All language subtitles for 06_Field_curvature

in this lesson

we're gonna learn about field curvature

which is a somewhat rare optical problem

but we still need to know about it

and we can still apply it

so here's where we left off

and I've added some notes to our lens distortion

as you can see here

whether you are adding it to a CG image

or using it inside of a real footage pipeline okay

so now let's talk about field distortion

and this is an image essentially describing

uh field curvature distortion

so what happens is

uh we have these circular lens elements

and so when we focus on a specific area

or when the center

light focuses on a specific area

the light that comes in from an angle

wants to focus on a curve or a circle

now if you think about the inside of your eye

this is exactly what's happening

we have our Iris in the front

and it is hitting this curved backing

so that we can focus

uh essentially across our entire field of vision

now in the real world or in our cameras

we have a flat sensor

so what happens is that this

field curvature means that objects

or light that is coming in

not from the center

but from the edges of our lenses

will begin to be blurred

and as you can see here

the focus is actually in front of the sensor

so when the light hits back here

we are going to have a blurry object

so what this says is

inside of any frame

the edges of our frame should be slightly blurred

now in the real world

camera lens manufacturers again

are very smart people

and they have figured out how to manufacture lenses

so that this blue light

actually focuses very close to the initial sensor

however it is not perfect and we

can learn how to add this in so again

field curvature

is something that happens in the real world but

many lens manufacturers have spent a great deal of time

fixing this but again

let's add in just a little bit okay

so the question is

how do we blur just the edges

now you might be thinking

let's add in a roto node and let's add in a blur node

uh kind of like how we created our vignette

and that will not actually work uh

how we want

the Blur Mask port will only

mix between blurred areas and not blurred areas

so instead of connecting this up

let's just throw that out entirely

so what we're looking for is a note that will blur

different amounts based off of image data

and we actually have one of those

it's called the Z Blur note

now uh it's gonna be at the bottom of my list

so I'm gonna hit tab and drop in a Z blur

and this is traditionally used to do

depth blurs however

what we can do with this is also use it to

blur different parts of our image at different values

okay so let's plug this in

and initially

this is gonna be going off of a depth channel

which we honestly don't have yet

as you can see here

it is empty

and so it is just blurring our entire image

now for this

we're gonna need a

some kind of an image that shows us where

the corners are

and if you're feeling

uh really creative

or if you remember earlier

we could use this

radial that we created to um

add in our vineyarding

so let's go up here

and let's see

do we want to

pipe it in uh

let's just shuffle

copy this into a new

channel for now

so when I hit tab

and let's type in the shuffle copy note

and I'mma plug this in

to our current pipe

and plug this into our radio

and I'll add a note here so we

remember what we're doing

so this is going to be copy

in vignette

okay so we'll take the alpha

of R1 which yep

and let's plug this into a new channel here

so let's go to

new channel

it's gonna call this our vignette

and we don't really need RGB

uh so we'll just

call this the alpha

and let's plug the

red into that vignette

so now if we go to our vignette channel

we have this nice

colour okay

uh if you wanna learn more about shuffle

copy or channels in general

take a look at our introduction to channels

in nuke course

alright so back to our Z blur

so now let's take a look

and down here

we still have

our vignette channel

because every single merge is going along the B pipe

and let's see here

it looks like oops

this Z blur is

not going through

our last lens distortion

there we go

okay so now

let's change

our Z channel to

our vignette dot alpha

and here we go

everything comes back into

sharp focus

and let's go to

our focal plane set up

and let's begin

changing our focal plane

so what we wanna do is

we wanna have the entire

center area green

so let's pull

the focal plane back a little bit

and let's increase our

depth of field

quite a bit

let's give it a second here to think

so let's keep pulling this focal plane back until we

get into the center of our image

okay great this is looking much better

okay so now

anywhere in green

we will not

be blurring

anywhere in red

we will be blurring

so let's take a look

at this now

and we can see

it's a very

subtle effect

but you'll notice

now our edges

are the edges of

our frame are

ever so slightly blurred

and again this is

uh partially

or we're adding this to

show field curvature

now our current settings of a level 1 blur

or a size 1 is probably pretty good

again most lenses

will not show too much field

curvature in them

but if you want to really uh

blow this out

you can continue to increase the size

so that well

maybe not that much

that's a little extreme

but as the objects get closer

and closer to the

edge of our frame

they begin getting more

and more blurred

and of course

you can come in

and play with this focal plane setup

maybe decrease the

depth field a little bit

um maybe pull

forward the focal frame

or the focal plane

so that only the center

is in focus

and as you can see

that just adds a little

bit to our image

now this is a little bit too strong for my taste

so let's come back here and let's reduce the size

and again increase that depth of field

until we are only blurring the edges of our image

okay great so now we've come in

we've added just a little bit of field curvature blur

so that the edges are much more

or a little blurred compared to the center of our frame

and this gives us uh

somewhat similar to a vignette effect

in that it makes us

makes us focus on the center of our frame

so that is how we can add in a fuel curvature blur

effect here inside of nuke