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Canon Rebel EOS T2

Hung Le , Nov 08, 2006; 01:11 p.m.

A) What for is the guide hole closed to the battery compartment chamber at the bottom of the camera?

B) Why do you need focus point selection while you can: 1/ Just use the center focus point to focus (i.e. the fastest and easiest way) 2/ Then recompose and shot

Responses

Steve Dunn , Nov 08, 2006; 02:09 p.m.

  1. I don't have a T2 and don't know for sure what hole this is. The T2 can take an optional battery grip; usually, battery grips have little pins sticking out of their tops which mate with corresponding holes in the bottom of the body, so my guess would be that that's what this hole is for.
  2. Why do you need multiple focus points if you'd prefer to do the focus-recompose-shoot dance, which (as has been discussed many times here) can mess up exposure (particularly for flash) and focus?

Mark U , Nov 08, 2006; 06:17 p.m.

Expanding on Steve's B answer a little:

http://www.visual-vacations.com/Photography/focus-recompose_sucks.htm

The problems become MUCH worse with close focus/macro work than with portrait work using wide apertures, where the slightest movement will invalidate AF.

It's also worth understanding that unless you are using partial metering or M mode, the camera's evaluative metering algorithm factors in the chosen focus point(s) (if you have all focus points active, several may be in focus at once) in deciding how to weight the readings from the 35 segments of the metering array. The algorithm is actually surprisingly sophisticated, but it will calculate the exposure based on the framing when you focus by half press of the shutter release - not the framing of your final composition - if you are in One Shot or AI focus mode.

Try a little experiment: have just a table lamp with a translucent shade on a table alongside you switched on in an otherwise darkish room. Using Av mode and One Shot focus, frame a shot so the table lamp shade lies under the extreme right or left focus point, but the centre point is pointing into the darker rest of the room. Set the centre focus point, and meter the shot using shutter half press (focus will be across the room). Now swing the camera so the lamp shade fills the frame, set focus and exposure from the shade at shutter half press, and recompose back to the original composition. Keeping the framing the same, set the focus point that is over the lamp shade, and re-meter the shot. You will get three very different meter readings.

If you used the focus-recompose method, the whole shot will be grossly underexposed because the metering was swamped by the bright lampshade. Using the correct focus point, the camera will endeavour to meter for the overall scene capturing the range between the bright and dark parts of it, while placing some emphasis on the subject focussed on. Note that for as contrasty a scene as this, partial metering wouldn't be useful (no mid tone to meter from), and guessing the right amount of exposure compensation might be quite difficult - you'd really need to take TWO partial readings and then set exposure manually between them - much easier to let the camera do the work for you.

AI Servo focus is a different case altogether - you HAVE to use the central point to pick up focus on your intended subject, but once the camera has started focus tracking the subject (which may take a second), if you have all focus points active, the camera will do its best to ensure that it maintains focus on the moving subject, even if it no longer lies under the centre point, and the camera meters and sets exposure when you press the shutter fully assuming you are in P, Av or Tv mode (a good reason why M mode is often best for action shots).

Hung Le , Nov 09, 2006; 09:22 a.m.

Thanks. You guys are really PROS, while I'm just a novice.

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