stupid question .. ....

[Kellyj69]

Ok .. I have a Rebel Xs with a 50mm f/1.8. when I'm shooting - usually in low light w/ no flash- I will press the shutter release and auto focus will kick in .. it focuses the shot.. but then NOTHING! It won't take the shot! If I'm in manual focus mode it will take whatever photo I want, I assume because it trusts me to know what is in focus ..

What am I doing wrong??

[Eastree]

It's because it cannot focus in low light. It keeps seeking something to focus on, but can't so it keeps seeking ...

In low light, it's better to use manual focus (though on DSLR viewfinders, it's much harder since they're made more for seeing what focus point is used, and for framing, than it is with a focusing screen actually made for manual focus).

And you're right: In manual focus, the camera assumes that you have chosen what you want in focus (basically).

[dcclark]

Probably what you think is "the camera focuses" is really "the camera tries to focus, and can't". This sounds exactly like focusing, but it's really just the lens racking in and out, trying to catch on to anything.

[jsherp]

The autofocus needs some sort of contrast in order to focus. If it is too dark, or there's not enough contrast, it will try and stop when it fails. Since it KNOWS it's not in focus, it locks the shutter button so you can't take a picture.

One trick I use is to find some contrast at about the same distance as what I'm trying to shoot, press the shutter halfway until the camera locks on that, then (holding the button halfway) move the camera to frame my original shot. If you guessed right, your camera will let you take the pic, and the shot will be in focus.