Transmission, contrast and colour bias (2 Viewers)

[looksharp65]

First of all, I'd like to tell that this thread is a follow-up on my recent thread with the very intriguing (NOT!) title ”Comparing three 32 mm binoculars” which (as usual!) evolved into some more general issues around contrast, brightness and colour rendition.

http://www.birdforum.net/showthread.php?t=233869

Since this thread will contain some references to what's written in that thread, I recommend the reader to read through it and take a glance at the pictures.
I'd also like to apologize in advance for some possible occurrences of abusing the English language and for being sesquipedalian.

The topic, or rather the cluster of related topics, has been up to discussion more times than anyone here could count, even less read and digest. Perhaps I'm knocking at doors that have been open for years, but there seems to flourish much confusion and divergent opinions.
Hopefully I'll be able to shed some light on the subject, as a layman to other laymen.

 

[looksharp65]

All right, let's start! Here are the basic matters:

I. The technical issues and shortcomings of light-refracting instruments

Any optical instrument containing lenses, mirrors and/or prisms will inevitably modify the qualities and the amount of the light passing through it. In the ideal world, optical aberrations and light loss would be nil, so that the instrument would present a totally uninfluenced image just like it was made of pure air. In this thread, I will leave out optical aberrations and concentrate on light transmission as a whole and for different wavelengths.

II. The ability of the human brain to interpret the input it receives from the eyes in terms of brightness and colour bias.

Generally, this ability makes us more forgiving about colour rendition, but will inevitably add to the confusion because obvious variations tend to appear less obvious, and small variations will not reach the threshold level of the conscious visual sense.

III. The influence of the external circumstances while using binoculars
e.g. the colour temperature of the incident light and the reflection properties of the surfaces it illuminates.


CREDO:

1) No purely optical device will amplify any part of, or all of the light passing through it.
Any such perception is not in accordance with reality and is entirely emanating from the brain's ability to adapt to the sensations delivered by the eyes.

2) A moderate colour bias may support the eye-brain system's ability to discern details, however never without any disadvantage.

 

[looksharp65]

And now for the more detailed discussion. I'll start with ”Basic matter” # I.

The fact that a binocular only can subtract light, not amplify it, means that its colour bias shows that it subtracts less of that specific colour and relatively more of the other wavelengths. So if the colour bias is bluish, it absorbs more of the red, yellow and (partially) green wavelengths and less of the blue. This can happen as a result from the type of glass used in it, but today it most certainly emanates from the residual reflection not being processed by the antireflective coatings of the lenses. And conversely, the wavelengths not being as efficiently reflected in the prism coatings will fade out from the light bundle.

A binocular which has all its lenses antireflective coated with a strong green residual reflex will most certainly tend to have a colour bias that goes towards red/purple, especially if the prisms are silver-coated. This seems to be the case with the Bushnell Excursion 8x28, for example.

It appears that the current technology does not allow 100% transmission through the entire visual spectrum. Since the eye/brain system automatically corrects for this, no real damage is done to the brightness of the image.
What is somewhat more cumbersome, is that current technology seemingly does not allow an absolutely straight transmission curve. Looking at allbino's transmission curves, the Swarovisions seem to come quite close, but lose some transmission at both the dark blue and the red end of the spectrum. The Nikon EDG has a weak bias towards red, but seems to cover the human eye's sensitivity range just a little better.

 

[looksharp65]

Basic matter #2

If we were glassing all the day, without putting the binoculars down for a mere second, the perceived colour bias of the binoculars would seem natural, but since we compare the scene against what we see with the naked eyes, we will always be able to note some deviation. The same goes for their brightness in general.
Different individuals are likely to have slightly different proportions of the types of rods used for the colour sense. This basic configuration may have an effect on how small colour biases are perceived by the individual, but is by its subjective nature unmeasurable.
But a colour bias that by the brain is being adjusted to how it subjectively means that things should look, will not change facts. If the binocular absorbs too much blue light, then the blue light is gone.
If compared to a more colour-neutral binocular, the loss will show as a reduced brightness in part of the image.

