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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 08 Nov 2012 (Thursday) 14:25
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Need clarification on AI Servo and BBF

 
jeljohns
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Nov 08, 2012 14:25 |  #1

I love using back button focus, but I think I may be using it wrong in AI Servo.

If I want to use AI Servo with a moving subject, let's say a dog, do I keep my thumb on the * button the entire time I'm shooting frame after frame?

If the dog stops moving, do I release my thumb to lock focus?

I keep getting the moving and non moving situations mixed up and confused. Some clarification would be great!

Also, is AI Servo intended for subjects moving towards and away from you, but not moving left to right?




  
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watt100
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Nov 08, 2012 14:29 |  #2

jeljohns wrote in post #15223013 (external link)
I love using back button focus, but I think I may be using it wrong in AI Servo.

If I want to use AI Servo with a moving subject, let's say a dog, do I keep my thumb on the * button the entire time I'm shooting frame after frame?

If the dog stops moving, do I release my thumb to lock focus?

I keep getting the moving and non moving situations mixed up and confused. Some clarification would be great!

Also, is AI Servo intended for subjects moving towards and away from you, but not moving left to right?

I don't use the back button but when I use AI servo I keep my finger half pressed on the shutter button




  
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JakAHearts
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Nov 08, 2012 14:34 |  #3

As long as youre using the * button for focus, then yes, you hold that the entire time whilst keeping the appropriate focus point on the subject. You use it for all moving subjects, regardless of what direction they are going. If the animal stops, you can either keep the button held down and use the composition you have, or let go and recompose the shot as you see fit.

What camera body are you using?


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Nature ­ Nut
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Nov 08, 2012 14:45 |  #4

AI servo will keep on trying to achieve focus. When I shoot long distance or moving subjects I always use it so in a burst a couple shots will be in great focus. For static shots I will use one shot sometimes so I get the little enjoyable beep. But if you hold AI servo until it stops adjusting you can let go and it is basically one shot focus.

If you stay on target then you can keep the BBF * pressed down in servo mode. however if you wanted to focus on the eye then let go of the * and recompose you can do that too. When I shoot moving wildlife I keep the bbf held down and hit the shutter at the moments I want to grab.

If a subject moves left or right its distance stays the same so focus will remain the same. I still focus with BBF and servo because rarely do things move perfectly left or right for me. If DOF is deep enough it becomes less of an issue to constantly refocus left or right moving things.


Adam - Upstate NY:

  
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jeljohns
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Nov 08, 2012 15:21 as a reply to  @ Nature Nut's post |  #5

Thanks nature nut, jak- I'm shooting with 5DmkII




  
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JakAHearts
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Nov 08, 2012 15:22 |  #6

Then yes, youll need to keep the chosen focus point over the subject while it moves. :D


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jeljohns
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Nov 09, 2012 07:17 |  #7

Ack...so yesterday at the dog park I tried the AI Servo, keeping my thumb on the button the whole time. All my pictures came out soft and not in sharp focus at all. What am I doing wrong? I usually have okay luck with one shot with moving subjects, but I thought AI would work better.




  
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JakAHearts
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Nov 09, 2012 07:35 |  #8

Well, dogs are fast. The 5DII isnt known for its focus abilities. Youll have more luck if the dogs arent running straight toward or away from you. Post up some shots w/ exif settings in tact so we can see. :D

(also, I know it doesnt help, but if you need to take moving shots like this, then you NEED a 5DIII ;))


Shane
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jeljohns
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Nov 09, 2012 07:57 |  #9

I would LOVE a 5diii but couldn't justify the cost. I was working with a 50d and I liked it, but kept butting up against limited ISO in low light. Last month I bought a 5dii used. I'm head over heels for the full frame, but not so jazzed about the focusing. :( there is just no budget for a $3,500 camera right now.




  
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JakAHearts
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Nov 09, 2012 07:58 |  #10

jeljohns wrote in post #15225751 (external link)
I would LOVE a 5diii but couldn't justify the cost. I was working with a 50d and I liked it, but kept butting up against limited ISO in low light. Last month I bought a 5dii used. I'm head over heels for the full frame, but not so jazzed about the focusing. :( there is just no budget for a $3,500 camera right now.

I completely understand. The 5DII is a fantastic camera. Enjoy it! :D What lens are you using when trying to track the animals?


Shane
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jeljohns
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Nov 09, 2012 08:00 |  #11

I currently have a Tamron 24-70 2.8 (use this 95% of the time) and a canon 50mm 1.4




  
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JakAHearts
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Nov 09, 2012 08:11 |  #12

Ah ok. I dont have any first hand use of the tamron, but Ive read its not the fastest focusing lens. So youve got a few things going against you. :(

Sadly, this is one of those situations where better equipment would warrant you better shots. Manual focus perhaps? :D


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Nature ­ Nut
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Nov 09, 2012 08:31 |  #13

If your lens is slower to focus you can try running a smaller aperture so the zone of clarity is bigger leaving a larger margin for error. That will of course depend on the lighting. Using that and a decent shutter speed (1/500 or greater for moving critters) should also help compensate.

Are you using the center AF only?


Adam - Upstate NY:

  
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IslandCrow
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Nov 09, 2012 09:06 |  #14

It's been hinted upon, but in addition to the camera/lens not keeping up with the focus, insufficient shutter speed could be a culprit as well. Depending on what the dog is doing, you may need a very fast shutter speed. For a dog just trotting along, 1/500 or even a little slower should be plenty. If the dog is really moving, you may need something more like 1/1000 to freeze its movement. I own a 5DMII as well, and even though it definitely doesn't have the best autofocus system out there (it really wasn't designed for action) and I tend to switch to my 40D for action shots, I've found that it still seems to do a pretty good job tracking a subject once it's locked on to its focus point. It's generally just in that initial focus where I find it can be slow. It does require a steady hand, though, because once you move off that focus point, it can often be a bit slow to reacquire.

Oh, and good question by Nature Nut. The 5DMII (and most of the other non 1-series cameras) use a simpler algorithm (that's not as accurate) for the outside focus areas. It's usually not a big problem with static subjects, but it can definitely be a bit inconsistent with moving objects.




  
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jeljohns
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Nov 09, 2012 09:50 |  #15

Nature, I am using center focus....but come to think of it a few minutes before going to the park I was fooling around with focus points....I may have left it on all points.

I've never had trouble with my Tamron, so happy with it that I've never felt the need to buy a canon 24-70.

It was around 5:30pm so it was pretty dark, therefore my shutter speed was around 200, a bit too low I guess. I didn't want to push the iso since it was already at 2000.




  
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Need clarification on AI Servo and BBF
FORUMS Photography Talk by Genre General Photography Talk 
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