Common user errors
Out of the reports we are receiving from our users, we have selected some of user errors which seem to be more frequent than others. Below is a list of the most common ones:
Using bitmap paging
3ds Max bitmap paging may excessively slow down rendering. Disable this setting by going to Render Setup > Common > Common Parameters > Bitmap Performance and Memory Options > Setup... and unchecking "Enable Proxy System" and "Page Large Images...". Then close 3ds Max, and start it again. From now on 3ds Max will remember this setting, but it is a good habit to always make sure this option is disabled.
Using wrong gamma settings
Wrong gamma settings may lead to unrealistic rendering and incorrect handling of textures or saved/loaded files.
Wrong Albedo (material brightness)
Wrong material Albedo, especially on large flat surfaces, may be the cause of very slow rendering or unrealistic look of the rendered scene.
See: What is Albedo?
Using big sphere or cylinder mesh surrounding the scene as environment lighting
Such scene setup, apart from being unpractical, will greatly increase rendering time.
The correct way to create environment lighting is by using environment settings - see: How to set up HDRI environment?
If you want to make a directly visible background different than the environment lighting - see: How to create background material?
Misuse of Corona Light material and Corona Material with self illumination
Wrong use of these two kinds of light-emitting materials may lead to excessive noise and slow rendering.
Placing lights behind windows
Artificially adding brightness to the interiors should be avoided as it may introduce noise, long render times and unrealistic results. It is recommended to use environmental lighting and optionally portals, which may greatly reduce render times.
Using wrong glass type
Generally, thick glass should be used for solid objects (liquids, vases) and thin glass should be used for flat surfaces (glass panels) and objects with very thin surfaces (soap bubbles).
Using refraction for leaves or grass materials
Never use refraction for leaves (and all other kinds of vegetation and geometry with no thickness). Use translucency instead.
Using Multi-Pass Effects in camera settings
Using these legacy settings may lead to restarting of the rendering.
Unless intended as an "artistic" effect, Ambient Occlusion should not be used for shading. For realistic purposes, it should be used to simulate "dirt" or to add different colors in concave/convex areas of the object.
See:How to add dirt effect to objects? , How to add AO pass for post-processing?
Using texture maps in Fresnel IOR instead of Reflection Color slot
To vary the reflectivity of a material, you should usually place a texture map in its Reflection > Color slot. When placed in IOR slot, texture values lower than 1 will be interpreted as 1/value. This allows using low dynamic range images as IOR textures without output manipulation. This has been introduced to improve compatibility with applications such as Substance Painter.
Placing falloff map in material's Reflection Color slot instead of using Fresnel IOR
While using the falloff map may be a correct way of creating customized reflectivity curves, for simple materials it is recommended to use the Reflection > Fresnel IOR value as Corona internally uses more advanced Fresnel model which is required for its shading models.
Using features of other renderers with Corona
Using features (plugins, options) available for other renderers is risky, and is never guaranteed to work.
Example: using V-Ray HDRI loader as environment map may lead to flickering when rendering animations with UHD Cache.
Wrong render settings
Default render settings should work well in most situations. Sampling settings should be changed only when necessary and when the user understands what he is doing.
GI vs. AA balance
Light Samples Multiplier
Max Sample Intensity
Max Ray Depth