Calibrating focus – adjustable focus ring---by Iurii Zronar

This detailed guide should work for lens that have bolts on focus ring. I’ve testedapproach on following lens so far :

       7artisans12mm F2.8

      7artisans35mm F1.2

MitakonZhongyi 35mm F0.95 Mark II Speedmaster

I’m using 7artisans 35mm F1.2 lens for this guide. Please feel free to contact mewith questions if you have another lens with bolts on focus ring and you’d liketo try calibrating it.

FirstI’ll define few terms that will be used later.

LensCore – inner glass frame that is moving during focusing

FocusRing – you rotate it for the focus, typically it has focus distance scale

LensBody – outer lens frame that connects to the camera

For lens focus calibration you will corresponding screwdriver that fits boltslocated on focus ring. In case of 7artisans 35mm F1.2 I’m using T3 screwdriver (but optimal should be T2).

Thereare typically two problems with misaligned focus:

Lenscan not focus to very far distance. For example you can focus on objects inrange of 0.35m – 50m, but everything further is still blurred, despite thefocus ring is rotated to maximal distance – infinity mark. To fix the issue youneed to collapse the Lens Core position (shift it toward the camera). So lenswill focus further for same focus ring marks.

Focusring overpassing infinity distance. It’s less critical issue, because you stillcan focus on any distant object. But if you rotate focus furhter everythingstart to blur. Most photographers like when most distant objects are sharp whenfocus ring is rotated to maximal distance – infinity mark. It allows blindlyrotate focus to maximum position and take a picture with 100% confidencedistant objects will be in focus. To fix the problem you need to extend theLens Core position (shift it toward the shooting object). So lens will focuscloser for same focus ring marks.

Fixlens that unable to focus on infinity – collapsing Lens Core position

Step1. Connect lens to your camera, rotate focus ring to it’s most far location –“Infinity” mark. Then gently unscrew bolts on the focus ring, make sure ring isnot rotated during that process and Lens Core is not moving. It is notnecessary to completely unscrew all bolts, few turns is usually enough to makefocus ring  loose.

Step 2. Nowgently rotate focus ring to some closer position, e.g. 5m. Make sure ring is rotating very loose, and Lens Core is not moving. For the better guide display I’m rotatingloose ring to 1m mark.

Step3. Gently secure all bolts on focus ring. Make sure ring is not rotated andLens Core is not moving.

Step4. After all bolts are secured rotate lens to infinity point, you will see thatLens Core is collapsing toward the camera more than before the adjustment.

Useyour camera and take some pictures on most wide lens aperture value. Now lensshould be able to focus much further. Try how full focusing range works  now. If it is still not focusing to infinity, repeat Steps 1 - 4. But if you can focusto infinity and now lens is overpassing it, then simply follow steps from  the second guide part below.

Fixoverpassing infinity – extending Lens Core position

Step1. Connect the lens to your camera, set the most wide aperture value (e.g. F1.2for 7artisans 35mm ), then find any small and contrast most distant object andprecisely focus on it. Take few shots and check that infinity area is perfectlyin focus.

Rememberthe focus ring position (or mark it with soft pencil on the lens body). Thengently lay down the camera on the flat surface, make sure focus ring keeps itsposition. Usually it will be very small rotation form the “infinity” mark. I’musing more dramatic adjustment for the guide so focused to 1m distance. You cansee that Lens Core got significantly extended here. In your case it will extendto very tiny amount.

NOTE:  lens with internal focusing have Lens Core hidden inside (eg. 7artisans 12mmF2.8), so you will not see any changes externally, just move to the next  step.

Step2. Gently unscrew all bolts on the focus ring. Make sure you don’t rotate focusring during that process. Also it’s not necessary to unscrew bolts completely,just do few turns for all of them until the focus ring become very loose.

Step3. Slowly rotate focus ring back to “infinity” mark. Make sure that Lens Coreis not collapsing and rotating effort is minimal.

Step 4. Accurately screw in all bolts on the focus ring, make sure ring does not moveduring that process.

Now your focusring “infinity” mark is adjusted to real infinity distance position.

If youaccidentally shifted Lens Core during securing focus ring and it is notfocusing to infinity, use the first guide part to make backward adjustment.