Lens Focus Question

[Canonowner]

Hello

I'm new to this forum and have a question about an issue that I have time to time with my camera and lens I use for bird in flight photography.

Bird in flight photography is a new hobby for me since the Spring of this year and I use the Canon 100-400 version 2 lens on a Canon 40D body.

I have noticed a few times that when I completely lose focus on the bird while tracking it in the open sky with no obstructions, I have a hard time trying to get the camera /  lens to properly focus on the bird again.

I'm at the 400mm end of the focual length when this happens.

I can understand the camera and  lens having a hard time trying to refocus on a small object in the sky so, what I do is point the camera towards something on the ground like a tree or a building to try to bring things back into focus.

What I have noticed when doing this is, it takes many attempts to get the camera / lens to reacquire focus on the tree or building before I can even attempt to try and get focus on the bird again.

I'm still at the 400 end of focual range when doing this.

I have tried a couple of times to manually refocus the lens on the bird but, I have a hard time trying to find the bird again and I'm just not good at using this method at this point.

So my concern is, is this a normal issue for a situation like I've described, and if it isn't, what might possibly be the cause?

My thought is that maybe it's the AF system of the 40D.

The body is 9 years old and since BIF photography is new to me, I have no past experience that I can relate to for this kind of situation.

There are no AF issues at all with still objects.

I'm hoping that there are no issues with the lens.

I bought it brand new Sept. of last year.

If anyone has a possible explaination for why this happens, or how to prevent this from happening, it would be appreciated.

If this is of any help, my BIF settings are:

Back button focus.

AI servo mode.

High speed continuous shooting.

All focus points are active as I'm normally tracking the bird in open sky.

The lens focus range is set to 3m to infinity as the birds are always more than 3m away from me.

[Waddizzle]

“Unfortunately, my time for BIF photography is very limited for the most part.

So, I use all AF points being active to increase my chances of getting some in focus shots.

I only use all AF points when the bird is an open sky setting..usually a clear blue sky.. with nothing to pull focus off the bird.

If the bird is flying among trees or buildings, then I use the centre AF point only, with little success.

I know I would have zero chance of getting a flying small bird in focus just using the centre AF point.“

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I get the best results enabling all AF points when trying to focus on a BIF with a busy background.

When you use just a single AF point, the camera will focus with just that AF point.  If your aim drifts off target, then so does your focus.  When you enable all AF points, the camera will try to focus on what it determines is the nearest object to the camera.  

More times than not, when you photograph a BIF against a busy background, the BIF is typically the closest subject to the camera.  As a result, the camera will tend to track [ using AI SERVO mode, of course] the closest subject, which is the BIF.  In fact, this is true for the majority of BIF shooting scenarios.

[Canonowner]

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@Waddizzle wrote:

“Unfortunately, my time for BIF photography is very limited for the most part.

So, I use all AF points being active to increase my chances of getting some in focus shots.

I only use all AF points when the bird is an open sky setting..usually a clear blue sky.. with nothing to pull focus off the bird.

If the bird is flying among trees or buildings, then I use the centre AF point only, with little success.

I know I would have zero chance of getting a flying small bird in focus just using the centre AF point.“

—————————————————————————————————————

I get the best results enabling all AF points when trying to focus on a BIF with a busy background.

When you use just a single AF point, the camera will focus with just that AF point.  If your aim drifts off target, then so does your focus.  When you enable all AF points, the camera will try to focus on what it determines is the nearest object to the camera.  

More times than not, when you photograph a BIF against a busy background, the BIF is typically the closest subject to the camera.  As a result, the camera will tend to track [ using AI SERVO mode, of course] the closest subject, which is the BIF.  In fact, this is true for the majority of BIF shooting scenarios.

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That's interesting that your method is to use all AF points for BIF photography with a busy background.

I'm not saying that it's the right or wrong method but any instructional videos for BIF photography I've watched, suggest that a busy background is when you do want to use the centre AF point only.

I understand your explanation for using all the AF points.

Personally, I like using all AF points being active in open sky situation.

When using only the centre AF point, I find it hard to keep it on the moving subject.

Especially on the small target of the head when the bird is far away.

Although, I have been out the past few days practising using only the centre AF point and I'm starting to get more shots with the AF point on some part of the bird at least, even a few directly on the head.

So far with most of my BIF photography, I haven't had to contend with a busy background but, I will try using all AF point being active next time that situation presents itself, and see what kind of results I get.

[Waddizzle]

"That's interesting that your method is to use all AF points for BIF photography with a busy background.

I'm not saying that it's the right or wrong method but any instructional videos for BIF photography I've watched, suggest that a busy background is when you do want to use the centre AF point only.

I understand your explanation for using all the AF points."

I do change up, depending upon the relative distances between the subject and background.  When the background is close to, or within, the DOF I will use just the center zone of AF points.  Or, just the center with four AF assist points.

However, the shot that I posted was with all AF points active.  The AF system can easily track the BIF when the background is outside of the DOF.  The real trick is getting the initial focus lock.