AI Focus & AI Servo capabilities

[Scottes]

Say I was standing still with my 20D in AI Servo and something was coming directly at me. Some large enough and distinct enough so that the camera had no problems autofocusing.

How fast could that thing be traveling before the camera would have a difficult time predicting and focusing on that subject?


Now, considering the same shot in AI Focus. How long would it be before the camera kicked over to AI Servo?

[CyberDyneSystems]

Assuming the Camera detects the motion of the subject with AI Focus.. then the tracking speed should be identical from AI servo to AI focus.

All AI Focus is.. is allowing the camera to automatically switch between Single shot, and AI servo. So in your instance.. in a perfect world AI Focus would detect the motion and switch to AI servo mode and start tracking.. the tracking results would thenm be identical all it is the same system entirely.

The trouble is ,. I have found that the camera's Idea of when to switch from Single to Servo or vice versa is totally inconsistent.. the only consistency I have seen is that it consistantly does the opposite of what I want it to do.. thus I never use AI focus anymore.

As to actual speeds.. I have no idea... but again.. IF AI focus works the way it should.. then the two speeds should be the same. I'd say your chances though in real life are 50-50% that AI focus will even start to track, as opposed to remeining in single shot.

[Scottes]

So if the camera won't kick from AI Focus to AI Servo then it must not detect enough motion, right?

So who's to say that AI Servo will even work?

If it can't detect enough motion to switch modes then how can it detect enough motion to predict the proper focus point??

[CyberDyneSystems]

My experience has been that it simply has more trouble switching to servo from single shot automitically than it has actually tracking when it doesn't need to make the decision to track... When your allready in AI Servo.. the camera KNOWS to track.. period. It doesn't have an option.

You know.. the "real man's" cameras don't even offer AI focus... :wink:

[Scottes]

....and it doesn't have AF either. Or a lens even. A real man's camera is just a big rock. It's a B&W model and just comes with a chisel.

[CyberDyneSystems]

lol,.. I was referring to the 1D... but point taken! :)

[drisley]

Argh! I HATED AI AutoFocus on the Rebel. :evil:
That was the main reason I got the modded firmware (notice I didnt use the "H" word).
Even thought the Servo needed a quick trigger finger to work, it was preferable to the inconsistent AI Autofocus. :roll:

[Scottes]

OK, OK, I'll switch to AI Servo... Sheesh. :D


But are you supposed to constantly hear the focus motor whirring with AI Servo when * is engaged? That just didn't sound right to me, and it makes me nervous.


Note: The good thing about the old Rock & Chisel camera was that film was free and available everywhere. It had an aperture of f/1, but the fastest shutter was 1/30 of a month.

[drisley]

Use AI Servo when you need to, and One Shot when you need to.
AI Autofocus is just not reliable IMHO

[PacAce]

The answer to your question, little Grass Hopper, lies within. Within the lens, that is. How fast a moving object has to be moving and still be trackable by the camera depends on the AF mechanism of the lens. Newer lenses, such as the 70-200 f/2.8 IS L can keep up with an approaching object a lot better than the old 100-400 IS can.

And, as far as AI Servo is concerned, as you noticed, the AI Servo is ALWAYS checking the focus and adjusting it accordingly, sometime to the point of being very annoying, as long as the shutter button is depressed, half-way or fully.

[PacAce]

Note: The good thing about the old Rock & Chisel camera was that film was free and available everywhere. It had an aperture of f/1, but the fastest shutter was 1/30 of a month.

Well, all that changed in the Flintstone Age when Rockpeckerus Pterodactylus came into existence. Pictures then took only 1/30 of a minute to capture.

[Cadwell]

Note: The good thing about the old Rock & Chisel camera was that film was free and available everywhere. It had an aperture of f/1, but the fastest shutter was 1/30 of a month.

Mmm... sounds ideal for shooting motor bike racing. The damn things corner so slowly that last time I tried shooting them I was panning about 30ft ahead. :lol:

[CyberDyneSystems]

Yep.. the AI servo will be "whirring" as long as the focus button is engaged... be it a half shutter button press,.. or the * button.

