EF 28-105 f3.5-4.5 II USM - broken?

[phyliss_crowe]

<p>Just received this lens (Taiwan flavor; bought off eBay, reputable seller but No Return policy unless not as described) and have a question about it. </p>

<p>There is a skinny knurled plastic ring on it just above the AF/MF switch that moves the distance indicator in the window next to that switch. (Focus ring?) It moves the dial in the window from infinity to MACRO and back, and you can feel and hear when it "hits" both extremes of the scale. But the ring doesn't stop turning at either of those points. You can turn it around and around and around the lens as often as you want.</p>

<p>I Googled for the User Guide for this lens but came up empty.</p>

<p>Is this ring supposed to function like that or shouldn't it stop at each extreme of the scale? </p>

<p>My son's girlfriend needs it this weekend, and she lives a couple hours away at this time so it can't be tested until Thursday when she comes to visit. I know little of Canon and own Pentax so I can't test it myself. I so hope this isn't broken because it's cosmetically immaculate, and I really don't have time now to find another. I've already been disappointed once by a lovely Tokina 28-105 that turned out to have a disengaged focus ring, which is what I'm fearing is going on with this Canon, too. If so, is a repair costly and/or worth it? (Paid $150 for it; the cheapest one listed at the time.) (The Tokina was a gift so we might look into whether it's worth repairing.)</p>

<p>Also, is there any way to narrow down what year this Canon lens was produced?</p>

<p>TIA!</p>

[Jeremy Stein]

<p>I have this lens, and mine works exactly as you describe. There is no stop to prevent the ring from turning after it reaches the most or the least distant focus setting. Note that when you turn that ring the distance scale moves one way or the other to its maximum or minimum setting then moves no further, despite the movement of the ring. The ultrasonic focus motor is not solidly coupled to the distance scale, but is free to turn as you wish. This lets you touch up the lens focus after the camera has set what it believes is the correct focus.<br>

Your description sounds like the lens is working the way it is supposed to.</p>

[scott_ferris]

<p><em>"Also, is there any way to narrow down what year this Canon lens was produced?"</em><br>

<br></p><p>Most can be, but not all, <a href="http://www.the-digital-picture.com/Canon-

Lenses/Canon-Lens-Aging.aspx" _mce_href="http://www.the-digital-picture.com/Canon-Lenses/Canon-

Lens-Aging.aspx">read this for a full guide.</a></p>

[Marcus Ian]

<p>One of the better aspects of FTM (full time manual) USM AF -- not to worry, that's a good thing... It allows the user to override the focus anytime without messing w/ AF/MF switch. It's a godsend in questionable lighting on the zooms... </p>

[phyliss_crowe]

<p>Oh, thank you, both for the reassurance and your response!</p>

<p>Is it likely the Tokina I mentioned works the same way and isn't broken after all? She didn't really spend much time playing with it; just took a half dozen shots at Auto and pronounced it "soft" when the photos were bumped to 8 x 10. Perhaps she could've touched those images up with the focus ring, like with this Canon. There's no operational info out there about the Tokina, either.</p>

<p>Thanks again!</p>

[hjoseph7]

<p>"Perhaps she could've touched those images up with the focus ring, like with this Canon."<br>

I doubt that seriously.<br>

I have this lens and have owned it for 10 years. It is a very good Pro-sumer lens, but mine does not make any sounds at all when the dial turns from maximum to minimum focusing distance unless I really put my ear to the lens. If you think it's faulty a new replacment could be had for about $250. </p>

[HenryUK]

<p>This is entirely normal behaviour for this lens.</p>

<p>The manual focus ring turns the rotor of the ultrasonic motor. When the focus mechanism reaches the end of its travel, the manual focus ring slips. You can feel when the focus mechanism has reached its end stops, and if you listen carefully you can hear a slight clunk.</p>

<p>The lenses with the ring type ultrasonic motor have the rotor sandwiched between the motor stator and the manual focus ring. There is a clamping ring which compresses a wave spring that creates an axial force on the rotor. The clamping ring is held in position by friction and three spots of varinsh (usually pale blue). Over the years the clamping ring can come loose. The autofocus first becomes erratic and then stops working. Eventually the manual focus stops working as well.</p>

<p>It takes less than 30 minutes to strip the back end of the lens, tighten the clamping ring, add three spots of varnish and reassemble the lens.</p>

<p>If the manual focus ring feels tight and positive with no indication of skidding or lost motion the autofocus is probably OK too. The only way to test it is to put it on an EOS body and try it.</p>

<p>Henry</p>

[Marcus Ian]

<p>I don't know about the tokina, the one I had (an old 20-35/2.8) was somewhat 'ambiguous' when it came to precise focus, and the 'focus lock clutch' mechanism - The focus ring slid forward/back to engage/disengage the focus clutch, but only <em>if</em> the af/mf switch was in the right position and only<em> if</em> the focus placement was aligned (?) -- otherwise the AF would take forever(!) to find focus. <br>

I don't know of any Tokinas that have FTM focus (when AF is engaged) overide like the Canon does. The only 3rd party manufacturer who does (unless this has changed very recently) I believe is Sigma w/ their HSM lenses (only some of which, like Canon, which have FTM focus).</p>

<p>In a nutshell, IME, the tokina lock/unlock AF engage/disengage was just plain weird, and I never got a good feel for it before I ended up selling it, yours could have been broken, but it's just as likely that she didn't know how to engage the AF properly... especially if she just played w/ it for a couple mins.</p>

[phyliss_crowe]

<p>Very happy to hear good news about the Canon lens! Appreciate all the responses!</p>

<p>Girlfriend will be in town today with her 7D so will see how she likes it. And I'll get to watch how the Tokina behaves on-camera and see what it produces. too.</p>