[guerillary]

I'm setting ISO & rotary shutter values in the Maxwell for Maya plugin settings however different values are appearing in the render module's readout. Can you please explain why those values are different? Is the bug just a typo or is Maxwell ignoring the plugin values? Thanks.

[Mihnea Balta]

The only exposure controls natively supported by Maxwell are ISO, f/stop and shutter speed. The rotary shutter feature works by replacing the shutter speed with the value computed from the shutter angle, then adjusting the ISO so that the exposure matches what would be obtained by using the original ISO and speed. The priority controls work in a similar manner. We can't store the shutter angle, EV number or exposure mode in the MXS file. When you open the MXS in Studio or Maxwell, you see the adjusted values.

[guerillary]

Thanks for the reply but I'm still a little confused.

I am entering an ISO of 320 and rotary shutter of 180 in the Maxwell for Maya plugin camera attributes; in the "Maxwell Settings" of such camera attributes.

When I render a frame, the ISO shows up at approximately 50 and the shutter displays as 1/48.

Does this mean Maxwell's Maya plugin isn't passing the settings to the Maxwell renderer?

[Mihnea Balta]

It's not passing the settings as you entered them, because you wouldn't get the exposure you want.

You probably have a shutter speed value around 1/300 set in the camera attributes. When rotary shutter is enabled, that shutter speed can't be used directly, because the shutter angle defines the shutter speed. In your case, an angle of 180 degress means the shutter stays open for half the frame, so, at 24 fps, the shutter speed will be 1/48 seconds.

The plug-in then adjusts the ISO so that the render with speed 1/48 has the same exposure you would see from shutter speed 1/300 and ISO 320. If it didn't perform this adjustment (leaving the ISO at 320), varying the shutter angle would also change the exposure: an angle value of 180 degrees would produce images twice brighter than at 90 degrees. The angle setting is meant to give you a way to control the length of the motion blur trails, and it's better to be able to do that without affecting the exposure. It's the same principle as with the priority modes on a standard DSLR (and on the Maxwell camera): control the DOF or motion blur while keeping the exposure fixed.

[guerillary]

Thanks for the reply. So the render module needs to calculate in a different fashion to work properly while maintaining a proportional relationship to my settings.

[guerillary]

Actually, can you please explain your last reply based on my scene information below...


Maya Scene Camera, Maxwell Render Controls:

Manual Exposure Mode
Shutter Speed 750
F-Stop 5.6
Film ISO 400
Using Rotary Shutter of 180 degrees


Maxwell Render Camera Settings (for above scene passed from Maya plugin):

Camera ISO 25.6
1/Shutter 48


Thanks.

[Mihnea Balta]

As above, a shutter angle of 180 degrees exposes the film for half a frame (the shutter rotates 360 degrees per frame, so you have 180/360). A frame is 1/24 seconds, therefore the shutter speed will be 1/48. This overrides the value you entered (you can't have both, because they represent the same thing; film cameras don't have shutter speed controls, only shutter angle).

The shutter speed entered by you is 1/750, which is 15.625 times smaller than what comes out of the rotary shutter computation (750/48). Therefore, to obtain the same exposure as with speed 1/750 and ISO 400, the ISO is divided by this proportion. 400 / 15.625 = 25.6.

You can check that this works by rendering once with rotary shutter disabled, then with it enabled. The two images will have the same exposure. In the first render you will see the parameters you specified for the "still camera" simulation (1/750, 400), while the second render will use the adjusted values. If you have moving objects and motion blur enabled, you will see that the motion blur trails are much longer in the second render (if you don't have motion blur, there's no point in using the rotary shutter). If you change the shutter angle and re-render, the length of the motion blur trails will change, but you will still get the same exposure.