The Binocular Sky


Re-setting the Right Eyepiece Dioptre

Kunming 15x70

Budget Kunming Optical Industries 15x70
(Strathspey, Revelation, etc.)

The Problem

It is often the case that the right eyepiece dioptre adjustment is poorly set. People whose eyes are similar, often need to adjust the right eyepiece close to the end of its range in one direction or the other, when they would have expecteed it to be approximately central. This situation is worse with a user whose eyes are different by a dioptre or more; in this circumstance, a badly adjusted right eyepiece may prevent the user from being able to focus both eyes.

The remedies can be simple:

The Solution

The only tool you need is a small flat-head screwdriver.

  1. Carefully prise off the rubber eyecap; it may be held in place by a few smears of poor quality contact adhesive, but there is no need to re-glue it when you replace it. You will probably uncover some of the sticky substance that the manufacturer has substituted for a decent lubricant grease – do your best not to transfer any onto the optics.

  2. grubscrew
  3. Locate and slacken the three grubscrews (a.k.a. "set-screws" if you are west of the Atlantic) that are located under the flange.

  4. Rotate the eyepiece as far as it will go in the direction you need to extend the rotation.

  5. Right Eyepiece Dioptre Mechanism
  6. Lift off off the outer rotating part to reveal the adjustment mechanism. Note the splines on the rotating lens housing and the stops on the fixed part.

    WARNING: In some incarnations of this binocular, the outer rotating part is cemented to the inner rotating part and will not easily lift off.

    If it is not cemented, removal takes no more force than it does to rotate the mechanism.

    If it is cemented, it can still be removed with a lot of force and extreme care but YOU ARE RISKING DAMAGE TO THE BINOCULAR. If it is cemented, there will be no splines and you will need to re-cement it once you have adjusted it to your liking. Take care not to get adhesive onto the eyepiece or into the threads of the adjustment mechanism.

  7. Note the lug and splines in the rotating part that you removed in the previous step. Replace this part so that the lug is mid-way between the stops. Test to see if you can obtain focus with both eyes. If you cannot, repeat steps 3-5, and obtain the correct adjustment by trial and improvement.

  8. Once you are satisfied, reassemble the eyepiece in the reverse order to disassembly. Remember to tighten, but do not overtighten, the grubscrews. Replace the rubber eyecap so that the central dioptre mark aligns with the fiducial mark when the right eyepiece is correctly focused for you.

NB: I offer this advice in good faith, but you follow this description at your own risk. I cannot be held liable if you damage your binocular, yourself, or anything else, as a consequence of attempting procedures that I offer on this web site.