# f stop

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### #1 jkunz07

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Posted 25 April 2012 - 07:03 AM

Hey, I'm trying to figure out what kind of math is being done when calculating the f stop for depth of field.

Reading the docs here, it states that "There are four parameters that control depth of field. The Focal Length parameter is on the View tab of the camera node. The Focus Distance, F-Stop, and Bokeh parameters are on the Sampling tab of the camera node."

To better visualize depth of filed I'd like to create planes to get a better idea of how narrow or wide the effect will be, I have a scene with a focal length plane, and a focus distance plane.  I'm just not sure what type of calculations I should be doing to place the f stop planes (near and far).

Any help on this or ideas to try would be great, Thanks!
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### #2 anim

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Posted 25 April 2012 - 10:36 AM

while looking at your scene outside of the camera, select camera, press enter to get its handle, press Z to get focus handle
now you can set your focus plane and dof range interactively in viewport
Tomas Slancik
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### #3 jkunz07

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Posted 25 April 2012 - 01:17 PM

anim, on 25 April 2012 - 10:36 AM, said:

while looking at your scene outside of the camera, select camera, press enter to get its handle, press Z to get focus handle
now you can set your focus plane and dof range interactively in viewport

Thanks, I didn't know about the z key, it's starting to make more sense now.

I'd still be curious about an equation to derive f-stop planes given an f-stop value, focus distance, and focal length.  I'd like to be able to create some ramps based on these parameters so I could apply it to particles or volumes.

From playing around with the range and observing in the viewport it looks like there's some type of exponential decay being applied to the f-stop planes as f-stop increases,  I might be able to replicate through trial and error comparisons, but if anyone could help me out it'd be appreciated.

Thanks!
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### #4 vectorblur

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Posted 01 May 2012 - 07:20 AM

You might want to study relationships / equations used in physical optical systems.

Check the following link with Dof Calculator as a bonus!!

http://www.dof.pcraft.com/dof.cgi

Cheers,
Eh *munch munch* what sop, doc?

### #5 jkunz07

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Posted 08 May 2012 - 01:04 PM

vectorblur, on 01 May 2012 - 07:20 AM, said:

You might want to study relationships / equations used in physical optical systems.

Check the following link with Dof Calculator as a bonus!!

http://www.dof.pcraft.com/dof.cgi

Cheers,
Thanks, I've been pretty busy recently but I've managed to make some progress on figuring out the equation.

I attached a file with the expressions on a null node.  Some locaters are hooked up to vis the near DOF and far DOF.

If anyone wants to give me some tips/feedback it'd be very useful.

Thanks for everyones help so far.

#### Attached Files

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