Mental Ray Rendering Final Gather basic

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Render created with Maya Render

Render created with Mental Ray Final Gather

Install plugin, if you do not see Mental Ray options
Keep in mind that Autodesk did not develop Mental Ray; it is a plug-in for Maya, so you may have to enable it in the Plug-in Manager before you can see it as an option in your Render Settings window.
     To enable the plug-in:  Window>Settings/Preferences>Plug-in Manager
    
Check both the Loaded box and the Auto Load box next to Mayatomr.mll and xgenMR.py

Final Gather
Final gather is method of simulating global illumination.

In the Perspective view use View->Camera Attribute Editor...
Under Environment
Change the black Background Color to a lighter color. The background will be used to generate ambient light when you select final gather

Create 5 sided cube (Create NURBS Primitives->Cube, delete 1 side)
Create a sphere
Apply material - Blinn or play with the Mental Ray shaders

Open Windows->Rendering Editors->Render Settings or press render_settings_button

Under the Common
Tab:  down at the bottom: Render Options
     Uncheck Enable default lights You will render with light reflected from background.

Choose Render using
mental ray  (top of Render Settings)

Select the Quality tab
Select Sampling-> Indirect Diffuse (GI) Mode-> Finalgather

Render an image

Lights
Try adding a Mental Ray light:
There are additional 4 lights that work with Mental Ray (not Maya Software render):
     1) Select an object to be used as a light, ie NURBS sphere, Create->Lights->Object Light
     2) Create->Lights->Physical Area Light This light shows up as an object.
     3)
Create->Lights->Physical Sun  Rotate to orient, 0 degrees = no light, -90 degrees noon
     4)
Create->Lights->Environmental Sky Change settings under View->Camera Attribute Editor...
         for the Persp window. mia_physicalsky1 tab, You can turn this off if you do not want it.
     5)
Create->Lights->Environmental Image (IBL) Search google for image based lighting images,
         Look under lights in the Hypershade to edit. This will shade your object.
         You can hide the object, look under render Stats, uncheck Primary Visibility.

Maya Lights:

Create a light with shadows, under the light's attributes select:
 Shadows -> Raytrace Shadow Attributes
              check Use Ray Trace Shadow
 Light Angle 
.4  (soft shadows)
 Shadow Rays  40 or more (gets rid of grain, higher than slider)
 Ray Depth Limit  1, higher if you need to see shadows in reflections.


Get Rid of the Speckels
Open Windows->Rendering Editors->Render Settings or press render_settings_button
Scene tab
Under Cameras->Environment
Uncheck Emit Environment Light


Presets:

Open Windows->Rendering Editors->Render Settings or press render_settings_button
Top menu
Presets->Load Presets
Default
     Overall Quality .25
     Lighting Quality 1
     Indirect Diffuse (GI) Mode off
     (MILA) Material Quality 1
     Filter Gauss
     Filter Size 3, 3
     Reflection 4
     Transmission 4
     Max Trace Depth 6

FinalFrameEXR
     Overall Quality 1.5
     Lighting Quality 1
     Indirect Diffuse (GI) Mode off
     (MILA) Material Quality 1
     Filter Gauss
     Filter Size 2, 2
     Reflection 4
     Transmission 6
     Max Trace Depth 10

** Preview Save rendering time
     Overall Quality .01
     Lighting Quality 1
     Indirect Diffuse (GI) Mode off
     (MILA) Material Quality 1
     Filter Box
     Filter Size 1, 1
     Reflection 4
     Transmission 4
     Max Trace Depth 6

Production
     Overall Quality .6
     Lighting Quality 1
     Indirect Diffuse (GI) Mode off
     (MILA) Material Quality 1
     Filter Gauss
     Filter Size 2, 2
     Reflection 4
     Transmission 6
     Max Trace Depth 10



Here are a few great guides for Mental Ray specific shader settings:
http://www.nvidia-arc.com/fileadmin/user_upload/PDF/arch_and_design.pdf
http://docs.autodesk.com/MENTALRAY/2015/ENU/mental-ray-help/files/shaders/architectural/arch_mtl.html