IMPORTANT: Motion blur is better with original enbeffect.fx! Install this AFTER you've installed the main files!
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Depth Of Field: http://en.wikipedia.org/wiki/Depth_of_field


Screenshot DOF: Gives a very smooth DOF but also a big performance drop, only recommended for screenshots.

Gameplay DOF: Gives a decent smooth DOF and isn't very expensive performance-wise, recommended for normal gameplay and videos.


Auto-Focus DOF: Focuses on the object/area you look at and blurs everthing else,  recommended for screenshots/videos.

Static DOF: Makes a constant blur in the distance, recommended for normal gameplay.


To get a more heavy DOF, open the enbeffect.fx from your GTA IV/EFLC main folder and increase the PixelSizeMultiplier to 3. 
To get a more light DOF decrease the PixelSizeMultiplier to 1.
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Installation:
Extract one of the files inside one of the folders to your GTA IV/EFLC main folder.