Focal Length vs DOF: Revisited

[jamesino]

So far, I've been comfortable with my knowledge of the Depth-of-field effect of photography. The DOF is solely a factor of the focal distance and aperture, except in Macro photography, where the pupil magnification also plays a factor.

Most tutorials say that the focal length does not technically effect the DOF because if you were to keep the object the same size, you will see the same DOF as a lens of a different focal length. For example, if you were to take a picture of an object from 10m away with the same aperture, one with a 50mm lens and the other with a 100mm lens, the 50mm lens will look like it has a greater DOF. But if you were to keep the subject size the same, ie walk closer with the 50mm, you will see that the DOF is the same.

However, to keep the subject the same, one lens, the shorter one (50mm), has to be closer (shorter focal distance) to the object. Since the focal distance affects the DOF, is it not the decreased focal distance that is reducing the DOF to the same level as the longer lens?

 

[Alex_B]

we had a quite heated discussion on this the last two days... have a look here:
http://www.thephotoforum.com/forum/showthread.php?t=123368

but since it ended in some big discussion, it might be a bit confusing

 

[Socrates]

we had a quite heated discussion on this the last two days... have a look here:
http://www.thephotoforum.com/forum/showthread.php?t=123368

but since it ended in some big discussion, it might be a bit confusing

Yes. Why "revisit" a topic that has already been beat to death?

 

[evo5gsr]

Yes. Why "revisit" a topic that has already been beat to death?

So we can beat it up some more.

 

[Joves]

Yes. Why "revisit" a topic that has already been beat to death?

You arent saying this this is

Are you Socrates?