Binoculars convention should be Aperture Divide Magnification, not Magnification x Aperture... ? (1 Viewer)

[kimmik]

Mathematically it makes no sense. What is the point of Magnification multiply by Aperture? There is no parameter as far as I can tell, that is calculated with this multiplication.

Whereas, mathematically, Aperture divide by Magnification will correctly calculate the exit pupil, and give you the same critical information in a succinct fashion.

50/12 binocular - 50mm aperture/12 magnification = 4mm pupil
32/10 binocular - 32mm aperture/10 magnification = 3.2mm pupil

The reason I see the 12x50 and 10x32 being convention:

1. division scares people.
2. new comers care more about big magnification than big exit pupil.
3. people prefer to operate on linguistics rather than mathematics. "12 time magnification 50mm aperture" is linguistically easier than "50mm aperture divide 12 times magnification".

 

[StephenHampshire]

Mathematically it makes no sense. What is the point of Magnification multiply by Aperture? There is no parameter as far as I can tell, that is calculated with this multiplication.

Whereas, mathematically, Aperture divide by Magnification will correctly calculate the exit pupil, and give you the same critical information in a succinct fashion.

50/12 binocular - 50mm aperture/12 magnification = 4mm pupil
32/10 binocular - 32mm aperture/10 magnification = 3.2mm pupil

The reason I see the 12x50 and 10x32 being convention:

1. division scares people.
2. new comers care more about big magnification than big exit pupil.
3. people prefer to operate on linguistics rather than mathematics. "12 time magnification 50mm aperture" is linguistically easier than "50mm aperture divide 12 times magnification".

No 3 -"8 times" magnification, written as 8x - It is a convention it doesn't have to make sense.
For most people using in decent light the objective size is not important, except as a rough idea of the likely size of the bino. Neither 42/8 or 8x42 tell you a lot about important things like "can I use it with glasses?" "will the eyecups fit my face?" "how sharp is it" etc

 

[Mono]

8x30 is not a sum. It indicates 8x magnification with a 30mm objective. It is a convention, that is all.

 

[GrampaTom]

Kimmik, Wasn't at all sure what you were asking...
Interesting that I went there. It took Stephen's #2 before I got it. I'd never thought of 8x42 as a formula. 8x42 is a labeling system, indeed to quote Stephen "it doesn't have to make sense". At least till now... Ha! Thinking of lumber, 2x4 - that 2" (actually 1.5 or metric equivalent) by (rather than times) 4." 8x42 is similarly sorta like 8 by 42. My sense is that folks who know binos, know this and folks new to them need to have the numbers explained anyway. Once explained, whats needed? What do you think might be accomplished by changing this convention?

 

[Binastro]

Not only does magnification and aperture make sense, and it doesn't have to be a x sign. It could be a dot for identification on the binocular.

But for astronomy magnification times aperture is a very accurate measure of the faintest stars that are seen and also for general astro performance.

Other more complex ideas have been put forward, but for me and other experienced astronomers magnification times aperture is an accurate practical formula for comparison purposes.

Within reason, I am not talking about 50x50 binoculars, but general normal magnifications and apertures from say 8x20 to 20x80.

A friend's 20x50 showed much fainter stars than a 10x50, despite the probable derision from members here.
This was hand held but at a fairly high elevation to the horizontal.

I don't think that division deters people.
Any math deters many people.

Regards,
B.

 

[Maljunulo]

8x30 is not a sum. It indicates 8x magnification with a 30mm objective. It is a convention, that is all.

This.

It is not a mathematical expression.

 

[Binocollector]

A friend's 20x50 showed much fainter stars than a 10x50, despite the probable derision from members here.

Why derision? The 18x50 Canon or 20x60 Tento are both great for stargazing. What's wrong with 20x50?

 

[Maljunulo]

A friend's 20x50 showed much fainter stars than a 10x50, despite the probable derision from members here.
This was hand held but at a fairly high elevation to the horizontal.

The higher magnification makes the background darker, thus enhanced contrast enables us to see the fainter ones.

My 16X70 always showed fainter stars than my 10X70. (both Fujinon FMT-SX)

 

[Maljunulo]

Post #1

What you are proposing would result in identifying binoculars by their exit pupil size.

Therefor a 7x50 and a 10x70 end up with the same descriptor.

This is sheer madness, and would create total chaos.

What did I not understand?

 

[GrampaTom]

Maybe it was a slow day... a joke?

 

[John M Robinson]

I always read 7x35 or 8x42 as 7 by 35 and 8 by 42. Even as I wrote it, I was saying by in my head.

 

[John A Roberts]

As a convention, the long standing practice of describing binoculars in terms of Magnification 'x' Objective Diameter does have some explanatory value.
It both describes the (nominal) magnification of a particular binocular, and gives some idea of relative physical size.

In the back row: x25, x30, x32, x42, x50, x56.

