Eye relief..exit pupil..head movement "forgiveness"

[JCM]

What factor(s) established how "forgiving" a scope is?  I don't know the correct terminology, but by forgiving I mean a scope that I can look through and if I'm at an odd angle (to a certain extent) still see a good picture.  Basically a scope that if my head isn't in the exact same spot I'm not going to loose the entire picture.  Is it eye relief, the size of the exit pupil, power, a combination....?

I'm looking at new scopes and it crossed my mind that one outstanding factor I don't like about my current scope, is that if I move my head slightly I loose the picture completely.  Any feedback on scopes with good or poor "forgiveness" would be appreciated at well.

Thanks,
JCM

[jackfish]

I think it is called "eye box" and determines how easily one can pick up and maintain a full sight picture.  Leupolds seem to be able to afford an easily acquired sight picture.  Maybe I am doing something wrong but every Nikon and Bushnell Elite I have picked seem to be very "unforgiving" and some even look like looking down a tube as the sight picture does not fill up the eyepiece.

[Graybeard]

Never heard the term "eyebox" before. That's a new one on me.

I think to answer your question it is mostly a matter of exit pupil. The larger the exit pupil the more lattitude you have to move your eye side to side or up and down before you lose the image or "black out". Exit pupil is purely a factor of scope magnification and objective size. Divide the ACTUAL (not stated) magnification into the objective size in MM and the result you get is the diameter in mm of the exit pupil.

GB

[Dave in WV]

Actually "eye box" is the window of eye relief YOU can use and get a full view. It's a combination of eye relief and exit pupil. Both affect the sight picture. The exit pupil is the more controlling factor. Some scopes are more eye position critical than others. It seems some people are effected less by certain scopes than others. It may be a case of what you're used to. A person that gets used to a Leupold with a lot of eye relief is aggravated with a scope with less eye relief and a person that got used to the scope with less eye relief finds certain Leupold scopes bothersome. I find getting the scope mounted the correct height so when I shoulder my rifle I looking through the scope properly makes using my scopes easier. Sometimes you can't get the scope low enough so raising the stock comb heigt is the way to go. I did just that on my M52 .22 with a Bear Creek comb kit. It is not permanent and doesn't hurt the stock finish.

[Bushnell Boy]

I haven't heard of an "eyebox" before but GB is right about the exit pupil. The larger the exit pupil the more forgiving it is. Any exit pupil over 4mm or 5mm is usually easy to look through.


To find the size of your exit pupil divide the size of your objective lens by the magnification. (ex. 10x50 = 5mm exit pupil) This is an important formula to remember when purchasing optics. If you need to see well in low light then you will want something with a large exit pupil. The average persons pupil fully dilated is 4-5mm in diameter. So in order for your eyes to take in all the light they can you would want something with at least that size exit pupil. If you are only using your optics in lit conditions then your pupil will be constricted and the size of the exit pupil won't matter as much.