AI servo - what's the downside

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sheridant

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playing with a 85mm 1.2 lens - is it madness not to ised ai servo given the shot depth of field - is there a negative to using it other than bettery life

and why shen using it does the red focus light come back up to confirm focus on a 5d MKii


Thanks
 
It's not madness but may not be the ideal solution. Are you tracking movement or simply trying to cover for slight subject movement (or your own movement)?

There will be a certain amount of prediction built into the AI servo algorithm and "swaying" is not thing it's neccessarily trying to cover as it's more likely attempting to plot and then predict the next ideal focus distance.

One little extra worthy of mention.....
If you're working fairly close (portraiture type distances) then I think you would be advised to switch off the expanded AF points when using the 85L. There's a very real chance that one of the peripheral zones will be acted upon and this can be a hindrance when DoF is so shallow....(CF:17 set to 0 would disable them).

HTH

Bob
 
On the 5D servo mode only tracks something coming towards the camera. Try it with stationary subjects - you will find it consistently front-focuses, presumably as a result.
 
slight subject movement not my own is the reason for using it - the other downside i see is that you can't hold the shutter button down - focus they recompose - but is that it?
 
I use servo while out shooting birds (feathered) with my 50D.

This is for static type shots of bird on perch. Why? Simple, the bird moves about, a couple of inches here and there, I can follow the bird knowing that the camera will refocus for me.

I have to be very careful where I leave the AF point because one slip and the birds eye moves out of focus. Now at F4, 300mm and a fairly close range the DOF is incredibly small - not sure how it compares to the 85mm but still, the theory is good IMO (As long as you have a real steady hand and can keep the af point where you want it).
 
malla1962 said:
Forget focus recompose.
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don't worry - guessed that before i even put the lens on - BTW mall - thanks for getting the 85mm 1.2 lens to me - absolutely love it - it's like a classic car - pain to live with - but oh so worth it
 
sheridant said:
don't worry - guessed that before i even put the lens on - BTW mall - thanks for getting the 85mm 1.2 lens to me - absolutely love it - it's like a classic car - pain to live with - but oh so worth it
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No problem mate, hope you get more use out of it than I did, never really used it much but you can see that by the condition.:D
 
pearce_jj said:
On the 5D servo mode only tracks something coming towards the camera. Try it with stationary subjects - you will find it consistently front-focuses, presumably as a result.
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I can't dispute what you're saying James as I don't have a 5D to try it on. However, AI Servo will not "re-focus" until movement is detected and hence a stable camera and a stationary subject would result in focus being achieved in exactly the same manner as "one shot" AF...ie, there are no commands to the lens to change position.

Bob
 
pearce_jj said:
On the 5D servo mode only tracks something coming towards the camera. Try it with stationary subjects - you will find it consistently front-focuses, presumably as a result.
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pearce_jj said:
What I wrote above is per my own actual experience with the 5D, and what Canon actually told me, since I returned the body because of it when it was new.
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So what you should have said is - "On my 5D..." What you've written implies that every 5D suffers from front-focussing when used in AI Servo on static subjects. That is not true.
 
Isn't it? Canon said otherwise and I'd be interested to know for one.
 
pearce_jj said:
Isn't it? Canon said otherwise and I'd be interested to know for one.
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What, Canon have released an official statement that all 5Ds front-focus in AI Servo? Or is it perhaps that some pimply-faced youth in Dixons said this?

I'm sure that if Canon had said that all 5Ds suffer from this problem we'd have heard a lot more about it - like about 5000 posts in various fora complaining bitterly.

What, exactly, did 'Canon' (or the PFY, or somebody reading a script in a call centre in Delhi) say? Was it "Oh, yes, that's a well-known problem in one of out biggest-selling cameras. They're crap really, don't know why anybody buys one." Or was it "Hmmm, it sounds as if your lens may be front-focussing on your camera. It might be a good idea to send them in for calibration."
 
hollis_f said:
What, Canon have released an official statement that all 5Ds front-focus in AI Servo? Or is it perhaps that some pimply-faced youth in Dixons said this?
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I'm sure James is wise enough not to accept the word of a "PFY" in a retail outlet.

James is certainly not alone in having the symptoms he describes. The very same results are being seen by Philthejugler and (coincidentally) were being discussed elsewhere yesterday.....Phil is also experienced enough to make an accurate assessment of what is happening with his shots.

Bob
 
PFY - lol!

It's simple enough to test. Tripod, fast lens (won't see it so much at F4), classic angled test chart thingie, centre spot, shoot samples between the modes.

Servo will front focus because, I was told by a service centre contact who's details were in the box when camera was returned (and over the phone yes) that the camera assumes that the subject is travelling towards the camera and hence always compensates for this. Certainly having it calibrated in the returns process made no difference whatsoever.

NB 5D Mk.I I'm talking about here.

Canon Bob - interesting someone else has noted this, thanks for that.
 
still don't understand whether AI servo is a better option for taking portraits when using large apertures on a 5d MKII - but I think judging from the answers probably yes?

though I'm guessing - it's probably worth using one shot when I'm using the focus points other than centre

Thanks veryone for input - and sorry for starting a fight :)
 
sheridant said:
still don't understand whether AI servo is a better option for taking portraits when using large apertures on a 5d MKII - but I think judging from the answers probably yes?
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I assume that you're not firing off a burst? The first shot in AI servo will be shutter priority and may negate your intentions....subsequent shots (if in burst mode) would be focus priority but prediction would be erratic at best.

sheridant said:
Thanks veryone for input - and sorry for starting a fight :)
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Not a fight, just healthy discussion.

Bob
 
Canon Bob said:
I assume that you're not firing off a burst? The first shot in AI servo will be shutter priority and may negate your intentions....subsequent shots (if in burst mode) would be focus priority but prediction would be erratic at best.

Bob
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Don't quite unerstand - If I'm shooting in Av using AI servo - the first shot will be in shutter priority not aperture priority - that doesn't sound right
 
sheridant said:
Don't quite unerstand - If I'm shooting in Av using AI servo - the first shot will be in shutter priority not aperture priority - that doesn't sound right
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Sorry, poor terminology on my part.

Shutter release priority...ie, when you press the shutter button.

Bob
 
so if i understand - in burst - the first shot will be when you press the shutter release, the following when focus is re-established?
 
sheridant said:
so if i understand - in burst - the first shot will be when you press the shutter release, the following when focus is re-established?
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Yes, that's about it. This is an extract from a Canon document on the subject

Specifically, in a continuous AI Servo AF sequence, the first exposure is always handled as ‘release priority,’ while subsequent exposures in that sequence are handled with ‘focus priority’ according to Canon’s definition of that term.

Bob
 
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