The FOV is no more than the distance of the view that has the game.
They, unfortunately, has 1 against (but most Pro)...

Pros:

• It's good for the eyes (since the default of video games, often hurts the eyes)
  
• Comfortable (very comfortable to look even better around)

Cons:

• Very often, for low frequency computer, it could happen to notice a bit of lag, but this happens in a matter of probability, so this is not a real counter).

The change can be seen immediately (Especially if you set a high number) of Team Fortress 2, there are maximum values​​, then we can set a custom value.

In this first step we would see as you turn the console on Team Fortress 2 :D

1) Go to the library into steam



2) Click with the right mouse button on "Team Fortress 2" and click on Properties, after that you have to click on "Change boot settings" and a window will open, in that window you enter the following code "-console"



3) Start the game
4) Go to "Options" and click on "Advanced"
5) Click on the check mark that says "Enable developer console".



6) Given the okay and down the options you will find a key to be issued, click on "Edit" and select the key that you want to open the console (I use "\")

1) Now we just have to restart the game and then enter the following commands in the console:
"viewmodel_fov [enter the value you want]"
"fov_desired [select a value from 70 to 90]"
(WITHOUT THE QUOTES!)





2) Press Enter.



3) Done!

70 Default

90 MAX VALUE

Here are some pictures where I show the difference between a few different FOV's:

1- Fov to the value of 70 (viewmodel_fov 70):



2- Fov to the value of 100 (viewmodel_fov 100):



3- Fov to the value of 1000 (viewmodel_fov 1000):



I, as always, reccommend the second showed option (100), since I think it's the best one! :D

Q: "Can I change the fov at any time of the game?"
A: "Of course! Just open the console".
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Q: "Do I risk getting banned?"
A: "No, if it happens to you, please contact the Steam Support, they will give you the right information".
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Q: "Is it possible to change the FOV using a controller?"
A: "Yes, the FOV will reactivate"
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Q: "I ​​would like to reset the FOV, how can I?"
A: "The default fov is 70, and there are no limits, so if you want to reset it,, start the console and enter the following commands:
"viewmodel_fov 70" and "fov_desired 70" , after that you will have the default FOV. "
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Q: "Is it possible to change the FOV on an MAC?""
A: "Yes, of course :)"