 

[looksharp65]

Basic matter #3/Credo #2

The light environment in which we use binoculars is of special interest as different transmission properties will tackle different situations in either a good or a less-than-desirable way.
Let's mention high contrast scenes for example. Over the illuminated parts of the image, the incident light flows freely and is partially absorbed, partially reflected from the various surfaces we look at. But the parts of the image that don't receive direct sunlight are only illuminated by scattered light, light that has already been reflected from other surfaces, and maybe also from sunlight being filtered through foliage. Since the colour temperature of this light is much cooler/bluer than the incident light, this scene benefits from an enhanced transmission of blue light.
In this particular case, an extremely high transmission of all wavelengths will not be enough since the eye's pupil will constrict in order to adapt to the brightness of the image.
But a blue/green bias will emphasize the shaded parts of the image and show what's in there. This will occur on the expense of colour contrast, since the warmer colurs (yellow, orange and red) will fade by quite a bit. This is what the Zeiss FL does – it has a very high transmission, but that also peaks around the same level as the human eye's sensitivity maximum, thus reinforcing the already existing ”bias” of the visual sense rather than stay neutral.
A binocular like this handles contrast very well.

There can also be occasions where a reduction of the transmission of blue light is desirable.
In general, suppression of blue light increases contrast, which is a distinct disadvantage compared to the previous case. However, it is beneficial for discrimination of fine hues. The relative absence of blue will reduce the total amount of light transmitted, thus allowing the eye's pupil (or the camera's diaphragm, for that matter) to dilate. The generally brighter rendition of green, yellow and red will increase the colour contrast of various brown hues very nicely.
On overcast days, when the contrast is less pronounciated, the difference against a ”cooler” binocular can be slightly smaller, and it will help reduce the overall bluish cast under the clouds.
A binocular like this reproduces or shows contrast very well.

Even on bright days at the sea, ”warmer” binoculars could be less tiring thanks to their ability to reduce blue light. However, in back-lighting, watching birds on the sea, a ”cool” binocular would be better again.

 

[looksharp65]

Conclusion

- The colour bias of a binocular is a function of its disability to transmit 100% of the light entering.

- The brain can adapt to make the colour bias seem fairly neutral, especially after prolonged use, but the transmission loss will either make colours look slightly faded or reduce brightness of shaded parts of the image.

- A high and flat transmission curve is desirable compared to a peaked or sloped one even if they can seem equally colour-neutral, but binoculars with a distinctive colour bias can, while less allround, often offer significant advantages over non-biased ones.

 

[looksharp65]

Teaser

It is my firm belief that it is quite common that the two eyes of an individual don't have exactly the same colour bias, and that this ostensive anomaly in fact is part of the brain's exquisite ability to discern hues. Somewhat reminiscent of what a HDR camera does with bracketed exposures, the brain will merge the two images and get ”the best of two worlds”.
I believe that this difference can be enhanced and/or produced if not obviously there. I would like to see a binocular with different colour bias in the two barrels, and I'm confident that the brain would pick the best from the scene.
Expecting such a device to enter the market is overly naive, but the second best solution would be to add a weak filter to one of the barrels. The Swarovision would benefit from some orange on one side, and the EDG from some blue. This, by the way, would be quite easy, I guess a blue visibility tinted contact lens would be enough.

 

[NDhunter]

LS:

Interesting your post, but on the previous thread, and now, I have an issue with
anyone judging any color cast or preference of any optic when using a contact lens, as you have mentioned you use some with a tint.

I do realize you sell contact lenses, and can play around with tint colors.

That does confuse those looking for optics advice.

Not sure you know this one, but there is a story about looking at the world through
rose colored glasses may apply here.

Your last post does lead me to post, don't mess with the Swarovision or the EDG, they are just fine as they are.

