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Cameron, Camera Technician
Category: Digital Cameras
Satisfied Customers: 3943
Experience:  Tech Business Owner/Photographer
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My Tamron 18-400lens has issues with the auto focus when I

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Hi, my Tamron 18-400lens has issues with the auto focus when I extend the lens over 100mm the Fstop goes to F00
JA: Has there been any damage to your camera recently (e.g. from dropping or from dirt getting in the lens)?
Customer: no nothing at all. Was doing some manual focusing the evening before abs the photos were good. Then in the morning when I changed back to AF, this problem arose. I have tried the lens in my other camera and it’s the same.
JA: What kind of battery does your camera use? Have you tried taking out the battery and replacing it?
Customer: I have also used other lens in both cameras and they are ok.
JA: Anything else you want the Camera Expert to know before I connect you?
Customer: the two canons use different batteries, but I have not tried that.
Customer: replied 9 days ago.
Customer: replied 9 days ago.
Still waiting on help

Hello there! I hope you’re doing well so far today! My name is Cameron & I am a tech expert here with JustAnswer, an independent, paid support website. As an expert, I have 10+ years of experience helping people learn, use, and fix all of their electronics, and I’ve helped over 5,000 different customers throughout this time!

I know these kinds of issue with technology can be really frustrating, especially when it seems there is no solution. I am sorry you have to deal with this, but I’m here to help! I just want to help you as best as I possibly can to try and find a solution, and if we can’t find a solution, I can at least provide you with the best steps to take next!

I appreciate the information you've provided so far, that helps people like me sift through all possibilities and variables faster! What I can say here about your issue is that if this is occurring on multiple camera bodies, then you can obviously narrow the issue down to the lens.

Now without being able to take a look at it in person, I can attest that these types of issues with what you're experiencing tend to fall on the side of an error with the lens contacts, the smaller, sphere-shaped metal pieces that are on the lens and match up with matching pieces on the camera body. When measurements start to become skewed or not working, it's almost always the lens contacts as the issue.

You can try to wipe them clean with a microfiber cloth, but it's very possible the contacts are malfunctioning here and will require at least an in-person consultation from a repair professional, if not a full repair depending on what the professional is able to determine.

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