AF tracking speed

[Roger Clark]

I did a little experiment with tracking speeds. I took a canon 300 mm f/2.8 L IS lens with canon 2x TC. I manually moved the focus to minimum distance, and then pointed at a bright distant source (the Moon in a dark sky), I half pressed the focus and counted how long to come into focus. Here are some results:

1D Mark II: 4 to 5 seconds
5D Mark II: 4 to 5 seconds
7D: 4 to 5 seconds
1D Mark IV: 2 to 2.5 seconds.

Then 300 f/2.8 with no TCs:

1D Mark IV: about 2/3 second or a little less.

Also, as expected, changing "tracking speed" in the custom functions do not change the time to achieve initial focus.

Roger

[Jackie Schuknecht]

Interesting Roger, will consider this when I set up my 7D. i.e. tracking speed

[Roy Churchill]

Interesting test Roger. When I use the 300/2.8 with a 2x I like to use a focus limiter (usually 6.4mts > infinity) I have not timed the focus but it seems a lot quicker when limiting the focus range.

[Axel Hildebrandt]

Thanks for posting the results, Roger! I'm a bit surprised that the 1D4 is so much faster at acquiring focus.

[Roger Clark]

Interesting test Roger. When I use the 300/2.8 with a 2x I like to use a focus limiter (usually 6.4mts > infinity) I have not timed the focus but it seems a lot quicker when limiting the focus range.

Roy,
I agree: limiting the focus rang helps time from that limit compared to minimum focus point. In practice one would never/vary rarely encounter such a situation, so the total time is probably not that relevant to real world imaging. But it does illustrate the relative speeds. I was surprised that over the generations of cameras, the times were so similar, until the 1D4.

Roger

[Roger Clark]

Thanks for posting the results, Roger! I'm a bit surprised that the 1D4 is so much faster at acquiring focus.

Axel,
Me too. I actually did not set out to do this test. I was comparing my 300 f/2.8 and 500 f/4 image quality with various TCs and bodies when I noticed how much faster the 1D4 focused.

Roger

[Ian McHenry]

Thanks Roger
Looks like a strong case to leave TC off camera when taking pictures from an aeroplane.
Cheers: Ian Mc

[Colin Knight]

Roger, I believe with different subjects you'll get quite different results- I was trying to determine the correct setting for AF tracking speed for birds taking off. The bottom line is that focus locked much more quickly when set to fast. More specifically, I got 5 for 5 frames in focus on a duck taking off with AF tracking sensitivity set to fast. With a goose taking off, I got 2 out of 5 in focus (and it was noticeably slower to achieve focus in addition to a goose being a slower bird) with tracking sensitivity set to slow. My theory is that the AF sees a "different" subject when a sitting bird transitions to a flying bird. The flying bird is "interference" and AF is slow to lock on the "new" subject. However, with tracking sensitivity set to fast, the camera immediately locks on to the "new" subject- the bird in flight. This doesn't apply when activating AF on a bird already in flight, only when tracking a bird transitioning from sitting to flying, trying to catch that perfect takeoff moment. I would like to hear others' experience with this as well.

Thanks for the thread and posting your resuts Roger.

[Roger Clark]

Colin,

As explained by Doug Brown here on BPN and in Canon documents, the tracking sensitivity does not change the speed of acquisition. When you half press the shutter button, the speed the camera moves the lens to best focus and the speed will not change with different tracking sensitivities. The tracking sensitivity has to do with the length of time when you are tracking a subject and move to a different subject: there is a delay before the camera will act to change focus. Tracking sensitivity changes that delay time.

So if you are sitting with an AF point on a sitting bird, waiting for it to take off, then I can see the tracking sensitivity would be a factor, as if set to slow, the camera will delay longer before changing the focus. Doug makes an argument that when tracking birds in flight (that is not your case) that if you slip off the bird, you may have enough time to get back on the bird before the camera starts to lock onto something else. There is great merit in that strategy.

But in your case, the transition from slow to fast with your finger already pressing on the shutter, the camera needs to act fast, so setting tracking sensitivity to fast would be the way to got. Alternatively, you could keep your finger off the shutter, and when the bird starts to take off, half press the shutter and the focus acquisition would be equally fast whether tracking sensitivity was set to slow ot fast. Then the question is, which reacts faster: the camera or you? If you have faster reaction, then setting tracking sensitivity to slow and keeping from pressing down on the shutter until you want to focus may be the way to go.

I have been trying to perfect these methods (fast versus slow tracking speeds. I've been photographing cliff swallows (extremely fast) and find that I do get a higher keeper rate with tracking sensitivity set to fast. This is because the birds dart back and forth in random patterns, forcing the camera to change focus from a given projected trend. If tracking is slow, the camera (1D4) can't keep up with the birds (I'm not helping much); with a 500 f/4 I can only keep them in the viewfinder for a few seconds.

Doug, I hope you are reading and will comment.

Roger

[Colin Knight]

Thanks Roger! Looking forward to more input as this thread goes on.

[Jim Neiger]

Roger,

Are you perhaps getting Doug Brown and I mixed up? I'm the one who has commented on tracking bif and the tracking sensitivity function etc. quite a bit recently.

The TS function works best on SLOW when used in conjunction with the bump focus technique to override the delay. If the bump focus technique is not used, then the best setting depends on the situation and circumstances. Since you can't change it quickly on the fly, it will help you sometimes and hinder you sometimes. You can improve your success rate by combining SLOW with the bump technique.

[Jackie Schuknecht]

WHAT is BUMP FOCUS?????

[Jim Neiger]

WHAT is BUMP FOCUS?????

See this thread: http://www.birdphotographers.net/forums/showthread.php?1949-Bumping-the-focus-for-BIF&highlight=bumping+foucs+bif

[Jackie Schuknecht]

Thank You!

[Roger Clark]

Roger,

Are you perhaps getting Doug Brown and I mixed up? I'm the one who has commented on tracking bif and the tracking sensitivity function etc. quite a bit recently.


Jim,
Oops! Yes, my mistake. Thanks for correcting me.

Roger

[Sidharth Kodikal]

Axel,
Me too. I actually did not set out to do this test. I was comparing my 300 f/2.8 and 500 f/4 image quality with various TCs and bodies when I noticed how much faster the 1D4 focused.

Roger

Hi Roger, if I may ask, what were your findings on the IQ comparison? I currently use a 300 2.8 with a 2x and am tempted to get a 500 f4. However I really like the portability that the 300 gives me, but might change to a 500 more readily if the IQ difference makes it worth it.
Thank you.

[Roger Clark]

Hi Roger, if I may ask, what were your findings on the IQ comparison? I currently use a 300 2.8 with a 2x and am tempted to get a 500 f4. However I really like the portability that the 300 gives me, but might change to a 500 more readily if the IQ difference makes it worth it.
Thank you.

Some of my results are here:
http://www.clarkvision.com/articles/telephoto_reach/

I was partly doing the testing to see if I would be satisfied with taking a 300 f/2.8 on my next Tanzanian safari instead of a 500. I'm taking the 300. It will give me the image quality and reach that I desire and it is lighter so I can react faster. I want to be able to quickly deploy the lens, and move the lens from the top of the vehicle to a window, to the floor with the side door open. I can do that with the 500 but it is so much heavier that I can't do it as fast as I want. And I will do some hiking, and taking the 300 is easier on the hikes.

I am particularly intrigued at how well the 300 f2/8 works with stacked 2x + 1.4x TCs on a 1D4.

Roger