EOS 300 Focussing point/AE Lock/Partial Metering

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hello all :-)

i have a couple of doubts on focussing points and AE Lock/Partial metering..rather about HOW and WHEN they will be used...these are in context of the Canon EOS 300/Rebel 2000..I use it mainly in manual mode..sometimes in Av/Tv mode..

1. I understand that i can manually select which focussing point i want to give priority to by pressing the "focus point selection button" and rotating the command dial. this is to be used when the subject or rather the area from where i need to pick up the reading is not exactly in the center of the frame. correct so far ??? but even when i use the default 7 point system without selecting one of my own, (where all 7 points are selected)can i not first aim at my subject, adjust settings and then recompose and shoot ??? even in manual as well as AE modes rite ???

2. i understand that partial metering covers 9.5% of the central area in the viewfinder. how different is this from instead using the focus point selector to set the central focus point as the active focussing point ??? is it that even if the central point is chosen, centre-weighted average metering will be used ?

3. what happens if i choose partial metering AND also select manually select a focussing point..say for eg the one on the extreme left ??

4. i understand the AE Lock button also doubles up to activate partial metering ??? what exactly is AE LOCK ??? is it the same as pressing the shutter half way to store the readings and then recomposing ??? when i press the AE Lock/Partial Metering button, how do i know what is working-the AE Lock or the Partial Metering function ???(i know this is ONE messed up question)also is this AE Lock/Partial Meter thing dependant on the mode u r shooting in ???

thanx in advance friends...

ciao venkat

-- Venkat (venkat_p_iyer@yahoo.com), January 15, 2002

Answers

"1. I understand......correct so far ???" - So far, so good.

"...can i not first aim at my subject, adjust settings and then recompose and shoot ??? even in manual as well as AE modes rite ???"

In manual mode this will work. I don't remember about the EOS 300/Rebel 2000, but in some other Canon cameras the shutter button hold the AF distance but it won't hold the exposure value. You have to press the AE Lock button to do that.

"2. i understand that partial metering covers 9.5% of the central area in the viewfinder. how different is this from instead using the focus point selector to set the central focus point as the active focussing point ???"

Setting the AF to center point does not force metering exclusively from the center point. It will still default to Evaluative if you are not in manual mode (but it is bised towards the center area if the center AF point is chosen). Or it uses center weighted averaging in manual mode. Neither of those are the same as partial metering. Partial metering meters the central 9.5% exclusively. The other modes still consider the outer areas.

"is it that even if the central point is chosen, centre-weighted average metering will be used ?

"3. what happens if i choose partial metering AND also select manually select a focussing point..say for eg the one on the extreme left ??"

In manual mode only, the camera uses center weighted averaging, no matter what AF point is chosen.

"4. i understand the AE Lock button also doubles up to activate partial metering ??? - Yes

"what exactly is AE LOCK ??? is it the same as pressing the shutter half way to store the readings and then recomposing ???"

Check it. Does the exposure stay the same when you hold the shutter button down in P, Av or Tv modes? Obviously in manual mode nothing changes since you control the exposure yourself. Pressing the AE Lock button holds the exposure value for several seconds (16?) and activates partial metering.

"when i press the AE Lock/Partial Metering button, how do i know what is working-the AE Lock or the Partial Metering function ???"

Both

"...also is this AE Lock/Partial Meter thing dependant on the mode u r shooting in ???" - You have to be in P, Av, Tv or M

-- Jim Strutz (j.strutz@gci.net), January 16, 2002.


Jim has given a very good description of what happens. i would just like to add my experience with EOS 300/R2K. By pressing the AE lock button, you lock the exposure values (shutter speed and apperture values) depending on the partial metering at that instance. later when you recompose the shot and press the shutter button half way to focus the same EV is maintained for 6 sec. ( or may be something else, i don't remember the exactly). i used mainly in Av mode and very rarely Tv and M mode unless i need center weighted averaging metering. but as far as i think, the focusing point selection is nothing to do with the AE lock button in any modes.

The best way to know how this works is to focus on something which is bright at the center, use AE lock, recompose and focus on something else (possibly off centered object) in all creative modes and study the correct exposure values. you will learn a lot.

-- sajeev (chack74@yahoo.co.in), January 16, 2002.


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