But this is half the point of switching CF#4 to focus usig the * button.. doing so puts that control at your finger tips... and take it away from the camera.

It takes a while to get used to... but in the end it is total control.. The Camera is ALLWAYS looking for better focus as long as YOU tell it to by pressing the *.

If the motor running bugs you.. stop pressing the star... :wink:

[Cadwell]

:shock: I am being censored!

I want to make it plain to the world and his dog that I have never used the word "darn" in my entire life. It does not form part of my vocabularly. In fact the only context I would even consider the word is in relation to socks!

The board's software is substituting "darn" for what I really typed! :shock:

[CyberDyneSystems]

IT WASN"T ME!!!!!!!!!

damn damn damn

[CyberDyneSystems]

Hah.. now I'M being censored!

Damnit all!

[Cadwell]

IT WASN"T ME!!!!!!!!!

darn darn darn

Nah... it's a damn auto-substitution by the looks of it!

[Scottes]

I ran into that the other day. Luckily I previewd that long-winded lens review, and noticed the lowercase "darn" at the beginning of the sentence.

CDS won't ever get censored though, because the system isn't smart enough to catch his spelling. :D

[CyberDyneSystems]

Spelling?.. what spelling?.. it's secret code!

[nosquare2003]

Use AI Servo when you need to, and One Shot when you need to.
AI Autofocus is just not reliable IMHO

I prefer "One Shot" over "AI focus" any time -- even for moving subjects. It's too bad for no selection.

(In fact, I do not always use AI Servo for moving subjects...)

[stevekwiz]

Suppose I want to take pictures of my granddaughter on a swing. I'm standing 3 feet from her at the closest, and 12 feet when she's furthest away. Can the 20D track this and deliver good pictures? How about the older 1D? Answer could determine which one I buy.

[CyberDyneSystems]

Really.. they both could.. the 1D will definately do it better/more consistently.

[robertwgross]

If the swinging granddaughter problem can't be solved any other elegant way, then you can always set a fixed focus on a pole or something at one end of the swing arc. Then when she swings into it, you snap.

---Bob Gross---

[Cadwell]

If the swinging granddaughter problem can't be solved any other elegant way, then you can always set a fixed focus on a pole or something at one end of the swing arc. Then when she swings into it, you snap.

---Bob Gross---

:shock: That's a very cruel thing to do to his granddaughter! :shock:

[robertwgross]

I suppose that "swinging granddaughter" has another connotation, also.

---Bob Gross---

[kawter2]

isn't the the 300d full time AI autofocus?

[robertdrake]

This is dumb questions, but I have to ask it. Why doesn't the red AF points show up when in AI modes?

[Cadwell]

I suppose that "swinging granddaughter" has another connotation, also.

---Bob Gross---

I suppose it does, but let's not pursue that one :lol:

[Ferdinand]

Using CF to set AF to * I have AI Servo on 100% of the time :D me lazy.

[robertdrake]

Let me try this again. When I'm using AI Servo, the lens does this dance, jumping in and out (even if focused on the ground) and none of the AF points lights up. This "normal" behaviour"? It would makes sense if it is, I just didn't expect it.

[Scottes]

Let me try this again. When I'm using AI Servo, the lens does this dance, jumping in and out (even if focused on the ground) and none of the AF points lights up. This "normal" behaviour"? It would makes sense if it is, I just didn't expect it.

Yes, it's normal behavior. I have no idea why exactly, but this certainly occurs to several of us.

[CyberDyneSystems]

Yep.. it's normal.

[ne14golf]

Just wondering, if there are any pros or friends of pros...what setting do you use?

Also when looking at the MkII, I noticed only an AI Servo setting and no AI Focus setting. I'm assuming that the AI Focus setting is not very reliable and not needed, just set on AI Servo and shoot.

