Focal length

[DanHD]

I'm tired of people saying focal length has a direct effect of depth of field. My professor keeps teaching that in my class, and it pisses me off.

it doesn't! it has an indirect effect, in that longer focal lengths increase magnification of the out of focus background areas, while compressing the visual perspective.


My teacher passed out a pamphlet on DOF that says "longer focal lengths create a shallower depth of field"

 

[KKeller]

you should send your teacher this
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

 

[j1clark@ucsd.edu]

I'm tired of people saying focal length has a direct effect of depth of field. My professor keeps teaching that in my class, and it pisses me off.

it doesn't! it has an indirect effect, in that longer focal lengths increase magnification of the out of focus background areas, while compressing the visual perspective.


My teacher passed out a pamphlet on DOF that says "longer focal lengths create a shallower depth of field"

Depth of Field is calculated from the parameters, Focal Length, Aperture, and Circle of Confusion.

The formulas are somewhat complex, but in a venacular way, 'focal length' directly affects the hyper focal distance, which in turn affects the near and far end points of the 'acceptable focus' for a given circle of confusion for distances other than the hyper focal distance...

 

[Barry_Green]

We go through this all the time. While it's technically true that focal length doesn't actually impact the DOF, it certainly looks like it does. When I show you this shot, would any reasonable person say that the DOF is the same? (I mean, whether it is or not, it sure doesn't look like it is!)

The only thing that changed in that shot is the focal length...

 

[morgan_moore]

Depth of Field is calculated from the parameters, Focal Length, Aperture, and Circle of Confusion.

..

and subject distance /framing

shooting with a wide and cropping is not differet to shooting with a tele from the same point (apart from loss of resolution etc)

Filling the whole frame with a wide or filling thewhole frame with a tele at the same aperture will have different DOFs

S

 

[j1clark@ucsd.edu]

We go through this all the time. While it's technically true that focal length doesn't actually impact the DOF, it certainly looks like it does. When I show you this shot, would any reasonable person say that the DOF is the same? (I mean, whether it is or not, it sure doesn't look like it is!)

The only thing that changed in that shot is the focal length...

Changing the focal length changed where the near and far distances of 'acceptable focus" occur... aka DoF...

The other factors affecting 'accpetable focus', are ultimate enlargement, and of course, what is 'acceptable focus'... which is ultimately dependent on circle of confusion...

 

[Barry_Green]

... and circle of confusion size is innately tied to final viewing size, a fact that many people seem to completely misunderstand...

 

[j1clark@ucsd.edu]

... and circle of confusion size is innately tied to final viewing size, a fact that many people seem to completely misunderstand...

Which of course is why I liked my 4x5 contact prints shot at f/22-64... but it's tough to load the view camera at 24 fps...

 

[AwakenedFilms]

4x5 @ 24fps...sounds like scarlet.