Focus Questions????

Can someone please clarify this for me?
I'm using the center focus point 99% of the time.
If I focus on a specific part of an iage-then hit the focus lock button-then recompose ,will the original part of the image I focused on be in sharp focus?

I tried to do this yesterday and when I opened the image in Zoombrowser,the center point was highlighted in red,but some of the other focus point were in black.
Am I correct that the camera used the one in red??
Any help would be appreciated
Mike

Q1, yes

Q2, yes

Sandro,
Thans for your reply.
If that is the case ,why Is the part I originally focused on...in one of the BLACK focus points
Please correct me if I'm wrong?
Mike

If you recompose after focusing, the center AF point moves, also. But if you held the shutter button partially down while recomposing, your original point should still be in focus.

Also, you may want try using the closest focus point to your suject rather than trying to use the center point and recompose a lot. I get better results this way.

OK ,got it....
I did not hold down the shutter button when I re-composed.
Thanks for clarifying.

Tmonatr-thanks for your reply.
OK,thanks for the tip.

Mike

Mike

My understanding is that DPP will show the active focus point square in RED. So lets walk this thru. You pick a person and put the center focus point on his EYE. Holding the button down steadily, you recompose so that the eye is not in dead center any longer, then finish pressing to fire the shutter. When the shutter fires, the red focus point is actually on his shoulder (or whatever). The eye should be in focus, but the red square has moved to the shoulder. DPP is only showing you what you did, as focus lock is only achieved once, as long as you keep steady pressure on the button. Pulse your finger, and the camera will refocus as if the original focus lock never occurred.

There are two potential problems with this method. Both these problems could be seen clearly if the eye of your subject (or whatever you selected as the original focus point) is not in focus.

1. You did it wrong. Meaning that you accidentally pulsed your finger onthe shutter button. Easy to do.
2. You did it right, but the eye is still out of focus. HUH? This is actually fairly easy to do. If you are using a thin DOF (large aperture- indicated by a small aperture number), as you recompose, you are changing the angle of the line of sight, thereby either increasing or decreasing the distance between the camera and the subject. If the change in distance is more than your DOF, you can knock out the focus of the subject.

There is some math involved here, but think it thru. Stand in front of a wall. If you walk straight ahead, the distance between your nose and the wall is 6 feet (for example). If you walk to a corner of the wall, it could take you 7 feet or more to get there. Now apply that to the camera. It focussed originally and very precisely on a target 6 feet away. By changing the angle, but not changing the focus, your subject is now 7 feet away, and thus out of focus.

I hope this is helpful to you

1. Not necessarily. It depends on depth of field. If you are close enough to the subject (small DOF) recomposing causes original point of focus to move off the plane of sharpest focus.
http://www.visual-vacations.com …focus-recompose_sucks.htm

2. Not sure how useful zoombrowser info is in this case. You know that you recomposed, so the highlighted points are no longer actual focus points.

Regards,
Lev

Richard_Miami wrote in post #4012035
Mike

My understanding is that DPP will show the active focus point square in RED. So lets walk this thru. You pick a person and put the center focus point on his EYE. Holding the button down steadily, you recompose so that the eye is not in dead center any longer, then finish pressing to fire the shutter. When the shutter fires, the red focus point is actually on his shoulder (or whatever). The eye should be in focus, but the red square has moved to the shoulder. DPP is only showing you what you did, as focus lock is only achieved once, as long as you keep steady pressure on the button. Pulse your finger, and the camera will refocus as if the original focus lock never occurred.

There are two potential problems with this method. Both these problems could be seen clearly if the eye of your subject (or whatever you selected as the original focus point) is not in focus.

1. You did it wrong. Meaning that you accidentally pulsed your finger onthe shutter button. Easy to do.
2. You did it right, but the eye is still out of focus. HUH? This is actually fairly easy to do. If you are using a thin DOF (large aperture- indicated by a small aperture number), as you recompose, you are changing the angle of the line of sight, thereby either increasing or decreasing the distance between the camera and the subject. If the change in distance is more than your DOF, you can knock out the focus of the subject.

There is some math involved here, but think it thru. Stand in front of a wall. If you walk straight ahead, the distance between your nose and the wall is 6 feet (for example). If you walk to a corner of the wall, it could take you 7 feet or more to get there. Now apply that to the camera. It focussed originally and very precisely on a target 6 feet away. By changing the angle, but not changing the focus, your subject is now 7 feet away, and thus out of focus.

I hope this is helpful to you

Nice one, Richard. Very good explanation.

Richard_Miami wrote in post #4012035
It focussed originally and very precisely on a target 6 feet away. By changing the angle, but not changing the focus, your subject is now 7 feet away, and thus out of focus.

This doesn't sound right - if you only change the angle the subject is still 6 feet away. I.e. you are in the center of a circle with radius 6 feet, the subject is at a point of this circle. If you rotate the camera you are still in the center of that circle. The problem is that the plane of focus (tangent to the circle) is no longer passing through the original subject.

Regards,
Lev

lev888 wrote in post #4012825
This doesn't sound right - if you only change the angle the subject is still 6 feet away. I.e. you are in the center of a circle with radius 6 feet, the subject is at a point of this circle. If you rotate the camera you are still in the center of that circle. The problem is that the plane of focus (tangent to the circle) is no longer passing through the original subject.

Regards,
Lev

Sorry if I wasn't clear enough. The subject I refer to is the subject of the selected focus point, not the entire person. Also, please remember that this is affected by your chosed DOF (aperture).

Think of shooting a bird. The bird is the subject of your photograph. You put the focus point on his eye, making his eye the subject of the focus. The focus point knows nothing about the eye - it only knows the distance between the sensor and the item in the red box.

Now add that your aperture is something large, like f/2.8 - because its not good lighting. Depending on your distance from the bird, your DOF may only be a few inches or less.

When you recompose, but keep the focus point locked, you may have moved his eye a few inches away from you or closer to you -due to the changing angle - thats all it takes. The camera will not refocus, but will click, and anything that is exactly as distant as the eye originally was will be in focus, but not the eye itself.

I hope that helps.

Depending on your DOF, if you focus lock and recompose, you may or may not cause your subject to be out of focus; as others suggested, use the closes focus point to your subject and this becomes a mute point.

Richard_Miami wrote in post #4012861
When you recompose, but keep the focus point locked, you may have moved his eye a few inches away from you or closer to you -due to the changing angle - thats all it takes.

Sorry, don't see how the distance changes. Let's do a 'thought experiment'. Tie a string to the bird and attach the other end to the tripod mount (it's at the focal plane of the camera). Its length is 6 feet. Now recompose. Since you are only changing the angle you are still 6 feet away from the bird, attached by the same string. Please let me know what I'm missing.
Regards,
Lev

Lev
I am doing a lousy job of the details. I think the link you provided says what I am trying to say, but much better than I can.


This is what happens when I try to think thru this stuff while at work..sigh