velocity phrasing

[Darby Edelen]

Depending on how you’re doing your ‘zooms’ the answer will be slightly different. If you’re just scaling a photo up then something like:

start = transform.scale; //starting scale percentage
rate = 1; //percent to scale up per second

rate = [rate, rate];
rate * time + start;

for your scale property would work, this would scale the image up by 1% per second beginning at whatever the scale property for the layer is set at. It’s simple but it works.

If you’re using a camera you’d want to apply a similar expression to the zoom property.

[Filip Vandueren]

The funny things with zooms is that if you scale up linearly, it doesn’t feel right, the ‘closer’ or bigger the the layer gets, the slower the scaling happens.
This phenomenon occurs both with scaling layers, and zooming cameras.

(After Effects has an Keyframe Assistant called “exponential scale” to counter this)

If you have a camera and the images come at you with a constant velocity in Z-depth: that does look right because it’s what our eyes know best.
So if your layers are 3D, you could indeed just space the photos in 3D space and move the camera forward or move all the pictures using something like:

rate = 20;
value - [0,0,rate]*time;

(negative Z is towards the camera: so we use – for the pictures, use + to move the camera towards your pictures, assuming ofcourse that the camera is still in it’s default position and not looking up at “pictures on the ceiling”)

if you do want to use scaling it’s easy enough: you just use a logarithmic value instead, this is accomplished by having a ‘power of’ multiplier:

rate=1;
value * Math.pow(2,time*rate);

Use the rate to determine the speed of growth using this knowledge:

After 1 second, the layer will have grown 200%, for rate=2, that will be 2 seconds.

Of course, it might be bes to link all the values to a slider on a Null, so you can indeed just set 1 value to affect the speed of all your zooms.
find out how in Aharon’s Podcast:
https://cowcast.creativecow.net/after_effects/episodes/Expr_Controls_Pt3_POD_AENY.mp4