Jerry

 

[looksharp65]

Jerry, I'm not here as a contact lens seller. Furthermore, nearly all "ordinary" contact lenses are visibility tinted, and the use of contact lenses is very common in the US, and fairly common in Sweden.
The point in the other thread was that the combination of my eyeglass lenses and the HG pushed the color bias above a threshold, but when using contact lenses that didn't happen, which was quite strange since my colour perception should be adapted to the visibility tint of the CL, and then the image through the HG would still look more red than "IRL". This didn't happen.
My spectacle lenses are of course multicoated, and their residual reflection is medium strong green. As high-index organic lenses, they are not perfectly colour neutral, but I never see that in ordinary use.


And, of course I know that your top binos are close to perfect. Judging from my experiences from the FL and the HG, I think I'd prefer the EDG.


Regards

//L

 

[NDhunter]

LS:

I think I do understand your observations.

What is important here, is the top mfrs. are well aware of how any color bias is
reflected in their optics. And for 99% of users, it will not make not a bit of difference
in their use, or buying decision. It will be other factors, ergos, warranty,price, etc.

The issue that I have is how you have related your spectacle and contact usage,
and how that is important.

For me, I do not want anything like that, to have any place in comparing optical
differences. "Rose Colored Glasses".

Jerry

 

[newfie ghost]

Teaser

It is my firm belief that it is quite common that the two eyes of an individual don't have exactly the same colour bias, and that this ostensive anomaly in fact is part of the brain's exquisite ability to discern hues. Somewhat reminiscent of what a HDR camera does with bracketed exposures, the brain will merge the two images and get ”the best of two worlds”.
I believe that this difference can be enhanced and/or produced if not obviously there. I would like to see a binocular with different colour bias in the two barrels, and I'm confident that the brain would pick the best from the scene.
Expecting such a device to enter the market is overly naive, but the second best solution would be to add a weak filter to one of the barrels. The Swarovision would benefit from some orange on one side, and the EDG from some blue. This, by the way, would be quite easy, I guess a blue visibility tinted contact lens would be enough.

This is a good point, not only do people see differently, sometimes our own eyes differ. I never noticed this until I bought a spotting scope. My right eye can see better contrast and see richer color than my left. It is also sharper. The differences are small but they are real irrespective of corrective lenses. With both eyes open I can't detect the difference as the brain corrects for it in the unified image.

Keep both eyes open and switch back and forth from one eye to the next on a good spotting scope. You might notice the difference in one of your eyes in terms of color and contrast.

 

[ceasar]

I noticed this difference in color perception between my eyes years ago. It is most apparent to me in the fall when the trees are changing colors. This time of the year, when everything is various shades of green or gray in the trees in my area, I do not notice it at all.

I have primarily used Nikons over the years and now I wonder if their color bias might contribute to how I see the fall colors.

Bob

 

[looksharp65]

LS:

The issue that I have is how you have related your spectacle and contact usage,
and how that is important.

For me, I do not want anything like that, to have any place in comparing optical
differences. "Rose Colored Glasses".

Jerry

Jerry, to be honest I don't understand why this is an issue to you. The examples I mentioned show the influence that visual correction will have on the colour representation, and how this influence with some astuteness can be turned into an advantage.

Whether we like it or not, whether we personally need it or not, the use of spectacles and contacts is an urgent need to several tens of millions of people only in the US.

For people with astigmatism, even mild such, not making use of spectacles/CL results in sub-par resolution capability.
And if resolution is impaired, the need for sharp binoculars is nonexistent.
A user with a low visual acuity can only make use of the magnification, which can be had with sub-par or even faulty binoculars.

If we're only after assessing transmission curves, any human would be the worst possible device to perform the task. The great deal of subjectivity involved in such an assessment will make the result notoriously corrupt. But since spectacles or CL inevitably will add their touch to the perceived colour balance in real use, they just cannot be excluded from the evaluation. After all, we are talking about binoculars as devices that are intended to be used by humans, aren't we?

