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USM motor correct tension


I have a used 28-135. I did a repair on the lens where the zoom barrel was very wobblily. Got that fixed no problem but realized I should have cleaned all the dust partials out of the inside. So I pulled it back apart. In doing so the tension ring for the USM motor apparently came loose and it fell apart. I reassembled the motor but having no idea where it was originally adjusted to I had to adjust it for fill tension. So my $5 question is - is there a correct way to set that tension or am I left with trial and error.



"Canon C21-9931 Service Manual

Digital presentation of a Canon EF 28-135 3.5-5.6 IS USM lens service manual,"

If this is your lens. USCamera -dot- com sells a service manual for $12.99. No idea if that covers what you need.

John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, MX472, LR Classic

Thanks for that info. I downloaded that service manual. It appears the usm motors are factory set for tension. The manual does cover calibration but there is an interface that you must use to do so. Then all the calibration gets stored into the lens eprom. So looks like it will be some trial and error. Presently the focus will stick when you first power on after it sits for awhile but if you rotate the focus ring first it works fine so my guess is the wave ring tension is too high. This is assuming there needs to be a tension adjustment. The ring rotates counter clockwise to a stop position for full tension and I was under the impression that would be factory default and that tension would be engineered to be fully rotated. 

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