Using focus points in a Canon DSLR

Hi! I've got both the Canon 10D and just picked up a 20D with 9 focus points. Up to now

I've always just selected the center focus point and re-framed my images. I shoot some

weddings and also shoot landscapes for fun. Typically, I shoot with "one shot" focusing as

well, but am thinking of trying out the "AI focus" more. Anyways, my question is whether

letting the camera select the 9 focus points is sufficient and accurate enough for shooting

weddings and for portraiture. It seems like if you're shooting with a shallow depth of field

for bokeh why trust the camera to select your focus point. Do you find that the points

selected by the camera are accurate enough? I'm sure 1D owners have much more to say

about this since they have 45 points to choose from. Any thoughts or comments would be

much appreciated. Thanks!

I never use 45 points. I select a single point virtually all the time but that's not best for

everyone. Shooting moving birds against the sky for instance might be better using several

focus points. For weddings and portraits you definitely don't want the camera choosing

the focus point.

Hi Andrew,

 

One of the really nice features on the 1D is in the review menu it will show you which

focus points were active, takes a lot of the guess work out off the equation, I like this

feature as much as the blown highlight indicator.

 

For weddings and portraits I normally pre compose and then choose a focus point to suit

before going to take the pic, on the 1V and 1D I'll often reduce the selectable number

down from 45 to a more managable number. In general photography, landscapes etc I

found the auto select to be quite good, basically it will focus on the closest thing with

contrast within the focus points.

 

Take care, Scott.

When I've let the camera choose the focus point it's made some pretty strange decisions, but almost always whatever is closest.

 

I do center focus, recompose, shoot in practically all cases

Do you guys use the "one shot" mode, "AI focus" mode or "AI servo" mode?

One nice feature of the 20D is the little joystick that you can use to instantly select the

focus point. I tried it out for a bit and it looks like it can work out pretty well. To center

the point you just press the joystick down. It's much much faster than scrolling through

each focus point with the wheel and button. If you manually select the focus point like I

do it seems like a great intermediate option between using just the center point and

letting the camera select your point.

I found on the 10D that auto focus point select consistently picked the wrong subject.

 

Note that flash (on a 10D, not the ETTL2 based 20D) is based on the active focus point. Letting the camera choose for you would be disasterous.

<I>"Do you guys use the "one shot" mode, "AI focus" mode or "AI servo" mode?</I><P><P>

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00A953

I manually select the focus point closest to what I want in focus, thus the reframing is to a miminal.

On the 45-point cameras, in AI Servo mode and with automatic choice of focusing point, focus is acquired with the central focusing point and then tracked using all 45, so you can follow, say, a moving bird or aircraft without needing to keep the central point on it. If 45-point coverage is too much, then CF-17 allows more limited expansion of coverage around a chosen point, with the chosen point being used if possible. In my as yet relatively limited experience with the 20D, you have to work much harder at keeping the central focusing point on the subject.

"Note that flash (on a 10D, not the ETTL2 based 20D) is based on the active focus point. Letting the camera choose for you would be disasterous."

 

I think Jim has it backwards: where flash is based on the active focus point, the focus and re-compose method is more likely to lead to disaster. Also, isn't evaluative metering also biased toward the active focus point?

Two comments:

 

1) there is a rather nice setting on the 1-series cameras (45 focus points) that lets one

limit the choice to 9, and then set the back dial to cycle through ALL of them without

pushing anything else...

 

The technique is: point, 1/2 push, rotate to the point you want, shoot - VERY fast.

 

You can revert to auto (all 45) by pressing the focus point selector while the shutter is half

pressed.

 

2) focus recompose is the *source* of a lot of 'back focussing' you will hear people

complaining about - to understand this,

 

- take a square (the L-shaped thing you use for setting a 90deg angle)

 

- sight down it so that you are viewing something at the 90% corner

 

- imagine that this would be in focus at the 'centre' point

 

- rotate the square so that the opposite corner is now where you were looking - that

would be the right (or left) focus point

 

- note *surprise* that it is BEHIND / further away than where you focussed

 

- this is because you are rotating the plane of focus when you recompose.

The square simply shows that your line of sight and the plane of focus are

90deg to each other

 

As long as the hypoteneus is longer than the base of a triangle this technique will lead to

'back-focussing' LOL

 

cheers, m

"I think Jim has it backwards: where flash is based on the active focus point, the focus and re-compose method is more likely to lead to disaster. Also, isn't evaluative metering also biased toward the active focus point?"

 

Actually, for ETTL (not ETTL2) Flash photography BOTH focus recompose AND autofocus point will lead to disaster. For ETTL flash, the active focus point MUST be on the subject. Not only that, but the focus point must be a neutral (like, 18% grey!) colour.

 

The problem with autofocus select is that the camera selects subjects based upon distance/contrast. Not colour neutrality. If the camera selects a nice bright button on a white dress: Disaster!

 

If you focus recomponse based on a nose, then move the focus point to a white dress: Disaster!

 

With ETTL, you must CHOOSE the focus point, and place it on a neutral balanced subject at the distance you want. Usually, a pretty girl's eyes work fine. Can't make that work? They you must use flash exposure lock.

 

Now, with ETTL2, evaluative metering is used (just like ETTL) for flash. The difference is that the focus point is NOT so highly emphasized like it is with ETTL. That way, if the focus point winds up on a white wall OR a black tux. . .the flash shot still works.