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I'm moving something fairly fast with a shutter speed of 1/750 (it didn't start out as an animation but even though it's a print job motion blur is now requested) and I'm getting a countable number of afterimages in the motionblur.

I have my substeps currently at 500 which should completely remove this issue, but there they are.

"Motion only" notion blur. No camera motion. Pinhole lens. v3

Any ideas?

Edit:

maybe Maya isn't passing substeps along and they are remaining at default

I thought I could check the substeps in Studio or overwrite them but I can't find the setting anywhere.

Okay, I reworked it so that shutter times would be more like a movie camera and it looks fine.

I guess those substeps get distributed across the time between frames, not across the exposure time no matter how short.

500 is a fantastic overkill for such a motionblur, and especially if it's moving in a straight line, 2 would have been enough.

Mihai wrote:500 is a fantastic overkill for such a motionblur, and especially if it's moving in a straight line, 2 would have been enough.

That's right except that fantastic overkill was insufficient. So was the default 10. So I'm not sure how going to 2 would improve matters.

I don't think Maya even passed along the 500.

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Anyway, slowing the shutter and reworking the image a bit seemed to solve it...

He just wanted to see a bit of motion blur, so the ship is slower, too.



(The text notes are for a client)

Also, while I'm here...

Why does my invisible-to-camera tail fire emitter show up in the alpha when I motion blur?

Is this expected behavior? (I haven't test this issue)

I don't think it was an export issue, but most likely a precision issue. Your shutter time is 0.0013 seconds. With 10 motion steps, they will be about 14 milliseconds seconds apart, which is a pretty small interval, so you might start seeing artifacts due to numerical precision limitations. Going to 500 steps is going to make matters much worse - now the interval between steps is 0.0026 milliseconds, so the resulting positions will surely contain rounding errors. In general, if you have linear movement, increasing the number of steps will never improve the resulting image, but can actually make it worse if the shutter time is small.

The alpha issue might be an engine problem, I'll let Mihai discuss it with the core guys.

Ok, good to know.

I'm in the middle of delivering some stuff so I haven't tested the alpha issue, but it looks like something is wrong there.

This is for print, and I have found the case with print is usually that they want an illustrator's 'idea' of motion blur, not actual motion blur, and it was the case here as well, so that's what I'm doing. Clear image with a few speed lines.

I can confirm this is a bug with MB on, the hidden to camera will not work. Wow.

You can work around this bug for the time being by using the invisible emitter technique: add a bsdf to the emitter, set it to trans 255 and ND1. This will make it invisible in the scene, no matter if the object has hidden to camera on or off, but it will still influence the lighting in the scene.

Thanks.

And that's a good bug to find.

re. MB, I'm using 1/96 s shutter speed (90 degrees mb @24fps) for this very silly render, and for that the maximum substeps before the afterimages became obvious was 7, which is also JUST! good enough for when the wheels are spinning up...

But what if the client say were to ask for a faster shutter with less MB? Could I change the project FPS setting as a workaround? assuming I dont want to go below 7 substeps.



Loving the speedy renders with the new MB btw, thanks NL.

You could also not use the rotary shutter feature at all if you don't want a "traditional" shutter angle for a film look. So just use the shutter speed to change the MB look, and raising the ISO to compensate the light loss with a shorter SS.