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?

[jrhoffman75]

Always worked and now it doesn't. Seems like a lens problem.

[ebiggs1]

"Seems like a lens problem."

Perhaps so, but other factors must be resolved first before we draw that conclusion.

[jrhoffman75]

Studying the image of the small bird it doesn't look like anything else hijacked the focus. The bird is the most sharp item in the image.

As suggested, single center point focus should narrow down problem.

[diverhank]

As suggested, there is a very good chance that it is the user problems. I'm not saying that it is but to eliminate that, you need to make sure of a few things.

1. You need to have fast shutter speeds. To shoot birds with this lens, never shoot slower than 1/1000 or you will risk soft images that can be mistaken for poor focus.

2. Shoot with P does not guarantee fast shutter so use Tv instead with auto ISO.  You might have had ample light before so the speed was high so the pics looked good... but good light are not always possible.

[jrhoffman75]

If you aren't using LiveView the sensor plays no part in focusing. If you got a lot of dust in the mirror chamber it is possible that the AF submirror is coated. I put that low on the list though.

[ebiggs1]

Whatever works.

[AnneEM]

Thank you again, everyone for the constructive feedback! I am happy to say that I have in fact found the solution to the focusing issue.

Basically, I was not convinced that it was user error. (Sorry) Simply due to the fact that I have shot handheld with a relatively slow SS on non-ideal weather days before and my pictures have been fine. Yes, I have shot handheld with a SS of 1/400 or 1/500 with my 400 mm fixed lens before and my pictures were fine up until recently. For example, I have three sharp images below with handheld technique and low SS.

GREG with 1/500 SS

SNEG with SS 1/500

PUGA with SS 1/500

This is why I had a difficult time understanding that motion was the issue with the camera. Yes, it very well could have been a factor. (I will try faster SS in the future!) But I still had a hard time understanding why it would blur my photos this consistently after being able to take perfectly fine photos for 3 plus years. So I took it into a Canon Certified Repair Shop. It was looked at by staff in a backroom for 25 minutes. They came back and told me that my camera was back focusing and that something in the camera was bumped out of place, which is understandable because I was using my camera intensively in Florida. When testing it, they used their own lens so it was not my lens at fault, but my camera body itself. So now, it is getting repaired.

Thank you again for the help.

[TTMartin]

---

@AnneEM wrote:

Thank you again, everyone for the constructive feedback! I am happy to say that I have in fact found the solution to the focusing issue.

Basically, I was not convinced that it was user error. (Sorry) Simply due to the fact that I have shot handheld with a relatively slow SS on non-ideal weather days before and my pictures have been fine. Yes, I have shot handheld with a SS of 1/400 or 1/500 with my 400 mm fixed lens before and my pictures were fine up until recently. For example, I have three sharp images below with handheld technique and low SS.

GREG with 1/500 SS

SNEG with SS 1/500

PUGA with SS 1/500

This is why I had a difficult time understanding that motion was the issue with the camera. Yes, it very well could have been a factor. (I will try faster SS in the future!) But I still had a hard time understanding why it would blur my photos this consistently after being able to take perfectly fine photos for 3 plus years. So I took it into a Canon Certified Repair Shop. It was looked at by staff in a backroom for 25 minutes. They came back and told me that my camera was back focusing and that something in the camera was bumped out of place, which is understandable because I was using my camera intensively in Florida. When testing it, they used their own lens so it was not my lens at fault, but my camera body itself. So now, it is getting repaired.

Thank you again for the help.

---

It makes sense that something was wrong inside your camera. There was something very funky going on in the bokeh of your camera that wasn't there on your fiance's camera.

That's why I thought it might have been some sort of contamination on your sensor. But, the anti-aliasing filter being loose makes sense.

[ebiggs1]

"Basically, I was not convinced that it was user error."

I am not going to belabor the point if you have a solution but back focusing only puts the focus point in a slightly different spot. It does not blur the entire photo.  In other words something in the shot should be in focus.  The problem is more apparent at wider apertures than smaller ones. It may disappear completely as the aperture gets very small.