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Brightness of 8x32 vs 10x42 (1 Viewer)

oso

Member
France
Hi
I'm new here, but I've been birding for 30 years in south of France, and other places in Europe; I think this is my first post here :)

I've been using a Leica Trinovid 8x20 since 1991, and I plan to by a good pair of brighter binos for more confortable observations at dawn or dusk (and increased FOV and confort by the way).

10x42 would be great (as complementary magnification to my 8x20), otherwise 8x32 are lighter (I live in the Alps).

So my very naive question: Is it reasonnable to expect the same brightness from both a 10*42 and a 8*32, all other parameters been equals (let's say Zeiss SF 8*32 vs SF 10*42, or Swarovski's equivalents, these models beeing in my scope).

thank you for your time
 

jring

Well-known member
Hi,

first of all, welcome to BF!

As a dedicated pair for observations at dawn or dusk, I would take a pair of 10x42 over an 8x32. Of course, if you are younger and your eyes pupils still open wide in bad light, a pair of 7x50, 8x56 or 10x70 would be best.

In general, the basic number to determine image brightness is the exit pupil, that is aperture divided by magnification. For 10x42 and 8x32 this is the same. But the absolute aperture and also the magnification have a lesser effect on low light optical performance, which bring the 10x42 pair in front.

Of course, the larger exit pupil of an 7x50 pair does not help a lot, if you eyes pupils only widen to 5.5mm or so in darkness... this can be measured by an eye doctor or optician... some here have done it themselves with a ruler and a digicam in front of a mirror... they'll probably chime in...

Joachim
 

oso

Member
France
Thank you Jring for this answer. i'm a young 51 teenager. Considering that both a 8*32 and a 10*42 will présent a 4mm exit pupil, one would expect the same level of brightness.
I was wondering whether other parameters would contradict what numbers suggest.
 
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qwerty5

Well-known member
United States
Thanks you Jring for this answer. i'm a young 51 teenager. Considering that both a 8*32 and a 10*42 will présent a 4mm exit pupil, one would expect the same level of brightness.
I was wondering whether other parameters would contradict what numbers suggest.
A 10x42 has a 4.2 mm exit pupil, also note what Joachim said: "the absolute aperture and also the magnification have a lesser effect on low light optical performance, which bring the 10x42 pair in front." Also, a larger objective will produce a better image with better control of aberrations.

I would recommend a 10x42 as the best compliment to your 8x20. If you were to get an 8x magnification, I would recommend an 8x42, since you already have a lightweight binocular, and the optical performance will be better than an 8x32.
 

jring

Well-known member
Next to the exit pupil light transmission is also an import factor for image brightness. Magnification is not a brightness indicator.
Gijs van Ginkel

Hi Gijs,

as for transmission - you are correct, I should have talked about that but didn't as the original post was trying to decide between an 8x32 SF and a 10x42 SF which I assume to be quite comparable in transmission.

Regarding magnification - sure, a higher magnification will not make the image brighter but in failing light of two instruments with equal brightness but different magnifications, the higher magnification one will make it easier to identify an object. That was what I meant with low light optical performance.

Joachim
 

oso

Member
France
Thank you all for your detailed responses! I feel that a 10x42 would certainly be a better complement as allround birding binoculars that can also be used in low light conditions.

Olivier
 

oso

Member
France
I just realized that thre is a mistake in the title of this thread: on should read "

"Brightness of 8x32 vs 10x42" instead of

"Brightness of 8x32 vs 10x32"​

Sorry:giggle:
 

Maljunulo

Well-known member
How many here truly believe they can see the difference between a 4 mm exit pupil and a 4.2 mm exit pupil,?

And we have to presume glass, optical train and coatings are identical, otherwise I believe the comparison is meaningless and futile, since all of those things affect the perceived brightness.

In my personal experience, my 8X32 SF in indeed "brighter" than my 2014 EL SV when compared while viewing the same object at the same time. (obviously alternately)

I think there are too many unknown and uncontrolled variables to permit any definitive answer in the "real world" as a general statement which would apply to all possible instruments.

