New but probably wrong insight about lowlight (1 Viewer)

[Jason Bugay Reyes]

So with the help of spotlight at nite and using 10x42 and 10x32 hand held for nocturnal wildlife, which one will resolve better details if the user is around 53 years old?

 

[Gijs van Ginkel]

This discussion comes back over and over . Therefore I decided to compose a large review paper entilted: "Color vision, brightness, resolution and contrast in binocular images". It is a 30 page review of published data with regard to this matter and it is published on the WEB-site of House of Outdoor. That may answer a lot of the questions raised.
Gijs van Ginkel

 

[Ignatius]

Thank you. Surprisingly, the paper is from 2013.

 

[Maljunulo]

So with the help of spotlight at nite and using 10x42 and 10x32 hand held for nocturnal wildlife, which one will resolve better details if the user is around 53 years old?

Even if I knew enough to take a shot at answering that, I wouldn’t.

Too many unknown and unknowable variables.

 

[Scott98]

So with the help of spotlight at nite and using 10x42 and 10x32 hand held for nocturnal wildlife, which one will resolve better details if the user is around 53 years old?

The 10x42.....I'd be careful with that spotlight nocturnal wildlife will be running away

 

[jan van daalen]

That is interesting. I didn't know that. What is the range of movement? Is that really as big as from 4.2 to 5mm and back, and than from 4.2 to 5mm again?

The range of movement is always the same. The pupil moves. It can be 3mm or 6mm in diameter. When it moves it moves regardless its diameter, something the Iris is responsible for.

 

[Ignatius]

Does that mean the pupil dilates and contracts or the pupil oscilates (as in nystagmus)?

 

[jan van daalen]

Does that mean the pupil dilates and contracts or the pupil oscilates (as in nystagmus)?

Regardless the size of the pupil, the pupil moves (the visible size of the pupil is decided by the Iris).
Otherwise we should only see the object straight ahead of the view.

 

[Ignatius]

Regardless the size of the pupil, the pupil moves (the visible size of the pupil is decided by the Iris).
Otherwise we should only see the object straight ahead of the view.

Aaah ... your eyes must be different from mine. My pupils do not move when I look around while keeping my head still - my whole eye(ball) moves. I did not know that pupils could move independently from the rest of the eye. Learn something every day.

 

[ReinierB]

Thanks for all the answers! I received the book, but haven't read it yet. So maybe I will get some answers while reading it.

But for now I still don't understand it totally what is wrong with the assumption I made and visualised in this picture. Can somebody explain what is wrong? Although Jan van Daalen already made a comment that the size of the pupil changes constantly (but up to 5.25mm?). However, is that the only reason this theory is wrong?

 

[Maljunulo]

I’m just curious why you want more than one reason.

I’m assuming we can define perceived brightness as “related to the number of photons falling on the retina at any given time”.

It seems obvious to me that this will vary as the pupil either expands or contracts.

The pupil contracts reflexively when the external light level increases, so this is going to have a profound effect on how bright the image appears to us.

The human eye is not a reliable photometer.

 

[Ignatius]

Maybe sometimes one can arrive at the same conclusion by different routes. Maybe some people need things explained in a certain way so they can understand them.
There are quite a few people here with profound knowledge of optics, physics, etc. Not everyone who wants to understand some of the topics on this board has such a background. And not everyone with such a background also has the didactic ability required to 'teach' the others.

 

[jan van daalen]

Aaah ... your eyes must be different from mine. My pupils do not move when I look around while keeping my head still - my whole eye(ball) moves. I did not know that pupils could move independently from the rest of the eye. Learn something every day.

You're quite right. The eyeball moves (so the pupil moves). Sorry for the confusion. I'm just Dutch.
The main point is that the exitpupil from the binocular does not move. So when the pupil (while moving) has the space of, for example, 7mm from a 10x70 but is by itself just 4mm it collects more light while in theory the 10x42 would do the same job as a 10x70.

 

[Binastro]

I think what is being discussed as brightness is in fact surface brightness.

The pupil size does oscillate slightly and is not constant in size.

The eye is a good photometer when it comes to comparing luminosity.
Accurate to about 9% or 10% with an experienced viewer, but not everybody has this ability.
It is a bad photometer in actual luminosity.

I find also that estimating AFOV by eye is poor in absolute terms with no comparison standard.

The two eyes may vary considerably in sensitivity to light, both day and night.

The original question is about low light.

Here lies the problem, as the amount of dark adaption varies. It also varies person to person, by age, by tiredness and the light levels experienced before low light vision and the time elapsed.

If one closes one eye and looks at a computer screen in a fairly dark room, then the difference in light levels and colour perception is amazing when the closed eye is open.
Say 5 to 10 minutes with one eye closed.

Transmission measurements give a fairly good idea of surface brightness.

There are too many variables to be definite but the surface brightness in an 8x42 is probably brighter than a 10x42 in birdwatching low light levels.

However, fainter stars are visible in the 10x42 unless the pupil size is particularly small.

