Focal Length and Depth of Field

[theeyeshaveit]

HI everyone,

I get why aperture can affect DoF, but cant quite get into my head why focal length does.

Can anyone enlighten me (in simple terms!!)

TEHI:bonk:

 

[billybob99]

have a read here

 

[philgale]

i don't know but this might help, had a quick read and seams to make sense

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Beat me too it....

 

[gad-westy]

And when you've read through that, try some numbers in here. A great tool.

 

[AJQS]

On it's own it doesn't, it's all about the size of the subject relative to the frame. The larger you make something in the frame, the shallower the DOF on it will be, ehetehr that's by using a long focal length lens and staying in the same poisition or by uisng a wide angle and getting ridiculously close, for the same aperture the DOF will be the same.

 

[HoppyUK]

As Alan says, focal length does not change DoF by itself. If the subject stays the same size in the frame, either by changing the lens, or distance, or both - DoF stays the same.

However, it's a common misunderstanding that long lenses reduce DoF. What happens is that longer lenses have a narrower field of view, which makes any background behind appear relatively bigger. This simplifies shapes and makes them appear less cluttered and distracting, so the main subject often seems to stand out more in a similar way to shallow DoF.

It can look very much like a depth of field effect, but it's not.