FAST action autofocus

[Hal Everett]

I don't know whether to post this here or in general photography questions. It is not an image I am proud of, but one I have repeatedly failed to get.

In the Samish Flats, WA there is a regular winter spectacle of Peregrines hunting a large flock of Dunlin next to the road. They are on, and otherwise surrounded by private property. If you wait several hours it is possible to see this once or twice. Maybe one in 15 days are bright enough to shoot it, and I can only shoot weekends, so opportunities are limited. The falcons come from behind at incredible speed in a low pass. Thousands of Dunlin fly up from the mud, and the falcon usually gets one within 10 seconds, then flies off. Frequently, the falcon is concealed by the Dunlin, but once in a while a shot is possible.

I am usually able to keep the falcon in the frame, but have never gotten focus on the falcon, no matter what the autofocus settings. It always ends up focusing on the Dunlin.

I am using a 7D with an 800mm f5.6 lens on a Wimberly tripod. This shot was taken at 1/1600 second (it was not light enough for 1/2500 at acceptable ISO), f6.3, ISO 800, EC+1 1/3, AI servo with autofocus point expansion. The results are the same with zone autofocus. My only idea at this point is to try a shorter lens, or consider a 1D series. Any suggestions are appreciated, but they are probably too late for this season.

Hal

[arash_hazeghi]

Hi Hal,
I guess the appropriate forum is Eager To Learn, moderator can move the thread over there.
As far as 7D AF is concerned, definitely do not try zone or expansion mode for this scenario, the moving Dunlins will shift the focus to BG in this case, like little contrast target! Your best bet is starting to track the Peregrine before it enters the busy BG scene, or if possible get within 70 ft (20m) of the falcon and use the focus limiter on the lens to set max focus range so that the camera cannot shift to BG. once the falcon is flying against the busy BG it is very difficult if not impossible to get the 7D to acquire focus on it, because 1) it is flying erratically and fast 2) it has the same color and contrast as BG, I have found that 7D AF system is not very good when raptor maneuvers against busy BG.

So the best would be to reposition and start tracking against a plain BG (Sky or distant water for ex), once the falcon enters the busy BG pay close attention to the focus point in the finder, as soon as you see the focus shift to BG bump the shutter button forcing the camera to shift the focus to the falcon. stay with single point only and in this particular case set tracking sensitivity to 0 (normal) and focus priority to main focus priority (as opposed to tracking priority which is usually recommended) this is required for the bumping technique to work. You may also experiment with spot AF mode, it is no recommended by Canon for moving subjects but I have observed it can help it some situations.


Good luck!

[Axel Hildebrandt]

On my camera - I don't have any experience with the 7D - I sometimes change the tracking sensitivity to slow and you could try how it works with the central sensor only.

[Alfred Forns]

Hal I would try the focus sensitivity to slow and bump the shutter until you acquire the focus. I was shooting with Jim Neiger last Sunday and asking him about this setting, tried his suggestion and did very well.

I think the key is getting the sensor on the bird and bump the shutter if its not sharp. After you acquire the bird just keep tracking !! btw it is a tough situation !!!

[Hal Everett]

Thank you all. The falcons come in 3-4 feet off the ground from behind me, so isolating them in the sky is not possible. Frequently the first sign of their arrival is the Dunlins rising from the mud. I don't think I could pivot 180 degrees in just a few seconds and keep the bird in the frame anyway. The bump technique sounds interesting and I will try it. All I can say is that it had better be very fast.

[Jim Neiger]

Hal I would try the focus sensitivity to slow and bump the shutter until you acquire the focus. I was shooting with Jim Neiger last Sunday and asking him about this setting, tried his suggestion and did very well.

I think the key is getting the sensor on the bird and bump the shutter if its not sharp. After you acquire the bird just keep tracking !! btw it is a tough situation !!!

Here is a link to the write up I did on setting the tracking sensitivity and then using it in conjunction with bumping the focus. See # 2 in the post I made. http://www.birdphotographers.net/for...71&postcount=1

[Bruce Enns]

Thank you for posting this Hal, and for the advice offered Arash, Axel, Al and Jim.

Jim, are you using the AF on button on the rear of the camera for your bump the focus technique? There are options on the 7D and 1 series cameras that change when the focusing happens using the AF ON and shutter buttons. What settings do you use for these buttons so that the IS does turn off in between focus bumps? I find that focusing with my thumb feels very strange.

Cheers!
Bruce

[Jim Neiger]

Thank you for posting this Hal, and for the advice offered Arash, Axel, Al and Jim.

Jim, are you using the AF on button on the rear of the camera for your bump the focus technique? There are options on the 7D and 1 series cameras that change when the focusing happens using the AF ON and shutter buttons. What settings do you use for these buttons so that the IS does turn off in between focus bumps? I find that focusing with my thumb feels very strange.

Cheers!
Bruce

I focus with the shutter button. I set the * button to AF lock so I can remain in AI Servo and still shoot still subjects while composing the images in camera.

[Jim Neiger]

Thank you all. The falcons come in 3-4 feet off the ground from behind me, so isolating them in the sky is not possible. Frequently the first sign of their arrival is the Dunlins rising from the mud. I don't think I could pivot 180 degrees in just a few seconds and keep the bird in the frame anyway. The bump technique sounds interesting and I will try it. All I can say is that it had better be very fast.

Pre-focus at the approximate distance that you think you will first photograph the Falcon. Then wait until it comes and focus when it is at about the right distance and you are sure you have the focus point (center only) on the Falcon, then focus and shoot in one motion for a short burst. If you miss, you are likely done, but try letting off the focus, relocate the bird, then focus when you are sure you are on the bird. If the difference in distance when you missed was very far, you may need to pre-focus on the ground at the desired distance and then re-aquire the bird. Practicing your acquisition skills will help you with this. If you are able to put the bird in the viewfinder before you are ready to shoot, see #3 in the thread I linked above and try the technique described there for avoiding the bg by bumping the focus.