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Russell H.
Russell H., Technician
Category: Digital Cameras
Satisfied Customers: 12237
Experience:  Working with digital cameras & questions for nearly 8 years.
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The autofocus on my Canon 400f 5.6 L lens is not working properly.

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The autofocus on my Canon 400f 5.6 L lens is not working properly. Sometimes it jams up completely,other times itmoves backwards & forwards but does not focus, generally the auto focus has gone from fast to very very slow. Any ideas?
Hi, thank you for contacting My name isXXXXX will do my best to provide the right answer to your question.

I am assuming below that there is only one camera that this problem shows up with. (If it shows up exactly the same regardless of all cameras on which this lens is used, disregard the questions about the camera and its battery.)

Has the battery previously worked in the camera?

How long has the battery been used in the camera? if for over a year of moderate (charge-and-discharge) usage, or for over 9 months of intensive and continuous charge-discharge usage, I advise replacing the battery, with another battery rated for power-delivery sufficient for this model.

How old is the camera? in months or years since you bought it.

Has the camera been dropped or otherwise subjected to mechanical shock(s) in its lifetime?
Has the camera been operated in or subjected to, temperatures below 32 degrees F (freezing point) or above about 100 degrees F ?
Has it ever been subjected to a humidity higher than 85 % ? or gotten wet?
Has the lens been used in a gritty or sandy environment, such as a sandpit, a beach or seaside, a construction site, etc.?

Customer: replied 4 years ago.

No! It isn't the camera. I have tried the lens on a Canon 7D of my own, a Canon 50D mine. Also my friend's 7D & it works just as badly on them all. So it is the lens auto-focus that is not working properly. I use the lens to photograph flying birds so it is essential that the AF works fast & is accurate. I think I am resigned to the fact that I either have to pay a fortune to have it repaired or buy a new one.

You wouldn't have to pay to have it repaired, if it were still within the warranty period.


Maybe I asked this before, but was the lens ever operated in a gritty sandy or dusty environment ?

Customer: replied 4 years ago.

No again.It is quite an old lens. January 2006 it was manufactured. It has had a great deal of use since then. Thanks for your advice but I think I will first try to get it repaired - if the cost is reasonable. If not I will have to replace. Cheers.

Would you like to have it repaired by a Canon shop?

If so, the list is here, for UK locations:

and then in the Product Group section, select 'Lenses' and click on the Search button.
Customer: replied 4 years ago.

Cheers XXXXX XXXXX is a great help. I wasn't too sure where to contact Canon Services. I have a friend who has used them for repairs, but he is away in South America for a few weeks. I'll have a proper look tomorrow. Glad I contacted you. If there is any way I can tell Justanswer that I am very satisfied with your help I will do.

Best Wishes

Good luck with Canon Services.

Thank you for asking your question here at Feel welcome to stop back anytime to ask any other question you may need to ask an Expert in any one of our numerous categories.
I hope that my recommendation to a Canon UK Services shop is going well.

Thank you for consulting
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