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Thread: help with auto focus

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    help with auto focus

    I bought my 550d with the twin lens kit just over 2 months ago and when I use the 55-250 lens I find that I have to manual focus, but with the 18-55 lens the auto focus works fine. At first I thought maybe it was because the objects I was trying to focus on were too close and the lens was confused but I have just been outside testing it on objects further away and it just can't auto focus. A couple of times after taking a shot on manual focus, I switched it to auto and it worked ok but then as soon I tried to take a shot of something else it wouldn't work. Is there something I am doing wrong??? Or is there something wrong with the lens or is it a fault with the camera. I am thinking I will have to take it back to the camera shop but just wanted to check here first. Any help is appreciated.
    Tania
    Insanity: doing the same thing over and over again and expecting different results. Albert Einstein


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    Finally got through to someone at the camera shop and sounds like a problem with the lens so problem at least diagnosed. Thanks anyway for reading.

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    In Training MarkChap's Avatar
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    Have never used the particular lens, but does the focus barrel turn when it auto focus's ??

    If it does maybe you are holding or touching it enough to prevent it from turning and achieving focus.

    I was going to suggest the AF/MF switch but seems you have tested that one
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    Thanks Mark, I think the barrel does turn, you can hear it whirring and see the image moving in and out, it just doesn't seem to know what to lock on. I also tested it in full auto so it could choose whatever focus point it wanted. Think I just got a dud. The guy at the shop did say something about if I left it on (I assume he means the camera) then something could have built up on something else and he would go over this thing (I can't remember exactly what he said because he might as well as been talking swahili) with his graphite pen and if that still doesn't fix the problem then will have to send the lens to canon and hopefully they will just replace it.

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    It's all about the Light!
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    @Tanz - I think he was talking about the contacts.
    I.e. the electrical connection between the body and the lens and cleaning those contacts.

    Graphite! No way - its conductive and can cause a short. A pencil eraser works.

    Yes, it sounds faulty.

    Do you have the latest firmware loaded? Sometimes that helps issues like this.
    I don't know enough about the 550D other that to suggest checking it.

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    Kym those words are definitely ringing some bells, so yep that must be what he is talking about. I have to wait for my husband to get home on the weekend as it is hopeless for me to try and take it in with my two children so I will get him to take it in and tell whoever to use a pencil eraser. As for the firmware I was actually looking at the canon site today and there was an update today (talk about coincidence), it was to fix a problem with the aperture changing if you were shooting video in manual exposure, I haven't actually downloaded it because I am a bit technically challenged and was too scared in case I somehow stuffed up my camera but maybe I will give it a go when the girls are in bed.

    Edit: I did check the firmware and mine is 1.0.6 and the new one is 1.0.8

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    I was referring to the outside, the part you grip when manually focusing, not the internals of the lens

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    Quote Originally Posted by MarkChap View Post
    I was referring to the outside, the part you grip when manually focusing, not the internals of the lens
    I just tried again to double check and yes the barrel turns.

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    I have noticed that at times auto focus lens are not happy focussing on low contrast items. I have been caught a few times with this and have switched to manual focus.
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    Ausphotography Veteran rwg717's Avatar
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    Sorry to report that I have been caught with a Canon EFS 17-85 IS lens which does much the same thing. In my case the person I bought it from admitted to the problem so I took posession at the agreed price (quite cheaply) with the hope it could be fixed cheaply.

    Unfortunately this did not turn out to be a cheap fix, a nice enough lens but a DUD! Thankfully you have warranty on your side and I would take full advantage of that ASAP
    Richard
    I've been wrong before!! Happy to have constructive criticism though.Gear used Canon 50D, 7D & 5DMkII plus expensive things hanging off their fronts and of course a "nifty fifty".

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    Thanks Richard. I have been playing with it heaps in the last few days trying to see if the problem is me and somehow my technique but I am taking it back on Monday and will see what they say.

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    Quote Originally Posted by stephendean View Post
    I have noticed that at times auto focus lens are not happy focussing on low contrast items. I have been caught a few times with this and have switched to manual focus.
    I was reading my manual again yesterday and noticed it says in there that there are instances where the auto focus might not work, including low contrast. I have tried on different objects at different lengths but nup, just doesn't want to work. I have found that if the object is already pretty much in focus then it might work.

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    I have that lens and it works great with auto focus spot on so I suspect yours has a fault. Actually for a "kit" lens it produces really sharp nice coloured pics.

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    Quote Originally Posted by Old Skool View Post
    I have that lens and it works great with auto focus spot on so I suspect yours has a fault. Actually for a "kit" lens it produces really sharp nice coloured pics.
    Thanks Russell, I have been using manual focus and am really happy with the shots so far and I prefer this lens to the 18-55 so I am very excited to think how much easier it is going to be to be able to use auto focus on it.

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