Expression help on focus pull

Hi All,
I’m slowly trying to get my head around expressions and it is slow thats for sure.

I have a locked off shot that has a focus pull that i need to match in a CG element. My theory which is going in the right direction is to do a 2 point track on the plate with so that the scaling value moves as the focus pull occurs. Then take this scaling value say the X value and apply it using an expression to the defocus value. This is sort of working but the value needs to be magnified as the scale value was very small. Can someone tell me how i can make 1 increment of the scale value equal 10 of the blur value. I’m really hoping to nail this as i think it could be a great way to match a pull focus. Be a great matchbox for some to write who is far more clever than me. Many thanks as always Marcus


Aah thank you Andy i shall give it a go. Superstar.

Hi Andy,
Do you know if there is a way to set the values of the scale which is working from 100 to 98 in X so only scaling very slightly from the focus pull track to the parameters of the blur between 0 and 100.

I think i gave a bum steer with my original request as multiplying the scale to the blur *10 is just making my blur sit between 980 and 1000.

So basically i’m looking to make a tiny adjustment of the scale work on a much bigger range on the blur.

Many thanks for your brain power on this. M

Hey @Marcus_M

As far as I understand you’re looking for something like:
Blur: 0 Scale=100
Blur: 50 Scale=99
Blur: 100 Scale=98

If that’s the case your scale expression would be:

100 - (blur / 50)

Or if’you want to create an expression for blur:

(100 - scale ) x 50

It could be adjusted for finer control maybe, but this is more or less it.

Hope this helps

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Thanks Sinan ill go take a look. Really appreciated. M