Rifle Scopes Higher zoom rate - less brightness?

[Jayjay1]

Hey guys,
I´ve read and saved somewhere in my grey mass, that a higher zoom rate needs more lenses, and therefore it looses brightness.

So a scope with a 4 times zoom is generally brighter than a 6 times zoom and so on.
How does it come then, that a Swaro Z8i (92% LT) should be brighter than a Swaro Z6 (90% LT)?

Or do I get something wrong?

 

[762libertarian]

Hey guys,
I´ve read and saved somewhere in my grey mass, that a higher zoom rate needs more lenses, and therefore it looses brightness.

So a scope with a 4 times zoom is generally brighter than a 6 times zoom and so on.
How does it come then, that a Swaro Z8i (92% LT) should be brighter than a Swaro Z6 (90% LT)?

Or do I get something wrong?

Could be that the z6 is older, I don't know. I'd also guess that the LT numbers are marketed much like some bullet manufacturers handle BC.

Zoom ratios also make your scope heavier. I think they're overrated for some applications, especially LPVO's, that are supposed to go on lighter, more nimble rifles.

 

[Jayjay1]

So I assume that you mean it is correct, that a higher zoom rate generally comes along with less brightness?

 

[Makinchips208]

Hey guys,
I´ve read and saved somewhere in my grey mass, that a higher zoom rate needs more lenses, and therefore it looses brightness.

Not true. But it gets very complex really quick.
@koshkin is the one who can best explain. He has YouTube also, if you search “dark lord of optics”.

 

[Jayjay1]

Well, maybe specific is easier then?

How will the Swarovski Z8i 2.3-18x56 perform in low-light?

Its competitor for me is the S&B 3-18x42, but that scope is probably to new to get such infos about it, or compare it in brightness against the Swaro.

 

[carbonbased]

Are you specifically talking about scopes with the same top-end magnification? But one is 2x and one is 4x (for example).

It sure seems the higher one goes in mag, the darker the view. In general. Not sure if the magnification multiple also contributes.

 

[db2000]

Well, maybe specific is easier then?

How will the Swarovski Z8i 2.3-18x56 perform in low-light?

Its competitor for me is the S&B 3-18x42, but that scope is probably too new to get such infos about it, or compare it in brightness against the Swaro.

I agree with asking Ilya but I’ll point out your comparing 2 scopes with different objective diameters. 42 vs 56. That diameter certainly makes a difference in how much light is gathered.

 

[koshkin]

So I assume that you mean it is correct, that a higher zoom rate generally comes along with less brightness?

It can, but it does not have to. Generally, brightness is not a very useful term when it comes to riflescopes. Maybe this will provide some background:

An Official Journal Of The NRA | How Much Zoom Is Too Much Zoom?

An optic’s zoom range, more properly known as its erector ratio, is often a selling point, but what does it really mean?

www.shootingillustrated.com

ILya

 

[Jayjay1]

It can, but it does not have to. Generally, brightness is not a very useful term when it comes to riflescopes. Maybe this will provide some background:

An Official Journal Of The NRA | How Much Zoom Is Too Much Zoom?

An optic’s zoom range, more properly known as its erector ratio, is often a selling point, but what does it really mean?

www.shootingillustrated.com

ILya

Hi ILya,
it did and it did not somehow, in terms of a direct answer actually.

But thank you very much anyways, I´ve read a lot of your posts inhere and have seen quite a lot videos on yt which helped me to decide in the past.

As both scopes are hunting scopes, there is no chance that you might review them in the very-very-very near future?

Am just joking.

The Swaro has a 8 times zoom with a 56mm objective, the S&B a 6 times zoom with a 42mm objective, both have an 18x as their highest magnification.
On paper the Swaro has an EP at 18x of 3,111mm, the S&B comes with 2,333mm, which may make a big difference, especially how finicky it is to get behind it.

But according to the brightness and in regards of your article it might be, that a lower zoom ratio (some manufacturers say not more than a 5 time zoom) helps with brightness.
Might be, not given.

Back to my both scopes, it´s a PITA and I´m undecided.
It would help if I could compare them side by side, which is very unlikely over here, on the countryside in Germany.

Have a great one,
Jay

 

[koshkin]

Hi ILya,
it did and it did not somehow, in terms of a direct answer actually.

But thank you very much anyways, I´ve read a lot of your posts inhere and have seen quite a lot videos on yt which helped me to decide in the past.

As both scopes are hunting scopes, there is no chance that you might review them in the very-very-very near future?

Am just joking.

The Swaro has a 8 times zoom with a 56mm objective, the S&B a 6 times zoom with a 42mm objective, both have an 18x as their highest magnification.
On paper the Swaro has an EP at 18x of 3,111mm, the S&B comes with 2,333mm, which may make a big difference, especially how finicky it is to get behind it.

But according to the brightness and in regards of your article it might be, that a lower zoom ratio (some manufacturers say not more than a 5 time zoom) helps with brightness.
Might be, not given.

Back to my both scopes, it´s a PITA and I´m undecided.
It would help if I could compare them side by side, which is very unlikely over here, on the countryside in Germany.

Have a great one,
Jay

I do not review Swarovski/Kahles products, so probably not.
I do have a 3-18x42 S&B on hand and the review is coming out soon.
If your primary concern is low light performance, you want to go with a larger objective. S&B Polar is a good option. 56mm Leica Magnus is really excellent as well.

ILya

 

[Jayjay1]

I do not review Swarovski/Kahles products, so probably not.
I do have a 3-18x42 S&B on hand and the review is coming out soon.
If your primary concern is low light performance, you want to go with a larger objective. S&B Polar is a good option. 56mm Leica Magnus is really excellent as well.

ILya

Thank you for your answer.

