T2i (550D) Low Light focusing

At a family event I noticed I was having problems achieving focus in low light using my 550D and YN-468 Flash. Generally everything worked well but every now and then my camera wouldn't fire the shutter because it hadn't obtained focus...I could see the red light from the flash being activated on half press....but is this issue just bad luck because of the subject lighting or is it indicative of a fault in my flashgun or camera or could it be due to weakening batteries in the flash....I missed a few shots due to this problem, people will not wait for the photographer to get his gear sorted so I would like to ensure that I can minimise if not avoid these problems in the future....any ideas to try out would be appreciated.

Not trying to talk down on the equipment, but that is what separates a better AF system in higher end bodies. Sounds like it was too dark for the t2i to obtain focus. Maybe use faster glass (2.8) or higher.

birderman wrote in post #15064969
At a family event I noticed I was having problems achieving focus in low light using my 550D and YN-468 Flash. Generally everything worked well but every now and then my camera wouldn't fire the shutter because it hadn't obtained focus...I could see the red light from the flash being activated on half press....but is this issue just bad luck because of the subject lighting or is it indicative of a fault in my flashgun or camera or could it be due to weakening batteries in the flash....I missed a few shots due to this problem, people will not wait for the photographer to get his gear sorted so I would like to ensure that I can minimise if not avoid these problems in the future....any ideas to try out would be appreciated.

not sure what to say, with the focus assist from my flash - no matter how dark, my t2i is always able to obtain focus. which lens are you using? does your flash have a focus assist? i'm not familiar with your model.

the nicer canon flashes include an AF-assist beam to help with focusing in low light. my 430 used to help quite a bit before I moved to a higher end body.

The AF assist of the referenced flash, according to one test, just doesn't measure up to a Canon flash.

The 430 EX II's AF assist is a red/IR grid beam that is designed to line up perfectly with Canon's AF sensor points. With my 60D I can focus on a black dog in a black room and get a perfect lock. I don't think the AF assist on those flashes is as good as the Canon's. If you are shooting professionally doing events I would highly recommend the 430 EX II, it is an excellent flash.

Not really a body problem - much more to do with lens/flash, IMO. If you were using a lens such as the Canon 50mm f/1.8 with the YN flash, it's gonna hunt!

The YN-468 has red beam for focus assist, the lens was standard kit 18...55 . It was only some shots that proved difficult, generally it worked quite well. But reading the responses so far I guess its a combination of things: ie speed of the lens, focus system of the body, reflectivity/colour of subject etc. I guess until I can justify expense of more higher end gear I will have to put up with these issues.

not body. lens/flash, but more so flash.

birderman wrote in post #15068625
The YN-468 has red beam for focus assist, the lens was standard kit 18...55 . It was only some shots that proved difficult, generally it worked quite well. But reading the responses so far I guess its a combination of things: ie speed of the lens, focus system of the body, reflectivity/colour of subject etc. I guess until I can justify expense of more higher end gear I will have to put up with these issues.