I play Rage at default of 80 and it feels like walking around with a box on my head. Upping it to 100 makes it feel right and natural. On the other hand playing Deus Ex: Human Revolution at 100 FOV feels like playing with a fishbowl on my head, while 80 feels normal and natural.

Shouldn't 80 be 80 and 100 be 100?

What's your ideal FOV and why are they different from game to game?

FOV can be implemented vertically and / or horizontally, so that's why you see difference in different games.

86 horizontal is ideal for 16:10 displays ay 1440x900 resolution.

Given that the number should refer to a number of degrees, yeah it should be the same.

My first guess is it could be something to do with the way the game treat aspect ratios. It would depend on whether they treat 16:9 as 4:3 with extra view at the sides or as 4:3 with the top and bottom cut off.

EDIT: Sounds like Elenarie is saying something similar to me so I guess I might just have been ninja'd.

FOV? Field of Vision? Frames of ...? Ferrets Obscuring Voles?

Yeah, field of vision or view. I prefer ferrets obscuring voles though.

I find that modern Bethesda games work best for me at FOV 100, which coincidentally also decreases the chance of getting a headache from playing first-person games.

80 sounds low. I think UT2004 defaulted to 90 and I would up it to I think 100. I would have to check if it allowed 110 which I might have used if it allowed it. I definitely thought being able to see a little more in the horizontal axis is a big help. But then that was in 4:3 aspect days. I would think that wider monitors would need a wider field of view not a lower one.

I'm now real curious how FOV is determined. The output aspect is something that gets calculated so there is room for an error, but its highly unlikely. It sure seems like it should be consistent across games.

Any chance some of it is perceptual? Like one game is more demanding on the horizontal axis and it feels like you are missing out not being able to see wider? Or could one game be stuck using a 4:3 resolution and the other say a 16:9 one?

It's not that easy though, I know Call of Duty's "55" is not really 55 because they figure it out vertically or whatever. Rage and Deus Ex 3 both do it horizontal though, hence the higher starting numbers.

It seems like different games just feel different, some kind of geometry thing. Rage's default is around what you suggest (and what feels right for Deus Ex) but it feels really closed in and confined in comparison.

Skyrim is another example. The default is too boxed-in, but upping it much at all makes it look really fisheyed.

Well, yea, there will be difference even if they calculate FOV using the same technique. Different games have different camera angles and locations, so that needs to be taken into account too.

I can never tell how various games measure that. I'm on a 5:4 monitor, while Minecraft feels good on 80-85 on fullscreen, though it's irritating when in a maximized window and DXHR stops being irritating [turning around to suddenly have a wall right in my nose that's 0.5 meters away] at 100. So, basically, it's trail and error for me.;)

The "natural" FOV is the angle between the two edges of the screen. This depends on the size of your screen and how far from the screen you sit, but there's plenty of margin for error so the fact that people sit differently isn't much of a problem. (note that this explanation applies mainly to first-person games - for third-person, the position of the camera in the world relative to the screen is more important. I can try to explain the exact mechanics if anyone's interested).

You can also set the FOV to something other than the ideal for certain special effects. For example, a narrow FOV conveys a sense of focus - you often see this transition when using iron sights. A wider-than-normal FOV can convey a sense of speed.

Hah, indeed, playing Team Fortress 2 as a Scout, using 90+ FOV is fun!

It depends on the game, if you play something like Arma 2 you want at least 120° horizontal FOV with 16:9 ratio.
If you play a game like Deus Ex HR, 90° is probably enough.

Indeed, I remember binding a FOV change to a key in Quake 2 multiplayer to help with sniping people across the map with a railgun. Ahh, the days before people learned to run their maps with the -nofov tag...

How did you get that number? Also, how do check if a game is based on horizontal or vertical FOV? :)