When are you using AI Servo or AI Focus?

[MohaimenK]

I've always shot in one shot but is there a great advantage to shooting in AI Servo or AI Focus? Say during moving subjects? Or do typically 1 shot takes care of it?

Here's an example of a shot I took. I pretty much missed focus because it was a sudden shot. But would it have been better having it on Ai Servo?

 

[Overread35]

Some will say one shot is enough -others that AI servo should always be used - and then again some will insist on manually focusing -and that's all just in bird photography!

AI focus is often avoided however because its a predictive mode -instead of always being a oneshot AF or a continuous AF the camera tries to decide for you as to which you need (ie it tries to decide if its looking at a shifting or static subject). And as thus tends to get it wrong or give a slow reaction time.

Generally I site all the time in AI servo because most of what I shoot is moving - but I've never had a problem with AI servo shooting a static scene either. Some use oneshot and recompose - I use AIservo and recompose by using the backbutton af - so that I don't activate AF with the shutter button (so you use the backbutton to focus - then just don't press it whilst recomposing)

 

[MohaimenK]

Thanks Ovveread. So if I had used Ai Servo for that shot, would it have been easier for me to capture that person with sharper focus? Or it doesn't matter if I miss focus to begin with.

 

[Overread35]

AI servo keeps the AF running the whole while so it will recalculate the focus if it detects that the subject is moving out of focus - this is one area however where the camera body itself comes into play -a rebel series body won't (with the same lens) track motion as well as a 1DMIV or 7D. The lens you use also has an effect - those with faster AF will do better in such cases as those with a slower AF motor

 

[Big Mike]

One thing to keep in mind, is that the AF assist light (say on a 430Ex or 580EX) only works when the AF is in single shot mode.

I used to use AI focus most of the time, but then was puzzled when I had such a hard time focusing in very low light. Now I use one shot when the AF assist light would be handy...and if I remember, I switch it to AI Focus for action type shots.

 

[MohaimenK]

The sad thing was that shot was taken with a 5d MK2 with 70-200 2.8 II :thumbdown:
I guess, since I missed focus that was the initial issue. So I guess I have to lock focus initially before AI Servro can start to think on its own?


One thing though, I was a bit close to the subject.

This was better on the other hand. I was further away.

 

[MohaimenK]

One thing to keep in mind, is that the AF assist light (say on a 430Ex or 580EX) only works when the AF is in single shot mode.

I used to use AI focus most of the time, but then was puzzled when I had such a hard time focusing in very low light. Now I use one shot when the AF assist light would be handy...and if I remember, I switch it to AI Focus for action type shots.

Yeah, from what I read, the AI focus is supposed to work for both. If the subject is still it'll take the shot at one shot but if the subject starts to move then it changes itself to AI Servo mode.

 

[memento]

One thing to keep in mind, is that the AF assist light (say on a 430Ex or 580EX) only works when the AF is in single shot mode.

I used to use AI focus most of the time, but then was puzzled when I had such a hard time focusing in very low light. Now I use one shot when the AF assist light would be handy...and if I remember, I switch it to AI Focus for action type shots.

son of a *****!

i'm pissed at Mo for not starting this thread 2 weeks ago.
i TOTALLY blew a bunch of reception pics at my sisters wedding.
and THIS ^ is exactly why.

thanks Mike. i learned something today!

 

[MohaimenK]

^^^^ LOL!! You missed focusing or you overexposed the pix with too much flash?

 

[memento]

totally unfocused.
i was really bumded too. there were a lot of family members from all over the country. i blew a great one of my kid with her great grandma.

i thought i was drunk

 

[MohaimenK]

totally unfocused.
i was really bumded too. there were a lot of family members from all over the country. i blew a great one of my kid with her great grandma.

i thought i was drunk

Ohh man sux! Yeah so far I haven't been in a situation to use the beam. But at least it was your sister's wedding and not a paid one

 

[Big Mike]

So I guess I have to lock focus initially before AI Servro can start to think on its own?

No. In the AI modes, focus won't lock...it just constantly tries to focus while you have it activated.

That's one reason why I don't have AF activated by my shutter release button. I have my * button (thumb position) set to activate AF. That way I can activate AF by pressing it and lock it by releasing it. The newer models have an AF-ON button added beside the * button.

 

[Overread35]

Ahh yes I always forget about the focus assist light and how it won't work in AIservo mode! Made me all manner of confused first time I used it as well and couldn't get the flash to help focusing.

The sad thing was that shot was taken with a 5d MK2 with 70-200 2.8 II :thumbdown:
I guess, since I missed focus that was the initial issue. So I guess I have to lock focus initially before AI Servro can start to think on its own?

The 5DM2 does not have an outstanding AF system (the 7D beats it by miles in this department) but it should still be very usable (I know several wildlife shooters who use a 5DM2 in the field and even the older 5D).

Also yes you are right you have to lock the focus first otherwise the camera hasn't got a lock on anything to work with.

 

[ababysean]

So on the NikonD90 does anyone know how to get it off AF-A? I know on my D3000 I could choose between AF-A/AF-C/AF-S but I can't seem to find the choice on the D90

 

[kundalini]

This is undoubtedly a Canon speak thread.

ababysean....... run away.



But on the other hand, I'm not sure about the D90, but it seems to me that the options are (using the D700 as a guide) you have three choices. AF-S, AF-C and Manual. I'm not sure what AF-A is. AF-S is single focus, meaning hit your focal point and you're done. AF-C is continuous, meaning it tracks moving subjects and Manual.... duh. Please enlighten me on AF-A.