Question about exit pupil for scopes with really high magnification.

[Bravo 4]

I didn't want to hijack the thread about the 8-80x56mm March scope so I started this one.
If it's supposed to be a simple formula of dividing the power magnification into the objective lens size to get the exit pupil number, do these scopes have a negative number? If an exit pupil number of 7 is about as good as it gets for the average human eye then how would these scopes fare?
Is it simply like putting a reticle/erector tube and some turrets on a spotting scope? I've seen spotting scopes that appeared to be higher powered riflescopes (reticle and all) just without turrets.

One more question I would like your opinion on; why don't they make a LR/ELR laser range finder built into a spotting scope? I mean the main benefit of having magnification in a riflescope is so the shooter can have a finer aiming point on a target, and besides beam divergence one of the biggest gripes from the long range crowd is precise aiming (especially smaller targets at extended ranges).
Maybe I'll send Aaron Davis an email and get his take on it from an engineer's perspective. As a matter of fact, I know another engineer on this site and will send him an email. I can see these being rather expensive, considering the cost of a good spotter combined with the cost of a good range finder.

 

[FEENIX]

lightbulbHopefully, Bruce Ventura chimes in!lightbulb

 

[LONGSHOOTER]

0.7 is not a negative number, just less than 1.0.

 

[Bravo 4]

0.7 is not a negative number, just less than 1.0.

Correct, good job using a calculator. My point is- is there a point where it no longer matters? If you go above 7 it supposedly has no benefit, what about the opposite direction? Now from what I've been told/read there are optical benefits from having a larger objective other than just the exit pupil, so how does it effect the optical performance if the objective size and magnification sizes are reversed?

Or am I just thinking too much?
Or as longshooter would put it, not enough...just kidding

 

[LONGSHOOTER]

I don't know what you are looking for, other than exit pupil sizing. Exit pupil size that is below the size of YOUR pupil is probably not desired. That, and you might need to be more precisely located behind the exit pupil.

Perhaps on a bright day, target shooters might be able to accomodate a small exit pupil.

You might ask March some questions.

 

[LONGSHOOTER]

24hourcampfire.com - "THE OPTICAL TRIAD: MAGNIFICATION, EYE RELIEF, AND FIELD OF VIEW" by John Barsness

For your reading enjoyment.

 

[bruce_ventura]

Four things to keep in mind:

1. The resolution of the adult human eye is about 1 MOA (20/20 vision). Objects smaller than this size are just blur. Younger people can have a little better resolution, say about 0.7 MOA.

2. The resolution of a really good telescope is loosely called the "diffraction limit". For a 56 mm objective telescope the resolution is about 27 times better than the adult eye, or about 39 times better than a young, exceptional eye.

So, above a magnification of roughly 33X, give or take, a 56 mm objective telescope is magnifying blur, but it's not providing any more detail about the target to someone with good vision. Below that magnification, the eye is the limiting factor.

If you have vision problems that cannot be improved with correction, then additional magnification can be helpful. For example, an adult with 20/40 vision with correction would benefit from a 54X telescope.

3. Brightness in daytime decreases dramatically above 33X for most people. At a magnification of 54X, the image through a 56 mm objective telescope is roughly 1/4th the brightness perceived by the naked aye. At 80X, the brightness is about 1/9th that of the naked eye.

4. Glare due to "stray light" increases dramatically with magnification in rifle scopes. For example, glare is more noticeable at 20X than at 10X. Even for a good (low glare) rifle scope, stray light rays are concentrated just outside the exit pupil. When the exit pupil is smaller than the eye pupil or the eye is not properly aligned with the exit pupil, this stray light gets into the eye pupil and washes out the image.

So, unless you have vision problems, magnification above about 33X for a 56 mm objective rifle scope is not beneficial, and usually degrades the image rather than enhancing it.

However, we live in a society where bigger is better regardless of physics, and marketing people exploit that fact.

 

[Bravo 4]

Now that's the type of info I was looking for, thanks Bruce. The last bullet comment just confirmed my suspicions.

Longshooter,
Thanks for attempting to answer my request for further information. I have trained combat shooters for many years and believe I pretty much have the basics down, as do many shooters before I get up in front of them. I obviously don't know everything, but knowing the little details (like in Bruce's comments) are a part of what sets a good instructor apart from the rest. Well at least it makes me look like I know what I'm doing.

Thanks again guys for the info.

 

[FEENIX]

Now that's the type of info I was looking for, thanks Bruce.

I told you ... he always does.

 

[Bravo 4]

Yep, you were spot on.

 

[LONGSHOOTER]

......

Longshooter,
Thanks for attempting to answer my request for further information.

Attempting?

Listen, you get the light cone smaller than your own pupil, you start to experience problems. That is why I said perhaps you should contact March for a definitive answer to your very specific question.

I don't appreciate a condescending attitude.

But, this is the net, so ya git what ya git.

 

[Bravo 4]

Actually my comment was sincere and not meant to be condescending, but like you said it's the internet.

 

[FEENIX]

Actually my comment was sincere and not meant to be condescending, but like you said it's the internet.

Sadly, even the best of intentions get misconstrued.

 

[LONGSHOOTER]

Sadly, even the best of intentions get misconstrued.

Not.