I’m trying to model a propeller and in doing so I want to have a motion blur to show velocity. In Blender, there is an option for sampled motion blur, but I’m finding that I need in excess of 20 samples for it to look right (see attached .blend)
I have tried looking at vector blurring, however that does not accurately capture the motion at all for fast-rotating objects (the object rotates so fast that its frequency gets aliased). The specific project I’m working on takes about 1 minute for each “sampled motion” blur, resulting in each frame taking in excess of 20 minutes (and there’s 600 frames to go).
Since I only really need the sampled motion blur on a single object, is there a way to isolate the sampled motion blur to that one object, or am I stuck with having to do the whole thing?
kev717 you mentioned samples in motion so are you by any chance in Blender Internal. And, if so why is one frame taking 20 minutes. Oh, twenty (20) samples. It’s been awhile since I used BI but if I’m not mistaken the Blender Guru on his three thousand dollar machine couldn’t use twenty samples.
I don’t recall what a obscene number would be there but play with the shutter speed and then maybe up the samples by several. More trial and error and then maybe several more samples. I suspect you might be on a laptop but even at that a 20 minute frame in BI would render a walk through of the Sistine Chapel. If this comment came off a bit flippant that wasn’t the intent. Us folks on modest machines have to stick together.
It’s just with animation it’s what we would like to have and then what our equipment is capable of. I see you are no newbie but I have no way of knowing when you developed a interest in animation. One compromise almost all of us make is to use 720p by the way. If I have time I would love to view your blend file although I’m no master in the animation field. BI is extremely fast unless you load it down with some generous settings in transparency and reflections. Damn the question: You are stuck with motion blur for everything I believe.
The particular scene I’m rendering has about 800 particles active at any given time, transparency, mirrors, and a copious amount of raytracing. That’s why it’s taking 20 minutes (well, 1 minute for each pass of the sampled motion blur). The rest of the image looks fine with the vector blur effect, but the propellors look terrible.
Yeah, always remember Alfred Hitchcock’s acting advice to Ingrid Bergman:
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“Fake it, Ingrid.”
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A spinning propeller is not worth accurately simulating. Maybe show the props starting to turn, then cut-away to something else and when you return the props are at full speed. But they're not props anymore, and no one will ever know or care except you.
Motion blur is very expensive to begin with, far more so because Blender will re-recalculate the intermediate frames every single time. Therefore, use any other kind of blur, e.g. vector blur or simply blur. Arrange the shots and the editing so that the viewer’s eye will never be drawn to this part of the shot “for critical review,” but will simply understand what s/he is seeing, visually remember what s/he previously saw, and pay it no further mind.
If you want to simulate the effect caused by film shutter-speed while photographing a rapidly spinning object, use two wheels, one rotating slowly backward.
As one who likes to make things accurately as possible, I can understand your desire. What I would try is to create a secondary scene and link all the necessary objects to it (camera, lights, propeller) just enough to get the look of the propeller decent, then go back to the original scene, the node editor, compositing nodes, and add in your secondary scene and an “alpha over” node. When you render your scene it will render both scenes separately and then merge them together. Because the scenes have linked objects editing the one should reflect the changes on the other.
UPDATE: I did a quick test with this idea, and it “works” after linking the object to the new scene I recommend moving it to a different layer in the original scene. My test was two cubes, moving in a straight line. The issue I noticed was that both types of blurs seemed to be timed differently. If I render both together with the same blur type they looked like they were pretty much travelling in parallel. If I isolated one of them and set it to a different blur type with the same settings (0.5 frame for example) one looks as if it’s moving faster than the other and is slightly ahead of the other.
It seemed like the sampled motion blur begins at the point of the frame and continues to the 0.5 frames toward the next frame. The vector blur seems to start 0.25 before the current frame and continues to 0.25 towards the next frame. This was very noticeable in the single frame, with motion and with other elements it may not be a noticeable at all.
Also, if you want to . . . “give 'em a good, close look at the propeller spinning-up.” Then, cut away and fuhgeddaboudit. Having once seen it, the audience will “see it” thereafter, even if it’s not actually there. As long as what they do see is not “jarringly different,” they will pay no mind to the propellers anyway. (They’ll be looking for the Red Baron in the clouds . . .)
There is a “return on investment (ROI)” to be considered in visual effects, because “you want to get the damn thing finished!!” :yes: If there is a cheaper and faster way to do it “almost as well,” do it that way, so that you can spend the computer’s time more profitably on other things.
Star Wars Episode Oneshipped to theaters with a “podracer race audience” that consisted of colored Q-Tips cotton swabs! The trick was un-noticed by theater audiences until pointed-out in a “Making Of” video. (The shot was replaced on the DVD.) Once the audience had seen a close-up of the audience in a prior shot, they continued to “see” the same thing thereafter. Movies are (still) full of tricks and short-cuts like this. You agonize over the shots frame-by-frame in the process of “cutting it,” but your audiences do not.