Motion blur defaults to 360° shutter?

[LudvikKoutny]

Hi,

I am quite curious about why when enabling motion blur in render settings, MB duration defaults to 1.0 frames, which mean 360° AKA shutter crime. 360 degree shutter usually produces ugly smeary MB and therefore is often advised to be avoided.

So right now, I am not sure if it's really this weird default value, or if I misunderstood how MB duration value works (like some conversion going in behind the scene and therefore 1.0 meaning 180° shutter).

Thanks in advance.

[Slazzo]

I usually thought, if my frame rate is 24/s, 1 frame interval must be equivalent 360°, but in V-Ray I've also noticed the time domain is sampled more to the end than uniform over the time domain,
please someone from Chaos correct me if I'm wrong, is the time domain samples time = pow(random[0,1], 0.5) ?

[LudvikKoutny]

I usually thought, if my frame rate is 24/s, 1 frame interval must be equivalent 360°, but in V-Ray I've also noticed the time domain is sampled more to the end than uniform over the time domain,
please someone from Chaos correct me if I'm wrong, is the time domain samples time = pow(random[0,1], 0.5) ?

I think that's due to the internal center being set to 0.5 by default, meaning the sampled segment is being shifted half way between current and next frame, where as value of 0.0 is the one where sampled segment will be in the center of current frame.

But i am still mainly intersted if and/or why it defaults to 360° shutter.

[LudvikKoutny]

For some reason i can't edit my posts... anyway, i meant interval center, not internal

[vlado]

There is no specific reasoning behind this. From what I remember in a previous discussion on that topic, most people would have preferred the settings to be duration 0.5 and interval center 0.0. While I generally agree about the duration, the center value is a bit more problematic - many geometric primitives in 3ds Max change vertex counts on a frame boundary, including realflow caches etc. which would prevent V-Ray from generating motion blur in that case. Of course, strictly speaking, this is not a V-Ray problem, so we might as well change the defaults...

Best regards,
Vlado

[LudvikKoutny]

I actually have no problem with interval center. Just the duration. Sometimes i just turn on motion blur, and from other renderers i am used to 180° shutter. Then once i render preview, its not always obvious shutter angle is too high, so i may miss it and find out the nasty surprise only when the entire animation is done rendering and something looks odd.