I will show you how to add depth of field to a scene in 3Ds max.
First of all you need to create a very simple scene (or load a scene to test this out).
This is an example of a scene I used to test the depth of field
Once you have your scene, using the perspective viewport, navigate around the scene until you have a good angle to test this (Objects near and far from this location works best).
Press and hold middle mouse button not move the view in the x and y axis and holding alt and middle mouse button will rotate around the scene.
Once you have found a good spot press CTRL + C
This will create a camera, in the top viewport you should make sure that the target of the camera is somewhere in the middle of all your objects.
To change the camera target, you should click the camera and in the modify tab, under the parameters there should is “Target Distance”. Note: you may need to scroll down in the parameters list to see this option.
Now, for default scan line rendering you will need to go to..
Rendering > Effects, Then in the effects window click Add > Depth of field.
Choose the cam using the “Pick cam.” button. Also choose the camera target using the “Pick node” button.
In the focal parameters select “Use Camera” You settings window should look something like this…
When you render now you should automatically have depth of field enabled. (F9 to test render)
This will NOT work with some over effects in 3Ds max. For example you cannot use this effect while having fog in a scene.
Now for the mental ray renderer, set the scene up similar to the one above, but instead of using a camera, just keep your perspective viewport window.
By pressing F10 or clicking Rendering > Render setup, go to the render tab and scroll down until you see depth of field (perspective views only)
The f-Stop is the same as a camera, I will breifly explain what this is does, If it is at f12 there will be more objects in focus, the focus plane will be greater. So if you wan’t to focus just on the tip of a pencil, the lower the f-stop the better. Another example is if it was a group photo, something above f12 would be good as you wan’t everyone in focus and because they might be standing in different positions its best to increase the f number.
The rest of the settings here are self-explanatory, the focus plane is like the camera target while using depth of field with default scanline render type.