Physical Camera. Still vs Movie

[Metzger]

Is it normal to have the render get blown out when switching from Still to Movie?

Using a Domelight with HDR texture @ version linux_x64_13829


Thanks

[mr furious]

I had the same thing happen, I thought is was because I don't really know what the differences between getting an exposure on a "movie" camera versus a "still" camera. I just switched back to still because that's what i understand a bit better.



A

[pechart]

Same thing happens here everytime we switch to the movie camera. I think the difference is, that in the movie cam the shutter speed is ignored because the shutter method used in filmcameras is simulated. The shutter speed is determined by the framerate and the shutterangle. The shutter opens and closes simply once per frame and this results in a brighter image.

[Metzger]

Yeah but when using still camera, you don't get the same results with motion blur. Motion camera really calls for adjusting your lighting drastically. I wanted to make sure by Vlado that this is correct and not a bug.

What I love the most out of the physical camera is getting properly defocused reflections from reflective surfaces. It really makes all the difference. If I remember correctly, the DOF in the Vray render settings do not calculate the same.

[bernhard]

Hi,

the movie cam acts like a real movie cam, so far I couldn't find any bug.
Of course, when you setup your scene with a still camera, and you switch to the movie cam it will not expose the same way - simple, because when switching to the movie cam, you just start with some standard settings.

But don't worry about that, that's totally fine.

Motion camera really calls for adjusting your lighting drastically

No. Actually not at all. You should not touch your lighting, when you know your setup is correct. You should adjust your movie cam.
You can control it like a real movie cam, that's really fantastic.

You also mentioned motion blur. Yes, of course you get also a different motion blur - but that's how it is, that's how the movie cam works.
For animation, I prefer to use movie cams only, because you can control all things you need ... motion blur and exposure and it just keeps things simple.

This will help you understanding:
http://en.wikipedia.org/wiki/File:Mo..._animation.gif


You will see, after using the movie cam for animation, you don't want to pick the still cam anymore.

Happy rendering !

[Metzger]

bernhard: I would love to see a test scene. Matching film motionblur using a non physical camera I would get matching results at 180 camera shutter with a duration fo .5 and interval center at 0. When I set a physical motion camera to 180 at 5.6 aperture I am blinded. Do I need to start building tents and block out light from outside windows in my 3D? hehehe

[djx]

I'm interested too. I've been simply lowering the ISO number to reduce the exposure. It gets the job done but the numbers required just seem a bit odd.

[bernhard]

yeah .. I am in the middle of a relocation, but when things are settled I'll be back, roughly scheduled in about three weeks... then we can work on a sample scene..... but what I do understand from your request... it sounds that you try to match exposure and motion blur by sticking to some specific values, like an 180 angle ... that all doesn't matter... or if I do understand your right, this is not built for that.... you simple set the settings of your movie cam, that you get what you want to achieve: what means, the right exposure, as well as the right motion blur.

I never stick to values like an angle of 180 or anything else.... and I think this explains now.. you shouldn't stick to some specific values you mentioned above.... you should just simple adjust the movie cam.
like mentioned earlier, when my relocation process is done... I'll come back to you with that topic....
so far so good,
happy rendering

[djx]

You seem to be saying that the values are just arbitrary. That is what sounds strange to me. I would have expected a physical camera to use values and methods that would match as closely as possible the real world. I realize that other factors in maya probably make this impossible to be 100% accurate, but I would hope that choosing a shutter angle would give me roughly the motion blur I see in a real camera, and that combined with apperture and ISO would approximate the type of exposure (especially when using other physical stuff like sun and sky or photometric lighting).

[Peter Grealy]

Hi All,

I've done a little bit of recon to try and de-mystify Movie Camera mechanics so I too can try and replicate real world values. In the film industry there is a "180degree" rule that your exposure setting should be double your frame rate. Eg, If you are shooting at 24fps your exposure should be 1/48 of a second (Shutter Angle @180degrees) This link helps explain it in more detail http://blog.tylerginter.com/?p=385 Then all you have to do is expose the image correctly by adjusting the film ISO or aperture and you get the perfect shot right/correct motion blur. The problem with trying to re-create this in Maya is that the Vray Movie Camera does not take into account Shutter Speed. The shutter speed has no effect at all when using "Movie" camera so trying to get a real world result is a null argument-please correct me if I'm wrong. I think the end question should be is how much motion blur do you want artistically. Simply use the Shutter angle to control how much motion blur you want and use the ISO of F/Stop Aperture to expose the image correctly. A shutter angle of 1degree basically has zero motion blur and a shutter angle of 360 has maximum blur (Anything above 180 is mechanically impossible in the real world anyway).

[Metzger]

The physical camera is not complete for motion camera. The missing variable in the equation is frames per second. Because 24fps at 180 degree any one frame is exposed at one 48th of a second. If my footage is filmed at 96 frames per second, then I have no way to adjust correctly when I need my maya scene to stay at 24fps.

If I was 96fps at 180shutter then the 1 frame exposure time is 1/192 of a second, but there is no proper correlation of shutter anagle on film camera for exposure time and still camera that has exposure time.

So we need frames per second control. And the test would be something like:

Still Camera
Film Gate: (35mm)
ISO: 100
F-number: 4.5
Shutter Speed: 48 (1/48 sec)

Movie Camera:
Film Gate: (35mm)
ISO: 100
F-number: 4.5
Shutter Angle: 180
Frame Rate: 24fps

The to camera should produce the same image

[Peter Grealy]

A 'frames per second' control per camera would be nice. And / Or a checkbox to match/use Maya's preference setting for FPS. Has anyone tried to match vray's motion blur to film motion blur in a production environment?

[Metzger]

Having an option to default with Maya's Preferences but I wouldn't make it the default. I have matched non-physical camera motion blur setting camera to 180, then motion blur set to duration of .5 and interval center at 0. That matched my plate perfectly.

[Metzger]

I tried a newer nightly build and notice that there is still no option to specify fps for the physical motion camera. If you use the physical camera motion camera to match something that is timewarped, you can't correctly do this.

Reason is this. I might have something that was originally shot at 96fps, but the new plate that is timewarped will go between 96fps-24fps. But what matters is that I can set the camera to 96fps even though I have a scene set to 24fps.