Effect of Higher Overall Transmission During Daylight Use (1 Viewer)

[Maljunulo]

Not all the light which enters the objectives of a binocular emerges from the eyepieces.

Some of it is scattered, and some is absorbed. That light which is absorbed, effectively ceases to exist.

Light which is scattered degrades the image, and reduces its contrast. (I believe)

Therefore, I do not believe that higher light transmission is irrelevant during bright daylight use, as seems to be a belief shared by some.

At this point I will have to descend into hand-waving, because I lack the background to make a sound argument.

I believe a higher-transmission binocular will present a more faithful image of the object, than a lower transmission glass.

The greater the percentage of the light, sampled from the object, and assembled into an image, the "better" that image will be.


Thoughts?

 

[Rg548]

Higher transmission i believe does make a difference on any given day, whereas exit pupil may not, depending on the light levels and operators pupil performance.
That's what I think, although if it's wrong.... we will soon find out

 

[Binastro]

The light doesn't cease to exist, it is probably changed into heat.

A very high transmission binocular may be too bright in bright sunshine, and the actual image may degrade rather than improve.

There are too many variables here to give one answer.

Glare is a major problem, and not all high transmission binoculars are immune to glare.

This question reminds me of 'What is the best binocular?'
There is no answer to this.

Regards,
B.

 

[GrampaTom]

Thoughts?

I too wonder.. and have no expertise. Can we guess this question comes from your recent 8x30 Habicht with 96% vs your SF 8x32 at 90 and how you've been experiencing it?

 

[William Lewis]

Go on then. I'd rather use a binocular with a bright image than one with a dim image. To a degree it's personal preference but no one wants a really dim view, it's like zooming your scope up to 60x, different mechanism, similar outcome - you'd rather have the same bright view you get at 20x but 60x closer.

Another thing to consider is contrast, dark Vs light for example. If you have a lower transmission it will be dark Vs not quite so dark. Even 100% transmission isn't going to transmit or brighten darkness so it never gets to the point of a view being washed out like an over exposed photo.

Also your never going to get a view through binoculars that is brighter than naked eye, despite "image intensifier" claims- you might get more detail at range say 10x - that's what binoculars do but it won't be as much detail or as bright as if you stood 10x closer.

So, as usual, all else being equal id rather have higher transmission....

 

[agus_m]

A very high transmission binocular may be too bright in bright sunshine, and the actual image may degrade rather than improve.

I wonder what you mean with this. I think it is quite the opposite, you want the highest transmission possible, for the reasons that OP mentioned. I don't think it can be "too bright", it is never going to be brighter than what you see with naked eyes.

 

[Maljunulo]

I too wonder.. and have no expertise. Can we guess this question comes from your recent 8x30 Habicht with 96% vs your SF 8x32 at 90 and how you've been experiencing it?

No, as a result of reading a published statement that it is irrelevant, which got me to thinking. (although I can’t say that the Habicht didn’t contribute to keeping the wheels turning)

Obviously, I disagree.

 

[wllmspd]

I hope you have young eyes that themselves done have defects and scatter in or you might not get the best of the light the bino provides. The view between a Nikon 8x30E and E2 (when I owned both) was noticeable in brightness, but I am sure that if I only have one I would not have been unhappy with the dimmer view. I still really enjoy the view through my old 7x35 binos, with old coatings I’d hate to think what thier transmission is. If it gets dark I’ll just pull the 7x50 out. As noted the quality of the optics and the baffling is probably more important that raw transmission, I am sure you’d need a good few % difference to be visually noticeable.

Peter

 

[Maljunulo]

My eyes were “rebuilt” in 2008, when I had bilateral cataract surgery, with lens implants.

My retinas are OEM.

My experiences and what I see are irrelevant to the topic.

 

[Binastro]

Post #6.

The view with the naked eyes in bright sunshine is sometimes too bright.

That is why people use sunglasses.

Similarly, the view through high transmission optics is also sometimes too bright.

And if the image is too bright both the resolution and comfort is adversely affected.

There is a range of brightness levels that the human eye can cope with or feel comfortable with.

Even the full Moon can be too bright.
The albedo of the full Moon is only about 12% or 14%.

Venus albedo is very high.
It is best viewed in twilight.

Some military binoculars were provided with various filters on a filter wheel, including coloured and neutral density filters.

The fact that with ordinary optics the surface brightness can never be higher than with the naked eyes is a red herring in this context.

Although with electronic and image intensifier eyepieces this doesn't apply.

B.

 

[Binastro]

Post #9.

The experiences of the eyes are certainly relevant.

They are the sensors.

It is only in the context of what the eyes see that this subject makes any sense.

B.

 

[Maljunulo]

I’m discussing the image, not the eyes or brain used to look at the image.

Image “a” can be more or less bright than image “b” no matter who looks at them, or if no one looks at them.

 

[tenex]

Binastro is answering the question too well; a naive person might expect the thread to end here. But they never do.

Others here have been known to dream up simple theories of why they find their recently purchased binocular so fantastic...

(Edit: it is surely true historically that transmission loss has been mostly due to reflection/scatter, not absorption. But an expert would need to weigh in on whether that's still true at this point, and what impact if any that can have on image quality.)

