V-Ray 5.00.01 Exposure Settings / Issue

[andy_smith]

I'm wondering if there's a bug in V-Ray 5.00.01 for Sketchup:

We have the EV (Exposure Value) setting under the Camera rollout. When you move that slider, the values under the Advanced Camera Parameters rollout change (Film Sensitivity and Shutter Speed).

When I increase the EV number to increase the exposure/brightness of the render, I would expect to see the Shutter Speed decrease (longer exposure) and the Sensitivity to remain constant: In real life, ISO increases noise/grain and is potentially undesirable - I am not sure if its inclusion in V-Ray is for the familiarity of photographers, or whether its intent is to allow you to add noise while increasing brightness/exposure. Either way, it should be possible to keep the Aperture constant, the ISO constant, and use Shutter Speed to alter the exposure.

Furthermore, the Shutter Speed is expressed as 1/s and has values from -1000000000 to 1000000000. This would indicate that one end of the scale is many hours and the other is extremely short length of time. However, assuming that 1/1000000000s is very fast (a billionth of a second), then the image should be very dark, assuming an aperture of 8 and an ISO of 100. Conversely, 1/-1000000000 is at the other end of the scale and could be assumed to be very slow (ie a long time) and the image should be brighter.

In V-Ray 5.00.01 if I keep the ISO at 100 and the aperture at 8 and slide the Shutter Speed slider, I get the following:

Shutter Speed 0 = EV has no value/number and the image is black. OK, so this implies that 1/0s is with the lens cap on or something...
Shutter Speed 1 = EV jumps to 6 and the image is somewhat bright somewhat dim. So this is a 1 second exposure.
Shutter Speed 500 = EV 14.966 and the image is duller. You'd expect this because this is a 1/500s exposure.

So Shutter Speed 1000000000 is a billionth of a second and is pitch black as you'd expect.

But how do I do a 2 second exposure, or a 10 second exposure?

-1 does very odd things to the HDRi in the Dome Light and seems to make the render give up with the scene full of noise and artifacts. Going further into the negative (say, -1000) yields a black image. So what's the point of the Shutter Speeds from 0 to -1000000000?

Or am I just misunderstanding how the camera settings are supposed to work in V-Ray?

[konstantin_chaos]

Hi,

Shutter speed of 0 or a negative value is actually invalid.

You should calculate the Shutter speed as follows:
shutterSpeed = 1 / seconds

...
0.2 seconds exposure = 1 / 0.2 = 5
0.5 seconds exposure = 1 / 0.5 = 2
1.0 seconds exposure = 1 / 1.0 = 1
2.0 seconds exposure = 1 / 2.0 = 0.5
4.0 seconds exposure = 1 / 4.0 = 0.25
10 seconds exposure = 1 / 10 = 0.1
etc.

And the reason why we only change the ISO when you move the EV slider is to avoid Depth Of Field and Motion Blur from changing.
The F Number affects DOF while the Shutter Speed affects Motion Blur...
And since in V-Ray big ISO values don't cause artifacts this is the best way to do it.

I also think it's a mistake that the slider is not limited to 0.

Hope that helps,
Konstantin

[konstantin_chaos]

Hi andy_smith,

Negative Shutter Speed values will no longer be allowed in the next version we put out.
Thanks for bringing my attention to this.

Konstantin