Personally, I have always favoured a 10x50 instead of 7x50, although the latter can provide very relaxed viewing.

Regards,
B.

 

[agus_m]

View attachment 1573194
Thanks for all the answers! I received the book, but haven't read it yet. So maybe I will get some answers while reading it.

But for now I still don't understand it totally what is wrong with the assumption I made and visualised in this picture. Can somebody explain what is wrong? Although Jan van Daalen already made a comment that the size of the pupil changes constantly (but up to 5.25mm?). However, is that the only reason this theory is wrong?

I think the image is not wrong, but it would mean that if you look at a point source, in those circumstances (same eye's pupil size, and exit pupil of 8 mag bino too big compared to the eye) the point source would look brighter in the 10x bino. Now an extended image, say you look at the wall, would look the same brightness in both binos because, although the 10x bino gathers more light, it also magnifies and stretches the image comapred to the 8x.

 

[Swedpat]

This picture mixes up relative brightness with light amount.
The brightness is always primary based on the effective exit pupil.
With 4,2mm(or smaller) eye pupil, 8x42 and 10x42 provide equally bright image. As soon as eye pupil is larger than 4,2mm, 8x42 becomes brighter than 10x42.
But when observing a light source the light amount reaching the eye is higher with 10x42.
In order to receive the same light amount from a light source with 8x42 as with 10x42, eye pupil needs to be 5,25mm.

 

[NatureLover123]

If you take an image and magnify it by 2X, the area of the image is then four times what it was at 1X.

It cannot be as bright as it was at 1X, because it is the same quantity of light, but spread out over a larger area.

I don’t know any other way to say it.

Let‘s assume two binoculars of the same quality:
8x42
10x42

The 10x is only 20% dimmer and gives 25% more detail, as long as your eye pupil did not exceed 4.2mm.

Because of higher magnification the 10x is 56.25% dimmer as the 8x (quadratic effect), BUT the 10x concentrates the same incoming light (both are 42mm, also quadratic effect of the size of the aperture) across a smaller exit pupil, so there is an effect that the light is 25% more concentrated (brighter) for the 10x. Thats why the 10x is just 20% dimmer than the 8x of same quality, as long as your eyes pupil is not bigger than 4.2mm.

But the effect of 25% more detail of a 10x against an 8x is slightly more important at low light than a brighter image IMHO:
In low light your eyes are not resolving as good as at bright day. So a binocular that prefers detail over brightness is slightly better to actually see detail at all.

There are types of hunting where you hunt from a hide at close range, just a few meters (lets say 10-30 meters or so), then the detail you get from an 8x might be enough to see that animal but you might not be able to tell if it‘s a male or female or what age the animal has.

(I am not a hunter, I just did some math)

 

[Maljunulo]

Okay

 

[Elkhornsun]

Our eyes depend on contrast with subject detection and identification. With my photos I can "sharpen" them by simply increasing the amount of contrast. With lower light levels I can compensate in part by using a 10x binocular that provides 25% more image magnification than an 8x one. I have two sets of otherwise identical binoculars in 8x25 and 8x32 and 10x25 and 10x32 and have found myself using the 10x ones the most with the exception when I use a 12x50 binocular.

 

[Swedpat]

Let‘s assume two binoculars of the same quality:
8x42
10x42

The 10x is only 20% dimmer and gives 25% more detail, as long as your eye pupil did not exceed 4.2mm.

Because of higher magnification the 10x is 56.25% dimmer as the 8x (quadratic effect), BUT the 10x concentrates the same incoming light (both are 42mm, also quadratic effect of the size of the aperture) across a smaller exit pupil, so there is an effect that the light is 25% more concentrated (brighter) for the 10x. Thats why the 10x is just 20% dimmer than the 8x of same quality, as long as your eyes pupil is not bigger than 4.2mm.

But the effect of 25% more detail of a 10x against an 8x is slightly more important at low light than a brighter image IMHO:
In low light your eyes are not resolving as good as at bright day. So a binocular that prefers detail over brightness is slightly better to actually see detail at all.

There are types of hunting where you hunt from a hide at close range, just a few meters (lets say 10-30 meters or so), then the detail you get from an 8x might be enough to see that animal but you might not be able to tell if it‘s a male or female or what age the animal has.

(I am not a hunter, I just did some math)

I don't understand from where you get the idea that higher magnification concentrates the incoming light more.
The objective gathers the light and the gathered light is proportional to the area of the objective. The magnification determines how big area the light is spread out over.
If you double the magnification the apparant area of the observed object becomes four fold. The result of that is that the relative brightness becomes four times lower.
Relative brightness is proportional to the area of the exit pupil and magnification does not add anything to that. Providing light transmission is the same all configurations with same exit pupil have same brightness.
For example: whether you observe the moon at night with a 7x50 or 50x50 the total light from the moon reaching your eye is the same. With 50x the apparant area of the moon is 51 times larger than with 7x. But the light intensity is 51 times lower. There is no more concentrated light with higher magnification. It's more correct to say that the light is more concentrated with lower magnification.