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?

[diverhank]

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@AnneEM wrote:

The only thing that may have changed is dust that got in my sensor. I was using my lens a lot in Florida and one day I noticed a lot of spots in my images. After that, I noticed that it was harder to get good focus. I just got my sensor cleaned the other day, but the people at the shop told me that a dirty sensor is likely not the issue. I have no been able to experiment with my camera since I got it cleaned due to weather.

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The AF mechanism is separate from the sensor so that would not be the factor.

Out of curiosity, what were the Av, shutter speed and ISO values for the two pictures you posted? Frankly I don't think those two looked that bad...they look more to me like motion blur rather than focus blur (due to lack of focus).

Just to rule factors out, even though both of these are highly unlikely.

1. check the menu for AFMA (autofocus micro-adjustment) and make sure it's not enabled...you or someone might have inadvertently enter in a correction value that is not needed.  I think your camera has this function. If not don't worry about it.

2. Check and make sure that you or someone hadn't inadvertently disable the AF function for the shutter button.  One way to quickly verify is to switch the camera mode to the green square.  In that mode, the AF function will be linked to the shutter button.

[ebiggs1]

"... they look more to me like motion blur rather than focus blur (due to lack of focus)."

Bingo.  This is/was my diagnoses, too.  I don't think there is anything wrong with camera or lens.  It is technique related.

"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."

[jrhoffman75]

[diverhank]

Thank you John for  the exif info. I'm surprised you can extract info out of pictures posted here.  In this shot, which is the better of the two, 1/400 is very iffy for this lens which has no IS.  The sharpness is what I'd expect at this shutter speed.  In my circles, there was this one photog whose 400/5.6 pictures would consistently beat mine in sharpness...turns out he shot everything at 1/4000 while mine was usually 1/1000 or 1/2000.  The term "faster is better" really applies herein.

To the OP, you need to control your Tv, among other things,  for wild-life shots and get out of P mode.  Follow the great advices on this thread.

Here's a shot taken with the 7DII, 400mm f/5.6L @ 1/2000, f/5.6, ISO 400 - M mode with Auto ISO

[jrhoffman75]

I see that camera is set for AI Focus. Perhaps camera is sensing some shake and switching to AI Servo. I would suggest selecting One Shot.

[ScottyP]

Yes, too slow a shutter, and since this is a crop body, her 400mm lens should need 400 X 1.6 = 640, so 1/640 minimum and that assumes good stable handholding.  Just to be safe, and to deal with birdy motion blur I'd say she should have at least 1/1000 shutter speed. Outside in the daylight why not make it 1/2000?

[AnneEM]

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.

[jrhoffman75]

Slight differences in exposure metering are not unexpected. ISO 1000 vs ISO 800 is ⅓ of a stop. Plus It's also possible that the exposure algorithms are different in the two cameras. 

I am at a loss. The T1i/T3i comparison seems to rule out the lens, but your viewfinder/LiveView focus test seems to rule out the camera. 

[ebiggs1]

OK here is the facts.  What you have done is really useless.  The only way to conduct a real meaningful test it to control all aspects of the test. This means a tripod a stationary target and lighting conditions.  A test target can be d/l form the ole inner web.  You can 't use settings like 'auto ISO' either.  Full manual control is best.

I really believe you guys are not holding the camera still enough.  The one Greg took has nothing in focus. That looks like motion blur from the camera.  If you are going to try non-tripod shots with a 400mm lens on a crop body camera, 1/1000 is the slowest Tv you should use.  However, this dose not guarantee a sharp photo.  It is simply one recommendation. When you are trying to figure out what is going on, you must eliminate every possible variance.

My personal way to use a tele like you want to do, is to use Av, not Tv, BTW.  If you fix your lens to f5.6 (Av), your T1i/T3i will select the fastest SS it can.  Your ISO should be 400 again my personal preference.  Not auto ISO.

Of course you need to do this type shooting on good daylighted days or good brightly overcast days.  If it is dark or early morning or late evening things are going to be more challenging.

On the sandhill crane family you used a 250mm lens.  It will be a lot easier to get a sharp photo with it vs the 400mm.

Set up a test where you control everything.

[diverhank]

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@ebiggs1 wrote:

My personal way to use a tele like you want to do, is to use Av, not Tv, BTW.  If you fix your lens to f5.6 (Av), your T1i/T3i will select the fastest SS it can.  Your ISO should be 400 again my personal preference.  Not auto ISO.

Of course you need to do this type shooting on good daylighted days or good brightly overcast days.  If it is dark or early morning or late evening things are going to be more challenging.

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Ebiggs1, for someone like you who definitely knows what you are doing, this advice works out well. However, I'm not sure it will help the OP who is struggling with getting sharp pictures and we suspect that he's having problems with too slow a shutter speed.  Using Av and with a fixed ISO...if the ISO is too low for the required light (the OP may not know to increase it as needed) then he will be no better off than in P mode...his shutter speed may be set too slow with blurry pictures.  

In most of my BIF situation, my Auto ISO varies from 100 all the way to 2000...setting ISO at 400 as you suggested would have landed half of my shots in the blurry category due to lack of shutter speed....