What is eye relief, exit pupil, field of veiw?

[5.56 JC]

I have been looking at a Trijicon TA31F on the website What do the following mean?

Eye Relief (in) 1.50
Exit Pupil (mm) 8.00
Field of View (°) 7.00
Field of View @ 100yrds (ft) 36.80



I cant find anything on the website and am not familiar with magnified optics at all.

Thanks

[markm]

It's how far your eye should be from the optic to get a full field of view.

[5.56 JC]

Does anyone know what the other ones mean?

[markm]

I'll take a stab at field of view.

If you looked thru the scope at a big wall (hypothetically), and that wall was 100 yards away from you, then you would be able to see a 36.8 foot circle section of the wall in your optic.

[Sidewinder6]

I have been looking at a Trijicon TA31F on the website What do the following mean?

Eye Relief (in) 1.50
Exit Pupil (mm) 8.00
Field of View (°) 7.00
Field of View @ 100yrds (ft) 36.80



I cant find anything on the website and am not familiar with magnified optics at all.

Thanks

I will try to help, perhaps we have some snipers who are up on optics who can add if my description is confusing:

Eye relief: Is the distance you can back away from the lens and see an image. You wound not want your eye to have to touch the lens in order to see or have your eye lashes make you crazy. So the distance on this scope is an Inch and a half.

Exit Pupil: A bit more abstract but try this. Look through your scope, then back away about one foot. The 'Image" your scope is projecting is actually floating between your eye and the glass surface itself. This 'disk' for lack of a better name is the Exit Pupil and on this scope, this is 8mm away from the surface of the glass. This is the sweet spot that you can see the focus of the optics.

Field of View: means that your scope has a 'beam width' of 7 degrees when you look out and...

At 100 yards, this is 36.8 feet. If you move back to 200 yards, this becomes 73.6 feet. You get the gist.

I hope this helps.

[jmart]

Exit pupil is a mathematical computation of the objective lens diameter (the big one out front) divided by the magnification. Since teh ACOG is a 4X scope, and the exit pupil is 8mm, the objective lens must be 32mm.

25mm = 2.5 cm = 1", so 32mm = 1. 23" or thereabouts.

The importance of exit pupil is it defines how precise your eye alignment needs to be behind the occular lens (the little one at the back). An 8mm exit pupil is pretty generous, essentialy it defines a shaft of light that the image is contained within, and the larger the diameter of this shaft of light, the more margin you have with lining up behind it. Your eyeball can wander across this 8mm shaft and still see the full image.

Just for comparison, lets assume you have the same 32mm objective, but let's crank magnification up to 16X. Pretty cool, eh? Well now you have a 2mm exit pupil. It forces your eye position to be right behind the lens in perfect alignment, get off a bit and you see the black shadow.

The other tidbit, physiologically speaking the max your pupil can dilate is around 4 - 5mm, depending upon age. The pupil sets the limit on how much light can enter your eye, but when a scope's exit pupil is smaller than this 4- 5mm max, it kind of demonstrates how critical it is to get your eyeball lined up properly. Exit pupil's greater than the 4-5mm provide greater margin for error, you don't have to be perfectly lined up behind it. Also, your pupil doesn't dilate to 4-5mm until darkness sets in; in bright daylight it's much smaller so that big exit pupil provides greater margin yet.

[decodeddiesel]

Sorry to bump an old thread, but that is a great explanation of exit pupil! Well done jmart.

[Submariner]

And when added to this thread gives just about everything one might want to know about a TA31F.