Light Transmission * Objective Lens = ???

[Ken Swenson]

After reading reviews of the Swarovski NL 12's being just as bright as the EL 12's in light light conditions, I opened my own can of worms in an attempt to quantify this qualitative, subjective claim.

In a nutshell, here is my question: Are light transmission and objective lens diameter multiplicative in nature?

Light transmission * objective lens = perceived brightness?

If so, I would take the NL light transmission of 91% multiplied by the objective lens diameter, then vice versa for the EL (assuming the same zoom range of 12x):

NL: .91 * 42 = 38
EL: .90 * 50 = 45

This would suggest significantly brighter views through the EL. I'm not hearing anybody claim this. Any other factors I might be missing?

 

[hereinaz]

The “light gathering” can’t be defined like that. You are getting into thoughts that aren’t relating how the optical system works. I don’t know much, but that I know…

There isn’t more light because of magnification, because the field of view shrinks. Think about it like this, the light transmitted by a 12x or 8x still has the same percent of light transmitted through the glass.

The higher 12 mag magnifies more light from a smaller area (small field of view) but it is similar in total brightness as a 8x magnifying more area (large field of view)

Ultimately, the light has to get compressed into the same “exit pupil” to enter through your eye pupil and land the image on your retina.

Optics companies manage a balance between field of view, exit pupil size, magnification, and other stuff.

The NL probably have some different balance in field of view or something.

In the balance, there won’t really be an appreciable difference in compatible optic systems that choose the optimal balance between the above.

NL might be as bright, but there is something else about the design parameters besides objective size.

Is is field of view difference?

In the end, it is way more complex than any internet discussion I could have, or have seen in forum. And, I probably am wrong on some points. But, the above serves me enough to say, it’s above our pay grade.

Select for magnification and field of view, that’s the material difference.

 

[JohnJohnson]

I've been trying to figure this out too for rifle scopes. I'm toying with the idea of just ponying up the $8 to subscribe to the DLO site to read the articles and watch the videos explaining this stuff. My main loose end is I need to figure out if there are meaningful differences in how rifle scopes, binoculars, and spotting scopes transmit light. I'll paste a quote from DLO below on light transmission in rifle scopes, so not exactly what you're asking about but the last line may be relevant.

"With modern scopes, light transmission is not indicative of low light performance. They are all quite good and your eye can not really tell the difference between 95% and 85%. Light transmission value kinda tells you how good the coatings are and is often a good predictor of stray flare suppression. Apparent brightness of the image in low light mostly depends on image fidelity and contrast (one of the reasons Leica Magnus does so well)."

So if I interpret it correctly, it sounds like the superior contrast and coatings of the NL make it regain the ground it lost from having a smaller exit pupil.

 

[roweraay]

In bright light conditions, you will not see any difference other than the quality of the optics, as long as the exit pupil is at least 3mm in size (pretty much 3mm is all you can USE, in bright light and an exit pupil that is larger than that, will just be extraneous - in BRIGHT light conditions). The quality of the NL optics are certainly a notch about the EL, and that’s what you see.

The EL 12s, with its 50mm objectives, WILL be brighter in extremely low light conditions, than the NL 12s. The smaller exit pupil of the NLs simply cannot avoid physics, when the light levels are low, since in low light, the 3.xmm exit pupil of the NL 12s will become a limitation, while the 4.xmm exit pupil of the EL 12s is letting in more USABLE light.

 

[hereinaz]

I've been trying to figure this out too for rifle scopes. I'm toying with the idea of just ponying up the $8 to subscribe to the DLO site to read the articles and watch the videos explaining this stuff. My main loose end is I need to figure out if there are meaningful differences in how rifle scopes, binoculars, and spotting scopes transmit light. I'll paste a quote from DLO below on light transmission in rifle scopes, so not exactly what you're asking about but the last line may be relevant.

"With modern scopes, light transmission is not indicative of low light performance. They are all quite good and your eye can not really tell the difference between 95% and 85%. Light transmission value kinda tells you how good the coatings are and is often a good predictor of stray flare suppression. Apparent brightness of the image in low light mostly depends on image fidelity and contrast (one of the reasons Leica Magnus does so well)."

So if I interpret it correctly, it sounds like the superior contrast and coatings of the NL make it regain the ground it lost from having a smaller exit pupil.

Here is a podcast with an engineer from Leupold talking about this in riflescopes. It’s in the last part.

 

[JohnJohnson]

Here is a podcast with an engineer from Leupold talking about this in riflescopes. It’s in the last part.

The same Leupold guy did a nice explainer on rifle scopes with LRWTL as well.

 

[hereinaz]

In bright light conditions, you will not see any difference other than the quality of the optics, as long as the exit pupil is at least 3mm in size (pretty much 3mm is all you can USE, in bright light and an exit pupil that is larger than that, will just be extraneous - in BRIGHT light conditions). The quality of the NL optics are certainly a notch about the EL, and that’s what you see.

