I have a question for those who own the pro bodies i.e 1D MK11 etc. From everything i have read over the last few years i consistently see the recommendation to use center focus point and that seems to apply whether its a 10D, 20D, 40D or 1D etc. My understanding with the pro bodies is that there is more focus points ie 45 but what value is there in having 45 focus points if 99% of the time you use the center one ? My other question is why are the focus points not more uniformly distributed to enable off center compositions ?
I haven't used a 1 series body but i am curious to get a more detailed understanding of under what circumstances the auto focus is superior to non pro bodies.
I think the 45 points are distributed well for off-center subects. I rarely use only the center point...focus and re-compose, that some folks use, is too unreliable. And I have expansion turned on, so if AF can't be achieved with the selected point it will expand to achieve focus...this is helpful with AI Servo and moving targets that may drift off my selected point.
The focus point to use, expand or not expand is going to be subject specific. In some cases all 45 in auto (ring of fire) works for airplanes against sky, birds against sky, etc. For field sports, center and expanded usually works well. If you shoot vertical, and "rule of thirds", select a AF point at the edge of the AF elipse. Long story short, as you use the camera, you will find what works for you.
Depends on the subject, specifically on the orientation of its main linear contrasts.
What most people don't seem to realize is that the outer focus points (those that are not "cross type" focus points) are totally blind to linear contrasts that run parallel to the orientation of the rectangle.
If you try to use a non-cross-type focus point on a subject that has lines running parallel to the rectangle, it will fail to focus. The reliability of focus will increase as the linear contrasts move from parallel to perpendicular.
So people experience various levels of reliability with them, unless they are aware of this issue.
RDKirk wrote:
Depends on the subject, specifically on the orientation of its main linear contrasts.
What most people don't seem to realize is that the outer focus points (those that are not "cross type" focus points) are totally blind to linear contrasts that run parallel to the orientation of the rectangle.
If you try to use a non-cross-type focus point on a subject that has lines running parallel to the rectangle, it will fail to focus. The reliability of focus will increase as the linear contrasts move from parallel to perpendicular.
So people experience various levels of reliability with them, unless they are aware of this issue....Show more →
Very good comment for the MKII, but on the MKIII all selectable points are cross point at f2.8 and faster.
with Ai focusing there is a better chance to catch your subject correctly if the camera has 45 spots to choose from. In manual mode, selecting the spot you want becomes more of a problem and you have to weigh the difference between using the appropriate spot in your frame or just focus and recompose... depends on your subject and conditions. For me, (unless I'm shooting my EOS 3 with eye control) focus and recomposing generally works better since it if faster in dynamic situations... just have to accept the minor problems (vertually non-existant at f2.8 and above).
