Yes, I have heard that the full-zoomed FOV is most realistic, but as DmdSeeker said, it would be hard to fly with that FOV only.
I have mapped the "Toggle FOV" command to a button on my X45 throttle. that way I can cycle thru wide>mid>zoom very quickly. I also have "toggle gunsight view" mapped to another button. Between the two of them (with TrackIR) I can scan around very efficiently.
I know that doesn't really answer your question of which is most realistic; basically it isn't very realistic to fly a plane looking thru a small rectangular frame right in front of your face. Being able to easily flip thru various view options helps the immersion IMHO.
PS-I find I can spot distant planes better with the wide FOV
A simple calculation will reveal that indeed the most realistic FOV for most screen viewing distances occurs at maximum zoom (30 degrees). It comes down to this... whatever the subtended angle your screen appears to your eyes should be the game's FOV setting, in order that the game view scale with reality.
Most folks have their monitors at a distance which results in the screen width appearing to be 25-30 degrees. Which is why in such cases the true scale FOV would be zoomed all the way in. Of course, this is rather like tunnel vision, and therefore one generally uses the widest offered FOV.
At the risk of sounding tiresome, I've overcome this by viewing my 19" flatscreen CRT from the VERY close distance of ~11 inches. In order to get a comfortable focus, I wear 3.5 diopter (~11 inch focal length) reading glasses. Now the screen subtends an appearent angle of 80-90 degrees! As you can imagine, at the widest FOV of 90 degrees the view is pretty much at true scale, which is great for situational awareness. Even so, I still will zoom all the way in for long shots, target I.D., etc.
Yes, it really depends, do you want to see things on a 1:1 scale, or would you rather see as many things as you would with your real eyes? A person has roughly a FOV of 180 degrees with perephrial vision, and this is needed for full situational awareness in real life and a larger FOV in IL2 helps with this too, ie. a Larger field of view in game is more like real life.
Identifying aircraft and other details can be hard with a wide field of view depending on your monitor, this is why there is the "gunsight" view, which is also more like real life.. In terms of scale.
So you have a trade both have advantages and disadvantages, neither is exactly more realistic. It is best to patch your "normal" view to a button or hat, and flip it to gunsight mode when you need to examine something in great detail, such as identifying an aircraft, lining up your guns, or looking for your airfield. I have a 24" widescreen monitor, and to be honest, the gunsight view I think is a little bit larger than real life.
All these things depend on how large your screen is and how close you sit to it.
Since I have a large monitor and sit relativley close to it, I tend to use the 2nd to widest FOV available for normal flight, and switch only to the gunsight when I need to zoom in on something for increased detail and accuracy.
Even so, I would REALLY love to have the widest field of view possible at the closest to life scale as possible (this would be as close to real life in both regards as possible). So if I could get close to a 180 degree FOV and all the instruments and gauges would be a few inches wide and what not, close to a 1:1 scale, with my perephrial vision picking up some of the detail.. The immersion factor would be amazing.
One could do this with a projection monitor aimed on a wall, or probably better.. a curved half cylinder, so the edges would soomewhat wrap around the users head, going into his side vision.. Or then there is this, which I am currently considering picking up..
Triplehead2go seems like a reasonably priced solution, and would also end the Track IR vs Padlock debate! (not that I think a debate really even exists in that argument).
When we talk about the size of planes and objects around us, closest to reality would be fully zoomed in.
When we talk about field of view i think fully zoomed out would be the best. I fly with the widest field of view most of the time unless i'm about to shoot a plane that's in my gunsight or i'm searching for ground targets or trying to identify a plane.
In wide field of view you get better sense of motion and can get better deflection shots.
I use the default FOV while cruising and doing most other mundane pilot actions. Otherwise, I'm all over the place with FOV. Whether zoomed in to spot ground targets or to ID an aircraft or zoomed all the way out to look over my shoulder. I use my FOV toggle more than just about anything else except for my throttle setting.