden in the DOF. I'm not sure you would see the focus shift with a normal target (small print, etc), but you can see it with the angled calibration target.
I had considered sending the lens back, with the hope of getting one that is perfectly calibrated to the rangefinder at F1. After seeing the focus shift, I'm wondering if it's operating as designed and the RF is actually calibrated at F1.4 or 2? I'm curious about your thoughts, since you have quite a bit of experience with this lens. Otherwise, the lens seems perfectly centered and is acceptably sharp across the frame wide open at infinity. ...Show more →
Yes, that's normal operation. The lens is calibrated taking account focus shift and therefore it's usually perfect aligned with the rangefinder one stop down from wide open. If it would be perfectly calibrated at f/1, by f/2.8 the subject would be noticeably out of focus. With vintage lenses like the Leica 50/1 Noctilux for example this is even more apparent. It's really only an issue with fast and ultra fast lenses since the amount of aberration is higher wide open compared to slower lenses.
Of course, this is an issue with rangefinder focusing only. For those focusing with the help of LV, this is a non-issue.
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