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Thread: Auto focusing

  1. #21
    Moderator daredevil123's Avatar
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    Default Re: Auto focusing

    Could be a problem with the lens, not the camera.

  2. #22
    Senior Member fatigue's Avatar
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    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    Sorry for the confusion, let me clarify. When shooting a still subject, the camera fails to focus on single shot mode. Meaning that it keeps going back and forth trying to focus. It's an old camera so I suspect that is the problem.
    Sorry again for the trouble caused. Thanks so much for the help.
    Isolating the problem by using another lens could help you identify if it's the lens or the camera that's causing the problem
    But based on this info, I suspect the problem is on your lens.
    I'm not an expert but I have fixed quite a number of this lens with the same problem.
    The usual culprit, the Giant Magnetoresistance (GMR). This part senses the movement of the motor (USM).
    If the signal from the GMR is weak, the microprocessor (uP)thinks the motor is not turning so the uP will keep sending a signal and the USM will just turn back and forth.

    Cleaning the GMR and magnetic strip usually solves the problem.
    Last edited by fatigue; 4th October 2011 at 05:57 PM.
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  3. #23
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    Quote Originally Posted by fatigue

    Isolating the problem by using another lens could help you identify if it's the lens or the camera
    But based on this info, I suspect the problem is with your lens.
    I'm not an expert but I have fixed quite a number of this lens with the same problem.
    The usual culprit, the Giant Magnetoresistance (GMR). This part senses the movement of the motor (USM).
    If the signal from the GMR is weak, the microprocessor (uP)thinks the motor is not turning so the uP will keep sending a signal and the USM will just turn back and forth.

    Cleaning the GMR and magnetic strip usually solves the problem.
    Where is the GMR and magnetic strip located?

  4. #24
    Senior Member fatigue's Avatar
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    Default Re: Auto focusing

    Quote Originally Posted by David Kwok View Post
    I won't say I'm well read, just that I'm a science person. Base on what TS described, if the issue is because of focusing distance or focus motor, then how can he possibly achieve focus in AF-C mode ? So I rule out the possibility that it's due to misuse of the equipment. In the last description, TS mentioned that in AF-S mode and the lens is hunting up and down to attempt focus. One possibility is there is nothing to focus such as a lens cap on or excessive dim lighting, the other is focus point is not set on something to focus on. Now the first is out because TS managed to focus in AF-C, the 2nd is unlikely because even if TS doesn't know how to use DSLR, it would at least catch something in the background or foreground to focus, instead of going back and forth.

    Next is TS did mentioned he is not new to DSLR, so I'm not going to assume he is totally unaware that he need to point the focus point at the subject or too close to focus. The clue that allow me to make that conclusion is he managed to focus using AF-C and not AF-S. I have did a quick lookup on Canon 400D and it did equip with phase detection feature and seemingly coincide with the symptoms that he is describing.

    Of course, I'm not totally convinced yet. Hence I ask him to check if there is anything blocking light between the lens, mirror and the top translucent thingie which is suppose to lead to the AF unit.

    As a disclaimer, I don't repair cameras and I don't take them apart too. Not that wealthy to do something like this.

    I do like to read up on photography and its related technicalities hence I am quite informed in how camera does focusing for both phase detection and contrast detection.
    I'm impressed

    My disclaimer: I'm not an expert but I do repair cameras and I do take them apart too. I'm definitely not wealthy so I have to do something like this.
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  5. #25
    Senior Member fatigue's Avatar
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    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    Where is the GMR and magnetic strip located?
    Sad to say, it's inside the lens. The USM assembly need to be dismantled.
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  6. #26
    Member Hanmin147's Avatar
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    Quote Originally Posted by fatigue
    Sad to say, it's inside the lens. The USM assembly need to be dismantled.
    Wow.. Thats not good. I detached the lens from my camera to look and there was nothing blocking it whatsoever. Looks like manual focus is the way to go.

  7. #27
    Moderator daredevil123's Avatar
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    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    Wow.. Thats not good. I detached the lens from my camera to look and there was nothing blocking it whatsoever. Looks like manual focus is the way to go.
    Looks like you do not understand bro fatigue's comment. It is best you send the lens into the service centre if still under warranty. If not, you can also send it into service center, or look for an alternative repair person, like fatigue.

