Showing results for 
Show  only  | Search instead for 
Did you mean: 

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


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?




I can't argue against any of what you say. Also the difference between Tv and Av just shifts the priority.  It does not eliminate the problem.  However, when a person is trying to get at the problem and doesn't really know or understand where it is, the variables must be limited.  Agreed?

In her situation she needs to be in all, full, manual mode and the lens in MF.  She needs a stationary target and a solid camera mount.


Personally I am too old school to use very much of what the modern DSLR can offer.  Auto ISO is one of them. I never use it.  I want it fixed at where I want it.  Av fixes the lens at f5.6 and I do let the camera select the fastest SS.  If it can't, the photo may not be possible with normal procedures.  All camera/lens combos have their limits!


From the photos I looked at, I think the camera and the 400mm lens is fine.  I believe it to be a technique issue.  But the testing without the variables will confirm or reject that theory.  If she wants to continue to try to shoot the birds, I offer the Av, camera select SS and fixed ISO @ 400.  That is what I would do.

EOS 1DX and 1D Mk IV and less lenses then before!



It is possible even for and old has been like me to get reasonably sharp photos with less than perfect technique.  This is hand held with the big Siggy at 600mm.  Av fixed at wide open, SS was 1/640 selected by the Mk IV and of course the ISO of 400.



A more reasonable SS might be in the 1/1000 range and higher for this combo.


A trip to the Omaha zoo with just snapshots in mind, grandkids were with me, this was the Mk IV with my 70-200 @ 200mm.

SS was selected of 1/250 and again ISO of 400.  To get a sharp photo with 200mm is going to be a lot easier than with 600mm or even 400mm.   That is why I suspect her crane is much better.



EOS 1DX and 1D Mk IV and less lenses then before!



BTW, both of those are pretty aggressive crops.  That possibility is one reason I don't use or like Auto ISO.  I want to know where it is.

EOS 1DX and 1D Mk IV and less lenses then before!

@ebiggs1 wrote:



BTW, both of those are pretty aggressive crops.  That possibility is one reason I don't use or like Auto ISO.  I want to know where it is.

Thanks for the explanation.  I guess I don't disagree with anything you said.  


Even though I'm no pro by any standards, most of the time I shoot in full manual (Av, Tv, ISO) except when shooting birds in flight where I use M with Auto ISO.  My favorite BIF action is to track and take pictures of  an osprey loitering 200ft above a lake, ocassionally swooping down into the water and emerging with a fish.  The whole sequence takes about 2 or 3 seconds flat and the light conditions change so dramatically, a fixed ISO would spell disaster (I had many ruined shots to show for).  An Osprey sequence like that only comes like twice a year so missing a shot is always cause for getting drunk to get rid of the sorrow :).  Like Waddizzle, I limit the upper ISO to something I can live it and auto ISO works really well, especially my 7D Mark II allows me to do exposure compensation in M mode so I can compensate for the darker bird.

Diverhank's photos on Flickr

Food for thought.  When I use Auto ISO, I set an upper ISO limit in the menus.  No need to set it manually.  My preference is to keep an eyeball on the SS and let camera figure out ISO, especially under widely varying light conditions. 


One quirk with letting the camera determine SS or ISO, though, it makes exposure compensation misbehave.

"The right mouse button is your friend."

@AnneEM wrote:

Thank you everyone for your contributions. And sorry for the delay in response. I just now had time to get out and try out the different settings on my camera.


Unfortunately, the Tv mode did not work well on my camera. In fact, I did a little experiment. I tried the same exact settings with my lens on two different cameras, both of which are Canon Rebals. ( Mine is a t1i and my fiance's is a t3i). One person took pictures of the same subjects with the same shutter speed on Tv mode. We picked a shutter speed of 1/2500 and an auto ISO. Everything else was the same other than the camera body change. We even use a flat platform to act as a tripod to minimize shaking.


First, I'll present you a photo of my attempt to take a picture of a bird on the settings suggested. Link here: GREG on Tv mode


The shutter speed was 1/500, and the bird was not moving. I usually take images of birds when they are relatively stationary. I don't take flying images often. The ISO was auto and my camera chose 100. This was at 400 mm.


This image frustrated me, so that's when I started the experiment. Here are the results:

Tree on t3i

Tree on t1i


If you zoom in, you'll notice that the tree is sharper on my fiance's camera (t3i) than mine. My camera chose an ISO of 1000 while his chose an ISO of 800.


In the past, my camera has chosen decent shutter speeds on its own with P mode. For instance, this picture of sandhill cranes came out well and it was on P. (Link here: Sandhill Crane Family) The shutter speed for that image was 1/2000 with an ISO of 800. So it does seem fishy that P has not worked for me at all recently when it used to be fine.



Take your camera and lens, and stop it down to f/32 and take a picture of clear blue sky. It looks to me like your sensor needs cleaning. 



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!

EOS 1DX and 1D Mk IV and less lenses then before!

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.


The problem just might be using P mode.  Sometimes, maybe most of the time, it will select correct settings.  However, sometimes it won't.  Anything except One Shot and a single focus point can have the same result.  It may select the correct one or it may not.  If you do all the selecting you eliminate that issue.

EOS 1DX and 1D Mk IV and less lenses then before!

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?
John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, Pixma TR8620a, LR Classic