One should not recompose with an AF lock?

[satay16]

Many photographers do this. They want to take Subject A, but A is somehow hard to lock focus on(perhaps due to low contrast). So, photograhers focus at Object B, an object which is the same distance as Subject A from the photographer. So, after locking focus, they recompose back to A, and take the shot. At the end, a nicely well-focused photo.

"Not so," says Michael Hohner. He gives his explaination of his statement here: http://www.mhohner.de/recompose.php. However, after reading it a couple of times, I still dun get it. How can A be still in focus when you recompose back to B? Is he wrong?

[JediForce4ever]

As long as both subjects are of the same distance from the film/sensor, both will be in focus.

[ah.zeep]

Originally Posted by JediForce4ever As long as both subjects are of the same distance from the film/sensor, both will be in focus.

TS's link points out mathematically that even if points A & B are at the same distance, they will not both be in focus...

Originally Posted by satay16 Many photographers do this. They want to take Subject A, but A is somehow hard to lock focus on(perhaps due to low contrast). So, photograhers focus at Object B, an object which is the same distance as Subject A from the photographer. So, after locking focus, they recompose back to A, and take the shot. At the end, a nicely well-focused photo. "Not so," says Michael Hohner. He gives his explaination of his statement here: http://www.mhohner.de/recompose.php. However, after reading it a couple of times, I still dun get it. How can A be still in focus when you recompose back to B? Is he wrong?

I think your points A & B is swapped from the ones described in your link. In his link, he uses Point A as the reference and B is the intended (recomposed) scene. Your description is the other way round.

So his math treatment says that the final (recomposed) point B will be sharp, whereas the one he used for focus lock (point A) will not be sharp.

I think what he says makes sense if one chooses points A and B that are far apart. If not so far apart, then hopefully there will be enough depth of field such that both A and B will be in focus...

[zcwnfx]

actually could be almost in focus right? cos focusing is about focal distances and such...

[Andy Ang]

It also have to depends. If the subject is near the hyperfocal distance, it wont be affected so much. Only macro shots / adverts needs for the precision. They need to even know how far is the object is from the film / sensor of the camera.

[ortega]

just take the shot and use your eyes to see lor
no need to be so calculative

sharp is sharp, oof is oof

[Artosoft]

You must know which one need to be sharp. For example: human portrait, sharp from DoF and blur movement. Just their eyes sharp will lead people to think the photo is sharp (of course to some extern).

Regards,
Arto.