 

[Swedpat]

A higher transmission not only increases the light reaching the eye, but also helps to increase contrast. This because light reflexions in the optical system decreases the contrast, and as more you can decrease these the better contrast. Just an example, there are differences between different coatings even when light transmission is the same.
If I am right, a prism binocular without any coating at all can lose almost half of the light because of the internal reflexions.
So while an uncoated 7x50 still can be brighter than a 7x35 with the best coating, the contrast and colors will be really bad.
In this case the 7x35 will probably outperform the 7x50 even in the dimmest conditions because the much better contrast will help detecting more details.

 

[GrampaTom]

Twilight Factor
"Twilight factor is a theoretical estimation of how much detail can be seen in low light and is estimated by first multiplying the magnification by the objective lens size, and then taking the square root of that product. So twilight factor can increase with an increase of either magnification and objective lens size or both. The twilight factor can also remain the same if the magnification is doubled, but the objective size is cut in half (and vice versa). For example, the 8 X 50 binoculars would be 8 times 50 =400, then the square root of 500 = 20.0 value for twilight factor. The twilight factor for the 10 X 50 is simply 10 times 50 = 500 and the square root of 500 = 22.4, so the 10 X 50s have a 12% detail advantage over the 8 X 50s in low light."

​

​

This from Zeiss, themselves here, (note the criticism para below): ​

Twilight factor - ZEISS Hunting

The twilight factor is often referred to as a comparative value for the suitability of binoculars when less light is available. Learn more.

blogs.zeiss.com

​

"Twilight factor​

• Night Hunting
• Tech Know-How

What does it mean?​

The larger the entrance aperture the more light that enters the binoculars. And the higher the magnification at the same image brightness the more details that can be observed. The twilight factor is often referred to as a comparative value for the suitability of binoculars when less light is available.

Definition​

It is calculated by multiplying the lens diameter by the magnification and obtaining the square root from the result:

Criticism on the twilight factor​

However, this twilight factor is a mere mathematical parameter. The really important performance data of binoculars (image quality, contrast, transmission, color rendition etc.) are not taken into consideration. Every pair of 8 x 42 binoculars, for example, has the same twilight factor – 18.2 – regardless of how good or bad it is in practice, regardless of the brand or price! The twilight factor can also be completely misleading as shown in the following example: two binoculars, 8 x 56 and 56 x 8 (such a model does not exist but would be feasible theoretically), have the identical twilight factor of 21.2! While an 8 x 56 model is ideal during twilight, a 56 x 8 pair would e totally unusable – even during the day.

Practical tip: Exit pupil​

The twilight factor alone does not permit any kind of real statement. A correspondingly large exit pupil is always decisive and important for twilight use. Ideally, it should be at least as large as the pupil of the user. Anything with an exit pupil smaller than 4 mm is, therefore, unsuitable in the waning light right from the start – even if the twilight factor is high."

 

[GrampaTom]

So, how should we think of the relationship of Transmission to Exit Pupil?

 

[Binocollector]

So, how should we think of the relationship of Transmission to Exit Pupil?

If I'm not completely off with my math.
A 7x40 with 60% transmission should still be 1.3x as bright as a 8x32 at 94% transmission as soon as the pupil of the observer reaches the size of the exit pupil.
7x40 has an EP of roughly 5.7mm.
Surface is r^2×pi = 102, with a 60% transmission (let's say an old military bino) we get 61.2.
8x32 - EP 4mm, surface 50.3 sq-mm. 50.3x.94=47.3.
47.3xX=61.2 - > X=61.2/47.3=1.3.
At least that's what I think. Might be wrong though. I guess we need @Holger Merlitz or any other expert on the forum.

 

[tenex]

Post #14 and its sequelae are (as so often) irrelevant repetitive distraction. The question was not about brightness or twilight performance.

High-quality bins today typically have 88% transmission or better, mainly through the use of improved coatings. The question is whether the remaining loss (4~12%) is still primarily due to internal reflection, or to absorption, and whether differences in this rather narrow range noticeably affect image quality (contrast etc).

 

[Jason Bugay Reyes]

Post #6.

The view with the naked eyes in bright sunshine is sometimes too bright.

That is why people use sunglasses.

Similarly, the view through high transmission optics is also sometimes too bright.

And if the image is too bright both the resolution and comfort is adversely affected.

There is a range of brightness levels that the human eye can cope with or feel comfortable with.

Even the full Moon can be too bright.
The albedo of the full Moon is only about 12% or 14%.

Venus albedo is very high.
It is best viewed in twilight.

Some military binoculars were provided with various filters on a filter wheel, including coloured and neutral density filters.

The fact that with ordinary optics the surface brightness can never be higher than with the naked eyes is a red herring in this context.

Although with electronic and image intensifier eyepieces this doesn't apply.

B.

Thanks a lot. I learnt something today

 

[GrampaTom]

Post #14 and its sequelae are (as so often) irrelevant repetitive distraction. The question was not about brightness or twilight performance.

High-quality bins today typically have 88% transmission or better, mainly through the use of improved coatings. The question is whether the remaining loss (4~12%) is still primarily due to internal reflection, or to absorption, and whether differences in this rather narrow range noticeably affect image quality (contrast etc).

Had to look that one up. Found this: Definition of SEQUELAE.

Im guessing your intent was to suggest that #14 and all that followed were, "irrelevant repetitive distractions." I'd point out #15 was a clear attempt to point out the problem with at least part of 14. Seems hardly an irrelevant distraction. I got that not only was the question not about twilight performance, but that theory itself has been discredited.