Fail to focus properly in low light. :(

Sorry if i posted in the wrong section.

Hello fellow POTN-er. Your help is greatly appreciated.

Ok guys, here's my setup.
Canon 550D/T2i
EF 70-200mm f4L IS USM
And a flash.

I just wanted to seek clarification whether is it normal for AF to go haywire in low light?
Just moment ago, i was shooting a indoor prize presentation event. It's kind of like reddish-yellow lighting. Not really bright or dim.
I shot with this setup with setting of 1/50s , f4 , ISO 400 , WB:Flash

When i look at my photos i have taken in my camera, it looks kind of sharp to me (Just a second). Did not really go into detail. As i worry my focus may go wrong, every photo i've taken, i re-focus.

However, now when i look at the photos in computer, i see many photos were wrongly focused. is it lens problem? or camera problem? or its normal?

Example
i focused at the guy on the left but it seems like the word is more sharp.

Relying on AF in poor light can be an exersize in futility...you may want to aim for more DOF and of course increasing the ISO to compensate.
Go to Canon's website to learn about AF for your camera.

Thanks for the advises.
Because i'm afraid my photo will be noisy as from ISO 1600, i can see grainy even in camera itself.
I thought people would go widen the F-stops for more light and that's why chose f2.8 instead?

Sorry for any ignorant question.

What mode? Single point AF or are you letting the camera choose?

Looks to me like the first one just chose the podium, but interestingly enough looking at it close, the guy on the right doesn't look so bad. Maybe the guy on the left was moving a bit, or more likely, saw the 70-200 swing up like the mighty battle axe it is, and you startled him. Good thing he was rewarded with instant blindness for a few moments!

Second one looks like camera shake to me.

sometimes a grainy picture is better than one that is out of focus or blurry..besides, the noise reduction in some of the newer software is pretty dang good...I would do as suggested and stop down the aperture and boost the ISO...
If you were shooting 2.8 at ISO 400 then f/4 at 800 ISO would give you the same exposure but with more depth of field..
the T2i should handle noise decently..I shoot 1600-3200 all the time on a 5D and I am sure noise handling is improved in a T2i over a 5D

JDPhotoGuy wrote in post #14670210
What mode? Single point AF or are you letting the camera choose?

Looks to me like the first one just chose the podium, but interestingly enough looking at it close, the guy on the right doesn't look so bad. Maybe the guy on the left was moving a bit, or more likely, saw the 70-200 swing up like the mighty battle axe it is, and you startled him. Good thing he was rewarded with instant blindness for a few moments!

Second one looks like camera shake to me.

Hahas.. that's humorous..

I using single point AF for this as i want a exact focus.

Yea, it does looks like camera shake to me for the second one as i was continuously shooting for a few hours. but to me, i think wrong focus is more serious than camera shake though. it's just a example i pick it up from my recycle bin.

bdpaco wrote in post #14670215
sometimes a grainy picture is better than one that is out of focus or blurry..besides, the noise reduction in some of the newer software is pretty dang good...I would do as suggested and stop down the aperture and boost the ISO...
If you were shooting 2.8 at ISO 400 then f/4 at 800 ISO would give you the same exposure but with more depth of field..
the T2i should handle noise decently..I shoot 1600-3200 all the time on a 5D and I am sure noise handling is improved in a T2i over a 5D

True. thanks for the advises.
Do you do event shooting also?
May i know what aperture you all/photographers usually use in this type of event?

I have friends in bar bands that I do some shooting for from time to time...settings constantly change because of lighting, f/4 at 800 ISO and adjust that as I need to to get a shutter that will stop action and keep me from getting any motion blur, unless of course I want some...If the venue is crazy dark or I want to kill the crazy lighting they use sometimes I will throw a 550EX on and bounce it off the ceiling or a wall...

So it seems that f4 is still too shallow for me?

LamboSan wrote in post #14670269
Hahas.. that's humorous..

I using single point AF for this as i want a exact focus.

Yea, it does looks like camera shake to me for the second one as i was continuously shooting for a few hours. but to me, i think wrong focus is more serious than camera shake though. it's just a example i pick it up from my recycle bin.

Single point is also more reliable in low light, so you're good there. Front/back focus is by far a more serious issue. However, it's not usually the fault of the camera. Once you do more events like this, you'll figure out what your camera wants YOU to do to make it take good pictures. Then you can make it perform with consistency.

I hope so too.. i know i still got a long way to go as a photographer... Thanks..

^ I know this may be a silly question, but where on the subject are you usually putting the focus point before you recompose ? I mean, we know how AF systems work--they look for areas of contrast, so eyes are good, zippers, reflective areas like glasses. What may be happening to you is that while you're trying to lock focus on the subject there is something super contrasty nearby (glare off the podium e.g.) that snags it instead.

One tactic might be to 1) lock focus on the subject 2) put lens to Manual mode 3) chimp shot on screen by zooming to check if it's alright 4) if it is, continue shooting in manual (and not moving or zooming of course). I often use the back-button (set up in Custom Functions) instead of shifting to manual mode.

i usually set the focus point to center of the frame and recompose it them a bit. If they were far away from the center part, i usually change to the nearest focus point.

2) u mean manual focus? thanks for the advises. i can try that 1 day if there's any more event.

Ah. I recommend always using centre point in low light--it will yield the best results in most cases (not to say other points are terrible). And I recommend setting the point on the face, especially the eyes, glasses, as I suggested--then recompose.

Yes, I mean manual focus--You would do this to keep your lens focusing at the same distance once you've established it's right on.

Thanks alot..

LamboSan wrote in post #14670174
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I thought people would go widen the F-stops for more light and that's why chose f2.8 instead?

Sorry for any ignorant question.

get a little closer, use manual mode at f4 or f5.6, 1/100, ISO 800 with ETTL flash = nice sharp pics