The EL 12s, with its 50mm objectives, WILL be brighter in extremely low light conditions, than the NL 12s. The smaller exit pupil of the NLs simply cannot avoid physics, when the light levels are low, since in low light, the 3.xmm exit pupil of the NL 12s will become a limitation, while the 4.xmm exit pupil of the EL 12s is letting in more USABLE light.

The benefit in low light is partly because the eye's iris also opens larger so that it can take in the extra 1.xx mm of the larger exit pupil?

 

[JGRaider]

We can read, listen, massage, etc every piece of information available, but the only way to know is to use them yourself. Ergonomics, how the fit your face, etc are a really big deal along with pure optical performance. Amongst the absolute top end glass, your just nitpicking to find a difference, and unless you have them side by side at the same time you'll never notice them. Even then the differences will be miniscule.

 

[Ken Swenson]

We can read, listen, massage, etc every piece of information available, but the only way to know is to use them yourself. Ergonomics, how the fit your face, etc are a really big deal along with pure optical performance. Amongst the absolute top end glass, your just nitpicking to find a difference, and unless you have them side by side at the same time you'll never notice them. Even then the differences will be miniscule.

That will always be the optimal comparison. My question was whether or not an objective measure could be used to determine any difference in performance until I'm able to rent both and look in low light. Sounds like the answer is no.

 

[Axlrod]

In bright light conditions, you will not see any difference other than the quality of the optics, as long as the exit pupil is at least 3mm in size (pretty much 3mm is all you can USE, in bright light and an exit pupil that is larger than that, will just be extraneous - in BRIGHT light conditions). The quality of the NL optics are certainly a notch about the EL, and that’s what you see.

The EL 12s, with its 50mm objectives, WILL be brighter in extremely low light conditions, than the NL 12s. The smaller exit pupil of the NLs simply cannot avoid physics, when the light levels are low, since in low light, the 3.xmm exit pupil of the NL 12s will become a limitation, while the 4.xmm exit pupil of the EL 12s is letting in more USABLE light.

I have compared both in low light and the NL's are a touch brighter than the EL's to my eyes.

 

[roweraay]

I have compared both in low light and the NL's are a touch brighter than the EL's to my eyes.

It is physically not possible. The only caveat would be if say a person has pupils that don't dilate beyond 3.x mm, even when the light is low.

The NL 12s have several advantages, including a larger FOV, and fantastic optics. But low light performance is certainly not one of them, vis-a-vis the EL 12x50.

 

[Axlrod]

It is physically not possible. The only caveat would be if say a person has pupils that don't dilate beyond 3.x mm, even when the light is low.

The NL 12s have several advantages, including a larger FOV, and fantastic optics. But low light performance is certainly not one of them, vis-a-vis the EL 12x50.

I'm just going off what I can see. Also had 3 others at the same time comparing them, all thought the NL's were better, including the owner of the EL's. That guy bought NL's to replace his EL's

 

[roweraay]

I'm just going off what I can see. Also had 3 others at the same time comparing them, all thought the NL's were better, including the owner of the EL's. That guy bought NL's to replace his EL's

I don’t have first hand experience with the EL 12x50. I did however have the NL 12s at one point. And have the fantastic NL 8s now.

Going by the published numbers, EL has 90% light transmission, while the NL has 91% light transmission. A relative wash.

The EL, with it‘s 4.2mm exit pupil size, has a 20% larger diameter, than the NL 12s with their 3.5mm exit pupil. That’s 56% MORE light let in by the EL 12x50, vis-a-vis the NL 12x42.

That should be a significant and noticeable difference, going purely by the numbers. Again, I don’t have any first hand experience in the field, with the EL 12x50s.

 

[roweraay]

Of course the performance of the bino could be more than what the numbers suggest. For instance, I have noticed that the sheer resolving power of my NL 8s, allows me to differentiate things that were togher to do even with some high quality 10x42s.

So the quality of the optics is certainly an element that’s not captured in the published numbers. Maybe those aspects are what the folks noticed between the EL 12s and the NL 12s.

 

[WannaBeRambo]

Things like Schott glass do make a difference, it has fewer microscopic bubbles in the glass, thus less distortion And better light transmission.
I’ve learned it’s the optics proprietary coatings that have the biggest impact on overall image quality, assuming the glass is similarly high quality. You really can’t get that from any literature, you must put your eyeballs up to it In the real world you plan to hunt.

So If you are going to “go big” on some nice glass pick some suitable candidates, then call the seller and work it out to have get them ship 3-4 comparable optics you think would be suitable and do a side-by-side comparison in the field. I did this and it was well worth the cost and effort.

You cannot mount the scope and of course, any marks or damage may mean you might get stuck buying that one, and you are likely responsible for return shipping and any insurance, but the extra $100 or so is offset by eliminating the nagging ”did I really buy the best one” post-purchase anxieties.

Swarovski has some good blogs on criteria to use.