So, let me congratulate you for having a perfect vision and for owning the two best binoculars on the current market. However, don't imagine you're the norm, you're but a fortunate exception.

Regards,

//L

 

[typo]

Lars,

Thanks for a very interesting summary.

As I understand it we are able to discriminate colour best under while light; usually considered to be about 5500k colour temperature. In practice daylight may be shifted into the blue on overcast days for example or red at sunset, impairing our colour judgement. It's illustrated in this paper in figures 2 and 3.
http://chemeducator.org/sbibs/samples/spapers/34samplejg.htm

In the UK we get a lot of overcast days and I generally find that the colours through a slightly warmer biased binocular are give 'nicer' colours much of the time compared to more neutral pairs. My more neutral pairs may be a bit better at sunset, (but they can be improved with a light blue filter). All this would seem to make sense as it would push the spectrum reaching the eye towards a 'white' profile. Of course, it results in a reduction in the total amount of light reaching the eye, but isn't that what pupil dilation's for?

Of course when light levels are really low then any loss in transmitted light is detrimental. At the moment the only practical answer I have is to use different pairs for different light conditions. I've suggested before that using filters might be a practical way to resolve this. At the moment Kowa has the only roof bino I'm aware of that is designed for this.

David

 

[Arek]

Some practical info in this interesting topic:
http://www.allbinos.com/160.1-article-Colour_rendering_in_binoculars_and_lenses.html

 

[looksharp65]

Arek, thank you for the link and for fortyfying my thread with some more technical aspects of the coating technology.
I should hasten to add that there are a handful of different coating technologies and they will work in different ways.
I have been told by a representative at the Rodenstock facilities in Münich that the residual reflection can be made colourless. I don't know whether this really is the truth and I also expect that the glass/plastic quality in terms of refractive index will be very important. Furthermore, he claimed that it was marketing considerations that made them go for a green residual reflex. It clearly shows there is something "different" compared to uncoated lenses, which will increase the perceived value of the coating.

Considering the large number of surfaces in today's top binoculars, I still think the transmission curves could become less sloped and wider than in the state-of-the-art binos of today. It's about choosing the exact refractive index for every glass element and coat it with the most appropriate AR coating for every single lens.
Then again, I still believe that the "HDR" idea of slightly different transmission profiles for the two barrels could work as well, or maybe even better.

David, even here we have very many overcast days, and I can follow your line of reasoning. There is no evidence that the warm colour bias would be a general disadvantage, but, like you say, having different bins means that the more suitable pair can be chosen for every particular birding situation.
Thanks for the link!

//L

 

[looksharp65]

Update:

First serious try-out with one slight blue contact lens seems very promising with a visible enhancement of detail discrimination in shaded parts with the HG.
I have ordered an 82 A blue filter that will be tried on the left barrel, since my left eye has the warmer color bias.
If it all works fine, I'll try an 81 A on the Zeiss FL's right barrel too.

//L

 

[typo]

Must admit I hadn't considered different colours for each eye. I think my colour vision is symmetrical as far as I can tell. Look forward to the results with interest.

You may have found this already but here's a list of transmission data for all the Wratten series.
http://www.hbcpnetbase.com/pdf/19_54.pdf

David

 

[looksharp65]

Thanks David!

In fact, I hadn't seen it and the transmission tables for the 82A and 81A show a considerable decrease of light transmission even for the wavelengths that are least affected.
I figure the results are reliable but measured through gelatine filters mounted between 2 glass pieces, that are not AR coated.
The necessary exposure compensation when using an 82A multicoated glass filter is 1/3 f/stop, which I believe should translate to 16.7% absorption across the entire range of wavelengths. (An exposure difference of 1 EV means that the brightness is reduced by 50%). I might be wrong here, though.

//L

 

[typo]

But it will probably look brighter with the 81A.

David