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Technique for best autofocus results
bigsnowdog
Registered Users Posts: 55 Big grins
I am a relative newcomer to autofocus. Essentially I have come from manual focus, film photography [Canon T90, since 1987] to autofocus ditigal with the Canon 40D. As an aside, I had previously a Canon G5, though I found its focusing ability to be unreliable.
What methods you use to achieve best focusing results?
How do you evaluate your focusing results in the produced image?
To what degree are you choosing to manipulate aperture as you consider your focusing?
How are you using the visible focusing points?
I suspect I don't have enough experience with this camera yet to ask the most focused questions, but I hope that much useful information can come from this thread.
What methods you use to achieve best focusing results?
How do you evaluate your focusing results in the produced image?
To what degree are you choosing to manipulate aperture as you consider your focusing?
How are you using the visible focusing points?
I suspect I don't have enough experience with this camera yet to ask the most focused questions, but I hope that much useful information can come from this thread.
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I most often use Av so DOF can be controlled, but most of my subjects don't move too much so shutter speed isn't the determining factor.
I seldom (never) use multiple focus points - I feel this gives the camera too much control for its intelligence level.
As much as possible (exclusively on closeup work), I use the same techniques I used with my last "real" cameras - Pentax S and Canon A-1 (both manual focus). I carefully adjust the diopter wheel to make the black squares as crisp as possible, turn AF off, and (while on a tripod) carefully adjust the focusing ring to achieve focus on the part(s) of the image that I want to accentuate.
For more distant objects, I resort to AF, but with the focus on the * button, I can focus on something that's "at the right distance", and re-compose the image. However I must always be aware of the "focus-recompose" inaccuracies.
When taking photos of people I always aim for the eye as that is where I want the sharpest focus.
I have a hard time seeing if what I am getting is really in focus if I go manual. Especially if working under a time pressure and trying to capture candid images.
I always adjust apeture based on enviromental needs but also know with each of my lenses there is a sweet spot for sharpest focus. When possible and where focus is critical I work my settings to keep in that apeture range. This will vary some with each lens so you need to know your lenses.
"Look, I'm not an intellectual - I just take photographs." -- Helmut Newton
Focusing strategy depends a lot on what you are shooting and I do use different techniques in different circumstances. That said, for most of my shooting move the the focus to the * button (a C.F. on the 5D) and leave only the center point enabled. As a rule, I only let the camera make decisions for me when I know I won't have time to make those decisions myself (that includes focus and exposure).
I don't know what you are meaning by this button remark.... would you explain that?
I don't have the 40D manual, but in the Custom Functions, there is a setting wherein the focus can be assigned to the "star" button (*) on the back. It will be under your right thumb as you hold the camera.
By using this setup, when the shutter button is half-pressed (the "normal" focus method), the focus will not change - it is controlled by the * button. Thus the shutter button is only used to release the shutter and doesn't control the focus.
At first it may be a bit awkward, but I would estimate that 99 percent of people that try this method, stay with it.
One of the advantages is that when using AI Servo, one can hold the * button down to track a moving subject and trigger the shutter when desired with the index finger. The exposure reading is only taken when the shutter button is depressed.
On the 5D, the function is C.Fn-04 Shutter/AE Lock and the setting I use is AE Lock/AF. The funcution number is likely different on the 40D, but the behavior is likely the same. The way this functions is named is really confusing, but the net effect is that the auto focus is moved from the shutter button to the * button (which you press with your thumb). In this mode, the camera acts essentially like a manual focus body because the focus will stay where you set it from shot to shot. However, if you want to use auto focus, just point the center dot at your target, press the * button and you are focused where you want to be. Give or take a bit, you can use the AF system as a faster and more accurate replacement for the split prisim on your T90.
Great tip. It inspires me to go back to my own manual and explore other settings and functions I have missed as well.
"Look, I'm not an intellectual - I just take photographs." -- Helmut Newton