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Exposure value in Color Management should not be limited to 20 stops.
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System Information
Windows 10 - GTX Titan X - i7 3930k

Blender Version
Broken: 2.79.4 nightly build

Short description of error
The Exposure value under Color Management has a limited range from -10 to 10, which is not enough to cover the large range of photographic exposure. I suggest to use -10, 10 as soft_min and soft_max for the slider, but not as hard min and max. Users should be able to input values outside of this range if needed.
I am making/using the Photographer add-on to control the exposure of my scenes using photographic exposure settings, and there are cases where the add-on would not be able to set the proper exposure value because of this limited range.

Event Timeline

I've increased the range now because it can be useful in some cases, but I would advise against setting up lighting so that it requires such small/large exposure. You'll get really poor float precision in rendering and compositing.

Unlike in the real world, in rendering the time the shutter is open does not control the brightness of images, it only controls the amount of motion blur. I can see it would be useful to be able to control settings as on a real camera, but this does not require the actual render and compositing to be performed with very small/large values.

Fair point. I will be using EV 8 as the exposure 0 in Blender as it should be a good default for most lighting scenarios.
In the long run, instead of using the Exposure viewport transform, what about pre-exposing the render with the camera settings? It won't be updating in realtime unfortunately, but then you could make sure to maximize precision without having to change all lights intensities? Is that maybe what the Film Exposure is for?

Thanks a lot for the very quick fix, happy to have you back at the Foundation :)

I don't think pre-exposing the render would help precision. It's not clear to me how you get to values that need exposure outside -10 to 10 in typical cases, normally when you set aperture and shutter speed on a camera it's done in a way that they mostly cancel out, so the resulting exposure value in Blender would be relatively small.

If done correctly, one should not need to go outside of this range to get a properly exposed image. However, to make sure that my HDRi has all the range for instance, I sometimes want to push the EV up to 25, 26.
And then there is also the fact that people may change camera settings to weird settings, and not see any exposure change happen, and will think it's broken. I think it's better to have it always work, even if it's wrong settings.
I agree with that -10, 10 range, that why I think they should stay like this as soft_min and soft_max of the slider :)