While OFP doesn't have an in-game setting that allows you to adjust your field of view (FOV) aspect, this can be manually done by editing file Userinfo.cfg with a text editor. The file can be found in OFP's \Users\your_player_name subdirectory.
In the file, you'll find two FOV related statements: fovTop and fovLeft. The fovTop statement sets the vertical FOV aspect ratio from top to bottom, while fovLeft sets the horizontal aspect ration from left to right.
By default, they're set to control the FOV aspect ratio based on the screen resolution you play OFP with. For example, I play OFP at a resolution of 1600x1200 pixels. 1200 is seventy five percent of 1600. So OFP sets my FOV statements to fovTop=0.750000 and fovLeft=1.000000, for a 0.75 to 1 aspect ratio.
Let's say you want to increase your FOV by, let's say, fifty percent. Simple! Just multiply the FOV statement values by 1.5. In the above example, that would mean setting fovTop to 1.125000 and fovLeft to 1.500000.
Compare the results for yourself. The first pic, below, is a view from the southern side of Chapoi on Malden, looking due north, taken with OFP's default FOV aspect ratio:
Now, here's a pic, taken from the exact same location, but with OFP FOV values increased by fifty percent:
Impressive difference, no? Sort of like having fish eyes. Of course, you could go wild and increase your FOV by five hundred percent. However, I have the feeling that anything above a twenty five or fifty percent increase will make your gameplay visually less enjoyable.
Is this cheating? Well, it could be, if over-abused. But, as I said, there's no fun in playing with ridiculously high increases in FOV. So, if you feel it will improve your game, try a FOV increase of twenty five or fifty percent and see if you like it.
Whatever you do, if you adjust OFP's FOV, make sure you always maintain the original corresponding ratio between the fovTop and fovLeft values or you'll have one ugly warped and skewed FOV to play with.
With thanks to OFP guru Kegetys for pointing this out to the player community.