I hope I get to know when your review of the 3-18x42 S&B comes out!

Just for my curiosity, what´s the reason that you don´t do anything about Swaro/Kahles?

 

[NateVA]

Just for my curiosity, what´s the reason that you don´t do anything about Swaro/Kahles?

I don't want to opine on his Kahles reasons (not sure if they're Swaro-owned or what) but I believe he's said that he will not review any Swarovski products anymore due to their bullshit patent on FOV over a certain number of degrees in rifle scopes. They don't enforce it on US companies but I believe that's why, for instance, you get a different FOV for a S&B 6-36x56 depending on whether you're in the US or Europe. It's a wonder to me that Schmidt and Bender haven't taken Swarovski to court over it (have they?).

 

[RUN8]

Rifle scopes are like any other magnified optical system.

The larger your objective diameter the more light transmission you will generally get. Lens coatings and lens or mirror quality do play a role, but all else being equal a bigger objective lens or mirror is going to be brighter and support higher magnification without serious image quality issues like being dim.

A 42mm Objective gives you 1385.4 square mm of lens, and a 56mm gives you 2463 square mm. So the 56mm has a 78% larger lens area to transmit light.

That’s a big difference in raw lens size that minor differences in lens coating performance are not going to overcome.

 

[Jayjay1]

I do not review Swarovski/Kahles products, so probably not.
I do have a 3-18x42 S&B on hand and the review is coming out soon.
If your primary concern is low light performance, you want to go with a larger objective. S&B Polar is a good option. 56mm Leica Magnus is really excellent as well.

ILya

Well, there you have it.

1. I didn´t know about the Swaro FOV - thingy, I totally agree, that´s ridiculous.

2. Welly-well, my scope right now is the S&B 3-12x54 Polar, now you got me on that.
According to RUN8 it will be a huge downgrade in brightness, if I go with the S&B 3-18 Meta (zoom rate and objective diameter).

So I probably stick with it, or do make a comparison to the 4-16 Polar, checking out if I want to go to the higher magnification.

 

[NateVA]

Well, there you have it.

1. I didn´t know about the Swaro FOV - thingy, I totally agree, that´s ridiculous.

2. Welly-well, my scope right now is the S&B 3-12x54 Polar, now you got me on that.
According to RUN8 it will be a huge downgrade in brightness, if I go with the S&B 3-18 Meta (zoom rate and objective diameter).

So I probably stick with it, or do make a comparison to the 4-16 Polar, checking out if I want to go to the higher magnification.

I regret that Swaro makes great binoculars and spotting scopes (my binos are EL 10x50) but it's extremely easy to avoid their riflescopes given their reputation for bad reliability.

 

[davsco]

The exit pupil is the width of the beam of light leaving the eyepiece, usually measured in millimeters (mm). The larger the exit pupil, the brighter the image will be under low-light conditions. Exit pupil size is calculated by dividing the objective lens size by the magnification power.

i don't think it's the 'times zoom' or zoom range that necessarily affects brightness, but more the magnification settings vs the objective diameter. for instance, a 1-10x50 (10x zoom) at 10x will have roughly the same brightness as a 2.5-10x50 (4x zoom) also at 10x. and the same should be true with both of them at 2.5x. and the 10x scope at 1x will be brighter than the 4x scope at 2.5x.

 

[Makinchips208]

A 42mm Objective gives you 1385.4 square mm of lens, and a 56mm gives you 2463 square mm. So the 56mm has a 78% larger lens area to transmit light.

But that does not mean you get 78% more light or 78% brighter image with both scopes at the same magnification.

 

[NateVA]

The exit pupil is the width of the beam of light leaving the eyepiece, usually measured in millimeters (mm). The larger the exit pupil, the brighter the image will be under low-light conditions

I recently watched this video below (around the 13:25 mark he mentions objective diameter) and it kind of threw me off. @koshkin does the exit pupil affect how we perceive the light on our eyeball or does it actually improve the light transmission? Not sure where the lens coatings and all that come into the equation.

 

[RUN8]

But that does not mean you get 78% more light or 78% brighter image with both scopes at the same magnification.

By exact percentage maybe not, but the 56mm is going to transmit more light at every magnification that the two scopes share.

Whether your eye is capable of utilizing it is another matter.

It’s a magnified optical system, bigger is better for transmitting as much light as possible. Rifle scopes or telescopes for looking at the heavens, same rules apply.

 

[RUN8]

Uhhhh a larger objective lens or mirror serves the same function in a rifle scope as a telescope. The exit pupil pretty well tells the tale, bigger = brighter and better resolution. Image brightness and resolution go hand in hand.

I don’t know why this concept is so hard for you to comprehend but bigger objective lens/mirror optical systems are always capable of transmitting more light than a smaller lens or mirror given roughly equal optical quality and lens coatings. It doesn’t matter very much that erector lenses are smaller than the objective lens in a rifle scope, exit pupil still comes out to objective lens diameter divided by the magnification. The angled mirrors in a Newtonian reflector that send light from the main mirror to the eyepiece on a telescope are much smaller than the main mirror, that doesn’t limit a 14” aperture mirror to being no brighter than a 10” mirror.

Do you think scope manufacturers just make large objective lens scopes because it’s fun and shooters like to deal with more weight? Same for people that buy telescopes and binoculars?

 

[NateVA]

Uhhhh a larger objective lens or mirror serves the same function in a rifle scope as a telescope. The exit pupil pretty well tells the tale, bigger = brighter and better resolution.

I'm not making any big declarations either way. I asked you why the guy who designs scopes for Leupold says a bigger objective doesn't mean it's actually brighter (same with bigger tube diameter). I don't know the answer to the question but there has to be SOME reason he's saying it right?