Why won't my Canon 400 mm prime lens focus?

[AnneEM]

Hello. I have a Canon 400 mm prime lens on a Canon Rebel camera. I am a wildlife photographer, so my camera has been used in some extreme temperatures. I have noticed lately that my camera does not always want to focus on wildlife. For instance, I was trying to take pictures of owls and while they showed up focused on the viewfinder and the auto focus was going off, they ended up not focused on my actual camera. This has been a problem for 3 months now. Sometimes it will focus, but half of the time it does not. I have never had this issue before. I use the P setting and my 400 mm lens a large majority of the time. I had my camera looked at very briefly at a shop and they found nothing obviously wrong with it. I'm not sure if its a problem with my lens or camera. I want to say it's my lens but I'm not sure because I only use the 400 since I photograph wildlife. Does this problem sound familiar to anyone?

[jimmy637]

Which Rebal are using the 400mm lens on and is your lens the 400mm f5.6?

[jrhoffman75]

1. Does it only happen with this lens?

2. If you go to LiveView and focus are the pictures sharp?

3. Are you in One Shot or AI Servo focus?

4. Can you post an image; preferably without stripping EXIF data?

[AnneEM]

It only happens with this lens. The pictures are not sharp on Liveview even though my focus is trying to work. I have been shotting in One Shot. The image below is an example. Lately, my images have been appearing even more unfocused than this one.

[jrhoffman75]

Are you in Program, One Shot and lens in AF?

Does the green focus dot light?

Did the lens ever work OK?

Do you have access to a different camera to try?

[Waddizzle]

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@AnneEM wrote:

It only happens with this lens. The pictures are not sharp on Liveview even though my focus is trying to work. I have been shotting in One Shot. The image below is an example. Lately, my images have been appearing even more unfocused than this one.

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It almost looks to me that the AF point that locked focus may not have been on the bird, and there's not a lot of contrast around the bird, either.  Does your post processing software display the focus points that acquired focus?

[AnneEM]

I have the Canon T1i and the 400 mm f5.6 lens is what I use.

[AnneEM]

No, I do not have that type of post processing software. Here is another picture with what the focus has been doing lately.

[ebiggs1]

AnnEm,

Hope this isn't going to hurt your feelings but I suspect this is a user error or technique problem.  But we do want to get to the solution. Right?

Here is what I want you to try next time. Use Tv or Av instead of P mode.  if you choose Av set the 400 to f5.6 and let the camera select the fastest SS it can.  If you choose Tv set the SS to 1/500 minimum.  Next set the Rebel to One shot and select just the center focus point. Turn the rest of the points off.  Lastly choose a fairly high ISO, say 400 or 800.

Try to get that single focus point on the head, better yet the eye, of the bird. Come back and show me what you get!

[AnneEM]

Ok. I'll try that mode. Feelings not hurt! I find it strange because I've had this lens for 4 years now and this is the first I'vve had this issue. I used it extensively in this spring and never had issues then.