The AF points only light up red when:
- Selecting an AF point or points.
- Starting AF and achieving focus lock in One Shot focus mode.
- Starting AF in AI Servo focus mode.
On that camera, there should be small black squares or rectangles indicating the approx. position of each of the AF points, and the red dot within each of these lights up in the above situations. I don't know why they would be hard to see. Maybe it has to do with the lens being used (a lens with a smaller aperture such as f5.6 makes for a less bright viewfinder than a lens with an f2.0 or f1.4 aperture). Or, maybe it has to do with the diopter adjustment (used to dial in the viewfinder for your particular eye). There's also a "Viewfinder Extension" accessory that tends to make the image in there smaller and harder to see (but moves your nose away from the LCD on the back of the camera). If the seller has one of those on the camera, it would make it harder to see the red dots, too, I imagine.
On some cameras you can turn those red LEDs on or off... I'm not sure if the XSi/450D is one of those models. I'm also not sure if any of the cameras have an adjustment on their brightness (either set manually, or automatically based upon the brightness of the scene).
Maybe something just needs cleaning... Or it's possible there is an actual fault with the camera that's causing those red LEDs not to be very bright.
Note: Some of the newer camera models - 7D, 70D, 5D Mark III and 1DX - have an "active matrix" transmissive LCD focus screen that doesn't even have those red dots in the AF points. Some find that a little disconcerting at first, coming from one of the other camera models, but soon get used to it. So you might find it okay to use the camera without those little red LEDs being very bright
***********
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM .
