One should not recompose with an AF lock?

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satay16

Senior Member
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

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

ah.zeep

New Member
JediForce4ever said:
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...

satay16 said:
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

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

Andy Ang

Senior Member
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

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

sharp is sharp, oof is oof

Artosoft

Senior Member
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.

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