One should not recompose with an AF lock?


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satay16

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Jan 14, 2006
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#1
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?
 

ah.zeep

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Jun 20, 2006
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#3
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
Jun 6, 2005
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Potong Pasir
#4
actually could be almost in focus right? cos focusing is about focal distances and such...
 

Andy Ang

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Jan 10, 2006
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Dreamy Nikon Land
#5
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.
 

Artosoft

Senior Member
Aug 31, 2005
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Tanjong Katong
#7
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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