  8. #28

    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    Wow.. Thats not good. I detached the lens from my camera to look and there was nothing blocking it whatsoever. Looks like manual focus is the way to go.
    You won't see it by looking into the lens. The USM assembly is not a lens, it's something you won't see. Either bring the lens for servicing, or, considring how old it is, you may gat a better bargain buying a cheap second-hand kit lens from the BnS.
    Alpha

  9. #29

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    Quote Originally Posted by fatigue

    I'm impressed

    My disclaimer: I'm not an expert but I do repair cameras and I do take them apart too. I'm definitely not wealthy so I have to do something like this.
    Woo... Okay that is why real experience is the way to go right?
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  10. #30
    Senior Member fatigue's Avatar
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    Default Re: Auto focusing

    Someone posted this video in youtube. It's a different fix but it shows how to dismantle the USM assembly.
    http://www.youtube.com/watch?v=c2xlM...ature=youtu.be

    The USM assembly is the part he dismantled at 9min 34sec
    After this step,it's a different procedure. You need to dismantle the bottom part of the USM assembly to access the GMR.
    There's a few screws and need to dismantle the PCB as well.

    Take note:
    1. be very extra careful with the flexible cables, they break easily.
    2. Not suppose to touch the USM with bare hands, this will result in noisy motor operation

    If you're not confident enough, send it to service center
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  11. #31
    Member Hanmin147's Avatar
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    Well it is an old camera and lens and I am looking to upgrade when SITEX comes this year end. Thanks for all the help guys
    Last edited by Hanmin147; 4th October 2011 at 08:20 PM.

  12. #32
    Moderator daredevil123's Avatar
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    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    Well it is an old camera and lens and I am looking to upgrade when SITEX comes this year end. Thanks for all the help guys
    The lens is a good one. You can still use it on a new Canon body. Or even sell it in BnS to help fund for your upgrade in the future. But make sure you get it fixed first before you sell it.

    BTW, SITEX and other computer shows are lousy places to get a camera. Prices are much higher than everyday prices you can get in the reputable stores any day.

  13. #33
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    Quote Originally Posted by daredevil123

    The lens is a good one. You can still use it on a new Canon body. Or even sell it in BnS to help fund for your upgrade in the future. But make sure you get it fixed first before you sell it.

    BTW, SITEX and other computer shows are lousy places to get a camera. Prices are much higher than everyday prices you can get in the reputable stores any day.

    Thanks for the heads up. I will definitely try to find the problem. Heading over to my friend's place after my exams to test out lens and body. Gonna use my lens on his canon 600D and his lens on my canon 400D. This would definitely isolate the problem and I would try to trouble shoot.


    From what i saw COMEX gives you plenty of free gifts when you get a camera like 600D. Can you recommend some places to me for buying a camera?

  14. #34

    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    From what i saw COMEX gives you plenty of free gifts when you get a camera like 600D. Can you recommend some places to me for buying a camera?
    Thjey are not free. You pay $200 more than you would outside of Comex for maybe $100 worth of "freebies", of which half are worthless.

    There is NOTHING free.

    If you want to know where to buy, we have a priceguides section for a reason.
    Alpha

  15. #35
    Moderator daredevil123's Avatar
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    Default Re: Auto focusing

    Quote Originally Posted by Hanmin147 View Post
    Thanks for the heads up. I will definitely try to find the problem. Heading over to my friend's place after my exams to test out lens and body. Gonna use my lens on his canon 600D and his lens on my canon 400D. This would definitely isolate the problem and I would try to trouble shoot.


    From what i saw COMEX gives you plenty of free gifts when you get a camera like 600D. Can you recommend some places to me for buying a camera?
    Yes, "free gifts" and the total package price is $200-300 more. And those free gifts, most of the time, are offered by the manufacturer (ie Canon in your case) anyway. So you buy from any normal store, most of the times you can still redeem the gifts. And some of the gifts are useless, bag that cost $40, Tripod that is flimsy (cost around $20), and cleaning kit (cost price $3-$5).

    There is no free lunch in this world. The only good deals at computer shows, are computers and printers only.

    As for reference on street prices and places look here: http://www.clubsnap.com/forums/forums/124-Price-Guides
    Last edited by daredevil123; 5th October 2011 at 01:04 AM.

  16. #36
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    Thanks for all your help guys

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