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View Full Version : Motion blur on propeller VS rest of plane.



mrpapabeis
08-25-2008, 12:47 PM
How do i get motion blur on just the propeller of a plane and not on the plane itself?

Should I use two cameras parented to a null, and rendered in two seperate passes?

Render the props on a seperate pass?


Use another as yet to be discovered killer method?

Giacomo99
08-25-2008, 01:03 PM
All those would work. You could also try rendering the spinning propellor head-on and applying it as a transparency map to a (flat) cylinder primitive.

Andrew March
08-25-2008, 01:05 PM
If it's just a still image then position the plane as you want it as a static object and just rotate the prop as normal, I've attached an image as an example.

mrpapabeis
08-25-2008, 01:32 PM
Great idea but the plane is moving, hence the problem.

rwhunt99
08-25-2008, 03:22 PM
you didn't say if this was a single render , or an animation. for an animation one way would be to parent a camera to the plane so it won't show the motion blur move of the aircraft.

The position of the camera makes a difference > plane traveling across the frame will be extremely blurred while if the plane is coming towards or away from the camera > less blurred. It deends on how much movement between frames.

If you use a post process application, you can leave off MB and do it in post.

shrox
08-25-2008, 04:08 PM
If the plane's path was set to stepped, would that solve the plane motion problem?

mrpapabeis
08-26-2008, 02:36 PM
Sorry guys. I'll be a bit clearer. This is a composite shot with a live BG, 9 Secs long.
Plane banks in from far away, the comes in straight for the camera flying low. I tweak the blur for the props till it looks good, and of course the blur on the body gets pretty extreme. I've got the props spinning at 10,000 rpm. To get a nice blur on the props I have to set it at @ 600%. I could set the rotation of the props at perhaps double (20,000 rpm ) and lower the blur. See what that does....

ivanze
08-26-2008, 03:30 PM
This plugin form worley does what you need:

http://worley.com/E/Products/polk/clay.html

Read ObjBlur.

But I remember there was a free one in flay that does that too, but I can't remember the name.

Captain Obvious
08-26-2008, 05:24 PM
It's really quite simple: Set it up as you would in real life!

If the camera is moving the same direction as the plane (so that the plane itself is stationary in the frame), the plane itself will not be blurred. If it's for an animation, a plane moving through the frame of a camera that is stationary WILL be blurred and it will look bad if it isn't.

Another technique you can use is to spin the propeller faster. If you up the rotational speed by a factor of ten, and decrease the shutter time by the same factor, the amount of blur on the propeller will remain the same but all other motion blur will be significantly reduced.

virtualcomposer
08-27-2008, 09:58 AM
if it's just a picture, keep the plane stopped and move only the propeller. It can't have motion blur if it isn't moving.

Nangleator
08-27-2008, 02:49 PM
Dude, 10,000 rpm?! 2,600 rpm is about the highest a civilian prop plane turns. Warbirds might push that a bit, but there's little point in spinning those tips much past the speed of sound.

On cruise, you might be turning 2,000 to 2,400. Final landing approach, 1,200 to 1,500 rpm.

For LW purposes, you may get by spinning far slower.

cagey5
08-27-2008, 02:50 PM
if it's just a picture, keep the plane stopped and move only the propeller. It can't have motion blur if it isn't moving.

I think you'll find that's been suggested before and answered before.

tribbles
08-27-2008, 05:37 PM
I'd do what the good Captain said: Another technique you can use is to spin the propeller faster. If you up the rotational speed by a factor of ten, and decrease the shutter time by the same factor, the amount of blur on the propeller will remain the same but all other motion blur will be significantly reduced.

(I was writing something just like that, but thought to check in case someone else had mentioned it!)