Let's now set up exposure controls on our camera. Exposure controls are a relatively new addition to Mental Ray. They let you control the brightness, gamma, contrast, vignetting, and white balance among other things. Rather than tweak lights and shaders all the time, you can create varying exposures or alterations to the images all from one page of options (See Image Exposure1).
It's as easy to set up as selecting from the viewport menu - View > Camera Attribute Editor... then scroll down and find the Mental Ray dropdown. In there are 3 shaders we can apply to our camera. The one we want to play with now is the Lens shader. Click on the icon to the right and select mia_exposure_photographic1 from the list.
Inside of the photographic exposure controls (See Image Exposure2) there are a wealth of options that might not all be clear immediately but will be explained as we use them during the course of the series. The ones we need to concentrate on now are these:
• Camera Shutter - Essentially controls the brightness of the scene. Lower values mean brighter images.
• Vignetting - Adds a darker border to mainly the corners of the image, mimicking the real camera effect. Adds realism.
• Whitepoint - For now we leave it on white, but this will modify the white balance of the scene, letting us control warmth and coolness without making changes to lights or textures.
Now we have our light and exposure settings set up we should make sure that our main light is actually acting as a Mental Ray physical light and the color is using the kelvin scale, making it easier and more accurate to set the warmth or coolness of the light.
Select the light and make sure you're in the attribute editor (CTRL+A). Under the Shadows dropdown, tick the box Use Mental Ray Shadow Overrides. Under the Shadow Map Overrides section, click Take Settings from Maya, and just adjust the values to the ones in the image.
The important values are Sample, which controls the quality of the shadow, and Softness, which lets us control whether the shadow is sharp or soft. With a bit of trial and error we can adjust it to produce a shadow that looks realistic for our setting.
Under the Custom Shaders dropdown, tick Suppress All Maya Shaders, and click the icon next to Light Shader.
The Create Render Node menu will pop up and there will be a bunch of tabs along the top. On the right hand side there is the Mental Ray tab. Under this scroll down to Mental Ray Light, and select Physical Light from the list (See Image LightShader1).
You will notice the Physical Light attributes show up on the right, and we can leave them as they are. The only thing we want to change is the color. We want to use the kelvin scale, so click the icon next to Color and select Mib_cie_d from the mental ray lights list (See Image LightShader2).