Since there's been some discussion regarding changes in the character zoom mechanic I decided to jump in and explain what are we trying to achieve. 

We should probably start by asking the question "Why have a characters-eye zoom in the first place?". It's the old problem with emulating a 3D world on insufficient hardware. The human field of vision (fov) is around 190° and the area where the vision cones of both eyes overlap is around 100°.  Unfortunately, most of todays monitors viewed from a regular distance usually tend to cover only 45°of human fov in real life. This means that if you want for target on screen to appear in real-life size you are only able to display around ~1/2 of what you would see in reality, stereoscopically. 

And so as a designer you have to choose - Should I display objects in the distance properly but sacrifice the overall vision or set the fov to 100° but deform the whole picture? The trick of Arma is actually not to choose and instead introduce an "eye zoom" instead. This way you can keep the surrounding awareness by setting the default fov to 100°, but when necessary to perceive a depth of field properly occurs (ie. you are shooting), you can "zoom in" to 45°.


0.57 Unzoomed Eye Vision


0.57 Eye Zoom
 

But is it ok to force fix a fov on players? We thought not. Not only because 100° fov does not feel right to everyone, but some players can't even physically play with it. (Motion sickness, performance of PC, different monitor setup...). So the FOV slider was introduced and with it multiple problems we are ironing out now.
The most important step was to even out players by moving fixed fov to ironsights. This way you can most of the time play with whatever fov you like, but when the fov becomes a matter of life or death (shoot outs) it is set same for everyone to keep the game fair. 

We know that zoomed fov or ironsights must be 45° because it emulates the eye and we stated earlier that 45° is realistic. But what should the unzoomed fov be? It can't be higher than a number the player can set through FOV slider. (This way would going into iron sights actually shows the unzoomed picture which is definitely not something you would desire). So the fov of ironsights should be also the the smallest fov we allow players to set by the fov slider. 

We decided to set range of fov slider from 60° to 90°.


0.58 Eye Zoom

It's important to keep in mind, that double pressing + or - extends it to 45° or 105°, so the range is not so small as it might appears. It also doesn't matter what is your current fov - double pressing + key will always set it to 45°. This means you can quickly switch between observing surroundings and focusing on objects "modes", while being able to play with your prefered fov for most of the time. I belive this descision helps equalize players and reduce fov slider abuse.