Broken plain bearings: When a zoom lens suddenly stops moving

[Andreas Thaler]

Zoom lenses with manual settings are adjusted to change their focal length using either a rotating ring or a tube. To allow the lens to extend or retract, the moving parts slide along plain bearings in guide slots.

These plain bearings

are often made of plastic, which can break after decades of use. The broken pieces can then get stuck in the guide slots and block the zoom mechanism.

The only solution is

to disassemble the zoom lens and replace the plain bearings. To do this, their metal retaining screws must be unscrewed. If force is applied, these screws can also break, which complicates the repair.

Unfortunately

there is no standard size for plain bearings, meaning that different sizes are used in zoom lenses. Sometimes, however, you get lucky, and plain bearings from other zoom lenses can be used, as is the case here:

Tokina RMC 25-50/4: Zoom blockage fixed, plain bearings replaced, helicoids greased

Buying used zoom lenses

I therefore recommend checking that the zoom mechanism runs smoothly when buying used.

Jerky or stuttering movements indicate that the plain bearings are already damaged. However, the problem can also arise suddenly without warning. Heavily used zoom lenses are particularly prone to this wear and tear.

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A word of caution

Please keep in mind that you’ll be using highly flammable solvents for service work, and their fumes are harmful to your health. Soldering also produces fumes that should not be inhaled. Dangerous high voltages can be present when handling electronics, especially in conjunction with electronic flash units and mains. Therefore, familiarize yourself with the safety regulations beforehand and ensure your safety. Depending on the activity, protective gear may be advisable.

All information provided without guarantee and use at your own risk.

Acknowledgments

Without the work of Master Larry Lyells, in particular, we wouldn’t have the detailed technical information we need today for service/repair of SLRs.

The SPT Journal and The Camera Craftsman, which he helped shape significantly as an author, and which contain all the necessary information and instructions are available for a fee through Learn Camera Repair.

We owe our access to them to Eugene Pate, the founder of Learn Camera Repair.

 

[mshchem]

As a kid I wanted Nikon zoom lenses so bad. I remember a friend who had a 43-86mm f3.5. I thought it was the coolest thing ever! A rich kid. Last time I saw him he was buying a Nikon Z7, he has his own airplane

 

[koraks]

Looks like replacement parts could be fairly easily 3D printed, or even better, milled. Both of these options are now quite readily accessible to the general public.

 

[Andreas Thaler]

One challenge is that you have to completely disassemble the zoom lens to do this; the screws on the slide bearings are sometimes stuck, and then everything has to be readjusted.

Instructions for this are rare—apart from those by Richard Haw for Nikkor lenses. The SPT Journal covers only a few zoom lenses. So it’s not an easy task.