Equipment Sigma 50mm f/1.4 HSM

No...FTM with lenses with true ring USM can be used in any focus mode...whether its AI Focus or or AI Servo it doesn't matter, at least as long as the shutter is being held 1/2 down. Try it with your 70-200...you'll see.

 

And now I learned that if I set my camera to continuous shot mode with the 50mm (nifty) I might actually get some better "action" portraits in between Or am I completely off here?

 

Continuous Shot mode will not get you better images, it will OTOH allow maximum FPS as long as the shutter button is held down...it has nothing to do with AF. CS is used primarily for action shooting (ex: sports), not so much portraiture.

 

Basically the Canon 50 1.4 is an odd one out, all other micro USM lenses are not FTM, but Canon obviously felt that the 50mm needed it so added a clutch system into the micro USM gearing. Any real USM lens doesn't need the clutch due to the lack of a gear train in the ring USM design, its all done by vibrations (ultrasonic ones would you believe!)

 

I don't get it. I'm using a Sigma 10-20 which has the HSM and supposed FTM. But the AF is still physically detached from the manual focus ring - it seems like a kind of friction thing. So in servo mode, the AF is constantly working 'under' the ring meaning that I can never adjust the focus. Works fine in one-shot mode though, obviously.

 

My Sigma 150 macro, which is also FTM, will not allow FTM while in servo mode either... but it does on the other hand allow it in AI Focus and One Shot modes. That would lead one to believe HSM and USM are quite different mechanically. I am not completely familiar with the inner workings of AF and clutches so I can't really elaborate very much. Maybe Sigma should change theirs to PTM

 

I don't have the luxury of AI on my 300D so I never noticed the limitations of my 150 macro's FTM .

 

For me the use of FTM is to help the AF out in difficult situations, like shooting a bird through some branches, i spin to get the bird nearly in focus and then half click to get the camera to do the rest, without doing this it might grab one of the branches instead. I always shoot in AiServo and usually with a Canon 100-400 on a 350D.

The manual says FTM won't work in Servo mode, but when not half pressing you can still spin the ring, i guess what they mean is you can't half press and then correct the focus, but that's not something i'd want to do anyway.

 

I can still use FTM when AI Servo is selected with my 100-400 just as long as the shutter is 1/2 pressed...The same with my 70-200 as well.

 

I know what you mean especially with regards to the camera mode. I'm just saying that while you can adjust the focus manually while in any focus mode with the AF switch set to 'on' on the lens, pressing the autofocus button (which will be triggered by the shutter release without a custom function set) will re-focus the lens automatically anyways and override what you did manually.

Truth be told I don't really care. I can't focus nearly as accurately as the camera can, especially with the useless focusing screen in the 400D (I did briefly look into using a third-party alternative, but I'm hesitant for a number of reasons). I keep my camera in the AI Focus mode most of the time (I very rarely need servo mode, and AI Focus is really a hybrid of servo and one-shot anyways).