Home Forums Hunting & Shooting Hunting Optics light gathering?

does this make sense? any idea where this or something similar be found?

. I read an article that said 6x42 was the apex of light gathering, power and objective size. I can't explain it but to get the same light gathering with more power, it would take an 8x56 I believe. It has to do with the ratio and something to do with one's pupil. capt david

Exit pupil is objective diameter divided by power, so both the same in this case 7mm. None of them "gather" light, just pass it thru. The bigger the exit pupil the more the pass thru of light, all else equal, coatings and such.

Light gathering is a misnomer. Light transmission, expressed usually as a percentage is more accurate.

A few years ago I discovered I enjoy comparing optics. Following is some info about exit pupil.

January 7, 2012 exit pupil is a mathematic measurement. The idea a larger exit pupil results in better low light vision is a MYTH!
For my fun and entertainment I laid out some binoculars and a scope on some sand bags for a low light comparison. After focusing the bins on the deer antlers 131 yards away I decided to see what was the lowest setting I could make out the forks with the scope. My criteria was would I shoot at the deer which carried them? The exit pupils have been included to show how irrelevant they generally are.

Tasco World Class 4-16X40 @ 7X = 5.71 exit pupil


After this I turned it up to 8X to match the Bushnell Ultra HD 8X42 and waited.

Binoculars Exit pupil

Minox 15X58 - 3.87 mm
REI 10X32 - 3.2 mm
Bushnell. 8X42 - 5.25 mm

At 5:10 the 8X42 binocs and the scopes set on 8X were out.
Tasco on 8X = 5.00 exit pupil

I turned up the scopes till I could make out the forks again.

Tasco - 14X Exit pupil: 2.86

At 5:14 I had to turn up the scopes again.

Tasco - 16X - Exit pupil: 2.5

At 5:15 the REI 10X32 were out. Exit pupil 3.2

At 5:16 the Tasco was out. Exit pupil 2.5 lasted longer than the 3.2.

The Minox 15X lasted until 5:20. Exit pupil: 3.87

At this almost too late moment I wondered how the Swarovski z5 5-25X52 would fair so I ran to get it. I could not see the antlers until they were on 25X and they lasted only about a minute. The exit pupil calculates to 2.08mm and lasted longer than the 3.87.

The ratio is called exit pupil.

I wrote this piece a long time ago. It is long, but skim through it. There are several sections there on optics. I am slowly working on an update, but most of it is still relevant.
http://opticsthoughts.com/?page_id=122

As a general rule, whenever you see something posted by Ringman, assume that he is not the same species as the rest of us and whatever he says is not applicable to humans.

ILya

If this is the same guy who was at Optics planet he is not always reliable. He changed some of my posts. I could not understand some of the posters responses until I went back and read the changed posts. He told people I worked for Tasco when the closest I came to Tasco was buying Tasco scopes. It's really sad he is the way he is toward a potential .com friend.

koshkin,
If you are not that guy, I apologize for the above. If you are that guy I challenge you to post your refuting comparison, please.

Okay, some things to consider with light transmission that the grand pooba and others don't seem to understand-

Light transmission has to do with lens coatings and number of lenses in a group and a scope- all other things being equal.

Each lens is going to absorb a certain amount of light, depending on the quality of the lens coatings on each lens. If you have better lens coatings on one scope with the same amount of glass in it than the next scope, it should pass more light- all other things being equal. Since fixed power scopes have substantially fewer lenses in them, they should pass more light if the coatings are the same and all other things being equal...

Cheaper scopes usually won't pass more light because they use coatings that are "less expensive" than the latest coatings on the higher end scopes. These days the high end coatings and their application procedures are the single highest expense in building a scope from what I've been able to learn. So, if you want a cheaper scope to pass more light, you would need to either invest in the latest coatings and learn how to apply them- therefore raising your price point, or use less glass in your lens groups... you don't get something for nothing....

^^^ All This. I want to add that Glass Quality trumps them all. FL,HT and other quality glass is a commodity and is not cheap.

Some short comments:

1) While there used to be an enormous difference in glass/coating quality in scopes of various prices, like all optics that difference has shrunk considerably. I have tested scopes costing less than $500 (often much less) in the past few years that are only slightly less "bright" than the brightest scopes available.

2) The price of the very brightest scopes has gone down, as the glass/coating technology has spread across the world. A few years ago the very brightest scopes all cost over $1000. Now some cost less than $1000, often considerably less.

3) The reticle is more important in aiming in dim light than scope brightness.

4) Ringman may not just be a different species, but from a different world.

Worth repeating....

And that fact is getting lost on a lot of manufacturers including Germans and Austrians who should know better.

Perhaps not lost, but satisfying the buyer who insists that hitting the exact hair rules over planting a bullet into the heart right now and let’s see what happens.

The LR philosophy is the current darling of the rifle shooting sports and the Krauts are not about to ignore it.

Thanks, it is good to know someone else knows there is no such thing as gathering light. The coatings and number of glass lenses in the unit determines the % loss at the rear of the optic. Simply physics. Rusty

It's important to note your eyes will have a smaller pupil diameter as you age. Some folks might not be able to tell the difference between brightness on 6x42 vs 14x42 for no other reason than their own eyes aren't capable of capable of dilating more than 3mm. You might get advice that exit pupil doesn't matter from such folks.

If you're younger or feel like you have good eyes, you'll see the difference. Should be easy to test on your own.

I took my scope out and gathered a 5 gallon bucket of light

I prefer my scopes to be filled with little hunter/gatherers.....

Some don’t realize serious shooters are extremely visual critical. A .25 diopter change becomes immediately noticeable. To the average person on the street it is no big deal. There is more than exit pupil that comes into play with those who are vision critical.

What do you mean by "vision critical"? curious here

Agree that diopter adjustments play a huge role in getting a crisply focused reticle, but a sharp reticle will not affect brightness of your image.

Vision critical, where a .25 change is almost immediately noticeable in your everyday walk around vision and not only a focused reticle. Retinal light sensitivity differences between individuals irrespective of exit pupil. Some have spatial recognition ability over the average.

Vision critical.

All those with normal or even better are not equals with regard visual acquity or what that can “see”.

Sounds made up - like your explanation though. Think you mean to say some people might need to get their eyes checked to get the most out of their optics or out of their eyesight in general.

You're opening a whole other can of worms with spacial recognition ability. No doubt it exists, but that's something your brain learns - not something you get from a diopter adjustment.