Auto focusing
- Thread starter Hanmin147
- Start date
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.
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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. :bsmilie:
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. :bsmilie:
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.
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.
fatigue said: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. :bsmilie:
Woo... Okay that is why real experience is the way to go right?
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=c2xlM7bGHX0&feature=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
http://www.youtube.com/watch?v=c2xlM7bGHX0&feature=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
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.
daredevil123 said:
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?
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.
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
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