Repair - Focus calibration – lens with adjustable focus ring

This repair guide shows how to correct focus precision of manual focus lens with adjustable focus ring.

This method should work well if lens manual focus ring has bolts on it, and loosening that bolts releasing focus ring to be rotated without changing focus. 

I’ve tested approach on following lens so far, or got confirmation from other lens owners:

7artisans 7.5mm F2.8

7artisans 12mm F2.8

7artisans 35mm F1.2

Mitakon Zhong Yi 25mm F0.95 Speedmaster

Mitakon Zhong Yi 35mm F0.95 Speedmaster Mark II

Mitakon Zhong Yi 50mm F0.95 Speedmaster Mark II “Dark Knight”


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



First I’ll define few terms that will be used later.


  • Lens Core – inner glass frame that is moving during focusing
  • Focus Ring – you rotate it for the focus, typically it has focus distance scale
  • Lens Body – outer lens frame that connects to the camera





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


There are typically two problems with misaligned focus:


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



  • Focus ring overpassing infinity distance. It’s less critical issue, because you still can focus on any distant object. But if you rotate focus further everything start to blur. Most photographers like when most distant objects are sharp when focus ring is rotated to maximal distance – infinity mark. It allows blindly rotate focus to maximum position and take a picture with 100% confidence distant objects will be in focus. To fix the problem you need to extend the Lens Core position (shift it toward the shooting object). So lens will focus closer for same focus ring marks



Fix lens that unable to focus on infinity – collapsing Lens Core position

Step 1. 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 is not rotated during that process and Lens Core is not moving. It is not necessary to completely unscrew all bolts, few turns is usually enough to make focus ring loose.





Step 2. Now gently 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 rotating loose ring to 1m mark.



Step 3. Gently secure all bolts on focus ring. Make sure ring is not rotated and Lens Core is not moving.



Step 4. After all bolts are secured rotate lens to infinity point, you will see that Lens Core is collapsing toward the camera more than before the adjustment.



Use your camera and take some pictures on most wide lens aperture value. Now lens should 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 focus to infinity and now lens is overpassing it, then simply follow steps from the second guide part below.


Fix overpassing infinity – extending Lens Core position

Step 1. Connect the lens to your camera, set the most wide aperture value (e.g. F1.2 for 7artisans 35mm ), then find any small and contrast most distant object and precisely focus on it. Take few shots and check that infinity area is perfectly in focus.


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




NOTE: lens with internal focusing have Lens Core hidden inside (eg. 7artisans 12mm F2.8), so you will not see any changes externally, just move to the next step.


Step 2. Gently unscrew all bolts on the focus ring. Make sure you don’t rotate focus ring 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.




Step 3. Slowly rotate focus ring back to “infinity” mark. Make sure that Lens Core is not collapsing and rotating effort is minimal.



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


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


If you accidentally shifted Lens Core during securing focus ring and it is not focusing to infinity, use the first guide part to make backward adjustment.

2 Comments

  1. This comment has been removed by the author.

    ReplyDelete
    Replies
    1. It worked perfectly on my TTArtisan 50mm f/1.2! Thank you!

      Delete
Post a Comment
Previous Post Next Post