Cropped and adjusted from Gordon (aka proudpapa56) at: Honey Creek Bill and Beak | eBay Stores


And if one’s interested, it’s relatively easy to calculate the exit pupil size - at least in terms of diameter.


However, when considering the size of an EP, what’s really informative is the area - rather than diameter -
as a relatively small increase in diameter can result in relatively large increase in area.

Increase in Diameter vs Area:
1.2x dia . . . 1.5x area
1.4x . . . . . . 2x
1.7x . . . . . . 3x
2 x . . . . . . . 4x


The formula for the area of a circle is π r2.
However for convenience, to calculate the relative area of a circle, we can:
eliminate the constant π, and; then square the diameter, without first dividing it to obtain the radius.

So some comparative examples of EP’s (diameter in mm > relative area):
8x16 (2 > 4) . . . . . 8x20 (2.5 > 6.2)
8x24 (3 > 9) . . . . . 8x28 (3.5 > 12.2)
8x32 (4 > 16) . . . . 8x30 (3.75 > 14)
8x40 (5 > 25) . . . . 8x42 (5.25 > 27.6)
8x48 (6 > 36) . . . . 8x50 (6.25 > 39)
8x56 (7 > 49) . . . . 8x60 (7.5 > 56.2)

- - - -
And while with binoculars the objective lens diameter generally corresponds to the effective aperture (and therefore consequent exit pupil),
there are exceptions.

Firstly, in the Allbino’s tests the observed EP’s are often less than perfectly circular, so with somewhat less then the nominal area.
And much more significantly there's the example the Optolyth Alpin 12x50, with an EP of 3.5 mm verses the expected 4.2 mm
- so with a 30% reduction in area, resulting in what's effectively a 42 mm objective!
See post #3 at: Pentax 8x32 DCF ED review by Roger Vine


John

 

[CharleyBird]

As a child in junior school we were taught feet and inches. I remember asking my parents what 8x30, 17x50 and 20x50(a telescope) meant, and having the metric system first explained, then the labelling system.

 

[kimmik]

Thinking of lumber, 2x4 - that 2" (actually 1.5 or metric equivalent) by (rather than times) 4.

In this case, the multiplication is the correct descriptor of cross sectional area of the lumber.

It could be a dot for identification on the binocular.

A dot is the shorthand symbol for multiplication, so in a way that is the same as x.

But for astronomy magnification times aperture is a very accurate measure of the faintest stars that are seen and also for general astro performance.

This is my favourite explanation so far, where the mathematical product of MAG x APERTURE has a real world correlation.

 

[Binastro]

It should say: 8x, 32mm or 8x linear magnification, 32mm objective clear diameter.

With early binoculars it just said 6x or 8x or with Galilean field glasses nothing at all.

The most important factor with a binocular is the linear magnification.
Some bright sparks used to say area magnification to increase sales to the public.

The next important thing is the diameter of the front glass, which indicates the brightness of the image in many situations.

The third and less important factor is the size of the FOV.
For some reason in the U.S. it is given as feet at so many yards. Strange to me, but fully understandable in the U.S.

There should be with Trading Standards, who deal with weights and measures, a set description, naming the A x B on binoculars as the linear magnification and the diameter of the objectives.

False descriptions such as 200x25 should result in the seizure and destruction of the whole stocks in warehouses and sellers, with fines for the owners of said outlets.
This is wasteful, as the 200x25 might well be quite useful 10x25s, but might reduce the scams to which the public are subjected daily.

Theoretically, Trading Standards in the U.S., the U.K., Europe and Japan could enforce these rules, but they are understaffed, underfunded and there are more important issues, such as fake medicines etc.

Binoculars are way down the list.

Regards,
B.

 

[Mono]

In this case, the multiplication is the correct descriptor of cross sectional area of the lumber.

Unless it is 4"x 2" PAR then they are the measurements before the wood is planed! The actual timber is about 1/4 smaller in each dimension!

 

[kimmik]

Another theoretical way to specify is MAG x PUPIL.

I had a chance to try the leitz "6x24", next to uv "8x32" and uv "10x42". These three to the eye feel very similar due to the same exit pupil, with the visual difference being magnification, and physical difference being binocular size.

So 6x4mm, 8x4mm and 10x4.2mm is another means of specifying these binoculars, to be both mathematically and linguistically consistent.

But.....

Any math deters many people.

 

[kimmik]

It should say: 8x, 32mm or 8x linear magnification, 32mm objective clear diameter.

This may be the best option, to remove the ambiguity by adding the unit and a comma.

Its weird that american specifications use metric for aperture, but foot yard for FOV. Just yet another inconsistency I guess.

 

[Mono]

If you search for old binocular adverts you will see the magnification x objective (in mm) description used from 1900ish even in the USA. I can find some 1880s British adverts than use inches for the objective but that is mentioned in the body text not as 8x2½. It seems to be common in early adverts not to mention the objective at all just state the available magnifications. I have found one use of the comma, 8x, 30.

 

[Owlbarred]

"If it ain't broke, don't fix it."