focusing in low light

[jli]

What techniques are there for getting sharp pictures in low light? I can only think of the following two:

1. Use external lighting so you can narrow down the aperture enough to get almost everything in focus.

2. Use manual focus.

(1) is not ideal because it requires equipment that must be bought, moved, set up, etc.

(2) is also not so great because MF is already hard to do with good light. With low light, trying to get everything sharp through the tiny viewfinder is really hard.

However, I get really annoyed when my AF just grinds back and forth slowly and finally completely fails in low light. Sometimes it's not so bad, and AF works on the 2nd or 3rd try. But do people often resort to MF, settling with getting a slightly soft shot vs. no shot because the AF fails?

Also, I have a 1000D/Rebel XS with just 7 focus points. I understand the higher-end models have 15x more (or whatever :P), but it seems like simply having more focus points wouldn't help if I'm using just the center point. Do the higher-end models actually have faster and/or more accurate AF?

I mentioned this in another thread on focusing - my dad's old SLR's viewfinder has this darker rectangle and a smaller circle in the center. The circle seems textured, or sort of fuzzy. When changing the focus, the image in the circle changes more dramatically so it's very easy to tell when the center is in focus. Why isn't this included in modern SLRs (I'm assuming this type of viewfinder isn't included in the higher-end models)? Do they just hope AF will be good enough?

Thanks!

[inkista]

Originally Posted by jli

...
2. Use manual focus.

3. Use Liveview and 10x magnification with manual focus.

Do the higher-end models actually have faster and/or more accurate AF?

Yes, but mostly in terms of tracking moving objects. But also which lens you're shooting with can affect AF performance. Remember, the AF system needs light to "see" by. The larger the max. aperture of the lens, the more light comes in.

I mentioned this in another thread on focusing - my dad's old SLR's viewfinder has this darker rectangle and a smaller circle in the center. The circle seems textured, or sort of fuzzy. When changing the focus, the image in the circle changes more dramatically so it's very easy to tell when the center is in focus. Why isn't this included in modern SLRs (I'm assuming this type of viewfinder isn't included in the higher-end models)? Do they just hope AF will be good enough?

The reason the split-circle focus screens are no longer standard is that they make the viewfinder darker. When autofocus systems were put into SLRs, the system needed light to "see" by to set the autofocus and to set the auto exposure. The mirror that used to be 100% silvered to throw all of the light from the lens up into the viewfinder became half-mirrored, so that light went up into the viewfinder AND to the film/sensor plane. But this resulted in a darker viewfinder. Dimming it even further with a split circle didn't help matters. So, matte focus screens became the default.

You can replace the standard focus screen with one that has a split circle in it, but it's a rather delicate and PITA operation in the XS, and dRebel models. The 40D/50D and above bodies have interchangeable focus screens--except for the 7D (the new LCD overlay in the 7D's viewfinder means the focus screen is now wired into the camera, not just a little piece of plastic that can be swapped).

There are a few things you can do to help your camera AF in the dark. You can use a faster lens. You can aim for something with higher contrast (i.e., where a sharp edge of something white meats something dark). You could use a flashlight to light your target before focusing. You can use liveview and manual focus. And you can stop down to get more DoF while stabilizing the camera on a tripod. Or add more light to the scene using an external flash, or just opening a window shade or turning on another light.

Cameras simply aren't as sensitive to light as our eyes are.