Thanks,
Tyler

[CyberDyneSystems]

The Sports Pros (Sports Illustrated) set CF # 4 to to 1 and leave the camera in AI servo. (again.. on the Pro bodies "AI Focus" is not even availble.. so even Canon knows it's "bunk"

[robertdrake]

You're standing on the road, bicyclists are coming straight toward you, which focusing mode do you use? I would think the easilist and most effective would be manual fcousing.

[Cadwell]

You're standing on the road, bicyclists are coming straight toward you, which focusing mode do you use? I would think the easilist and most effective would be manual fcousing.

I'm standing at the race track, the cars are coming right at me at a rapid rate and I use AIServo. It works very well.

[ccp900]

id much rather you get out of the way....oh and im a thread necromancer hehehehe....

but why do you need to CF the * to focus if youre in AI servo?

[door]

Regarding the AF light in AI servo and AI focus: could it be that in these modes the camera defaults to using all AF points in order to track the moving subject better, regardless of whether a specific AF point has been chosen?

If my hypothesis is complete hogwash, then in theory, would it be better to keep all AF points active when tracking a moving subject? I normally keep just the centre AF point active.

[Curtis N]

Door,

Take a look at this post by JRSForums (http://photography-on-the.net/forum/showpost.php?p=2122799&postcount=391)in another thread for a good explanation.

[jrsforums]

Regarding the AF light in AI servo and AI focus: could it be that in these modes the camera defaults to using all AF points in order to track the moving subject better, regardless of whether a specific AF point has been chosen?

If my hypothesis is complete hogwash, then in theory, would it be better to keep all AF points active when tracking a moving subject? I normally keep just the centre AF point active.

I suspect the reason Canon does not flash the focal points used is twofold.

First, if in all points, flashing the point initially used is meaning less as it may change in the next instance as the moving object is being tracked and another point may pick up the object. If a specific focal point set, the point will flash when AF is initiated, which I suspect is just to remind the shooter which is being used.

Second, it would be rather annoying if the AF point(s) flashed each time the image was sampled (the rate varies based on light level...faster at higher levels).

One add'l piece of info, while in Servo mode you will know that the object continues to be tracked (in focus) if the light in lower right is off. If it flashes, focus/tracking has been lost.

[door]

Door,

Take a look at this post by JRSForums (http://photography-on-the.net/forum/showpost.php?p=2122799&postcount=391)in another thread for a good explanation.

Thanks for that link. Assuming that the info in that thread is accurate, it answers my questions perfectly.

Based on that info, it appears to me that the best setup would be CF4-1, AI servo and AFPS.

With this setup you effectively don't need to change anything to get:
1. One shot (just press * then release)
2. AI servo (press and hold *)
3. Centre focus point selector only in "one shot mode"
4. All focus points active once tracking a moving subject

This gives best of all worlds, except when taking a snapshot of a stationary subject where focus point and point of exposure metering are the same. In this situation you still have to press 2 buttons (* and shutter) whereas in CF4-0 you would only have to press the shutter button (albeit halfway then fully).

Presumably for these snapshots you could simply select the green square (I've ducked already!).

Oops I've just thought of something else - what happens in P mode?

[door]

Oh and one more thing. The switch from centre focus point to all points when tracking - does this also happen in AI focus mode? Also will initial focus still be done with the centre focus point even if AFPS is selected?

[jrsforums]

Oh and one more thing. The switch from centre focus point to all points when tracking - does this also happen in AI focus mode? Also will initial focus still be done with the centre focus point even if AFPS is selected?

Stay away from AI Focus. It will cause you too many unknowns and delays. You should know if your object is moving or not. (BTW...if AI Focus chooses one-step, AFPS will initialize on any point....closest "subject(s) to camera under FPs).

If you are in AFPS with Servo, just remember that the center point will acquire focus first, which may require focus/recompose...which is OK if the object is not too close (change of focal plan with recompose)....and if you release the '*'(pseudo one-step), otherwise it will "track" and focus will change.

Good detail on all the modes, written up by Doug Kerr, is at http://doug.kerr.home.att.net/pumpkin/20D_CF04_chart.pdf