I see much hand-waving and endless argument along the lines of the angels-on-the-point-of-a-pin type of discussion, and specifications being hurled like thunderbolts from Mt.Olympus.

(Just my view from a position of almost total ignorance.)
 

Gijs van Ginkel

Well-known member
Maljunulo, post 10,
This topic has been handled frequently on this forum, but I am happy to repeat it.
Brightness is determined by three factors; first of all the amount of light leaving the binoculars and that is determined by:
-1- the size of the exit pupil and
-2- the amount of light the optical system transmits.
Another factor is the color representation of the transmitted light since our eyes consider some colors brighter than others.
If I now look at the data we have obtained from the EL-SV 8x42 and the Victory SF 8x32 we see the following:
-a- the exit pupils are identical
-b- light transmission of the EL SV is over a broad range considerably higher then that of the Victory SF. Moreover the distribution of the transmitted light is for the EL-SV in favor of increased brightness observations.
My conclusion based purely on the measured data therefore is that the ELSV 8x32 shows greater brightness compared with the Victory SF 8x32.
I leave aside all personal properties of eyes, since that can differso much between different persons.
Gijs van Ginkel
 

Mark9473

Well-known member
Belgium
Is it reasonnable to expect the same brightness from both a 10*42 and a 8*32, all other parameters been equals

Making abstraction of the 10% brightness difference between a 4.2 mm and 4 mm exit pupil for dawn or dusk observations (i.e. your eye pupil being larger than 4.2 mm) you should keep in mind that the 10x42 view may not look brighter than that of the 8x32, but you will nevertheless have better detail recognition in the deep shadows in the 10x42. This is what's captured by the so-called twilight factor.
To what extent it matters to you, is hard to predict.
 

Maljunulo

Well-known member
Maljunulo, post 10,
This topic has been handled frequently on this forum, but I am happy to repeat it.
Brightness is determined by three factors; first of all the amount of light leaving the binoculars and that is determined by:
-1- the size of the exit pupil and
-2- the amount of light the optical system transmits.
Another factor is the color representation of the transmitted light since our eyes consider some colors brighter than others.
If I now look at the data we have obtained from the EL-SV 8x42 and the Victory SF 8x32 we see the following:
-a- the exit pupils are identical
-b- light transmission of the EL SV is over a broad range considerably higher then that of the Victory SF. Moreover the distribution of the transmitted light is for the EL-SV in favor of increased brightness observations.
My conclusion based purely on the measured data therefore is that the ELSV 8x32 shows greater brightness compared with the Victory SF 8x32.
I leave aside all personal properties of eyes, since that can differso much between different persons.
Gijs van Ginkel
Thank you.
 

Aotus

Well-known member
United States
Making abstraction of the 10% brightness difference between a 4.2 mm and 4 mm exit pupil for dawn or dusk observations (i.e. your eye pupil being larger than 4.2 mm) you should keep in mind that the 10x42 view may not look brighter than that of the 8x32, but you will nevertheless have better detail recognition in the deep shadows in the 10x42. This is what's captured by the so-called twilight factor.
To what extent it matters to you, is hard to predict.
... so... is this the part of that blog post that you're referring to? "The twilight factor alone does not permit any kind of real statement."

or, this part - "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." which basically says that with more magnification you can see more detail... I mean, that's useful to spell out, I suppose.
 

Gijs van Ginkel

Well-known member
Aotus, post 15,
A very simple experiment can illustrate your point.
Let us assume a very low light level and an object at a distance of let us say ten meters. I could not see any detail.
When I come now much closer to the object for example one meter I can see details of the object.
Something similar occurs using higher magnification.
Gijs van Ginkel
 

Maljunulo

Well-known member
When you move closer physically, doesn't the inverse square law apply, and when you increase magnification but remain at the same distance it does not apply?

I'm in over my head here, but I don't think the two situations are the same or equivalent.
 
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Rolosama

Member
Canada
These are the technical improvements of recent years in "-2- the amount of light that the optical system transmits." which now put the 10x42 ahead of the 8x42 among the birders.
 

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