Why 42mm? (1 Viewer)

You’ve said this yourself, and I agree, that the shortest path to 8x42’s becoming standard would be via 7x42’s being widespread—since 7-power used to be much more of a norm, and 7-power X an even 6 mm exit pupil = 42 mm aperture—and companies vying to give consumers ‘more power’ (8x magnification) at that same size and weight.

So there’s certainly nothing preordained or ‘natural,’ much less optimal, about it. I—like Chandler Robbins!—much prefer 10x50, given the choice.

Steve, post 20,
An ice-cold shiver arises round my heart, but fortunately I have a view on some 42 mm binoculars: the Hensoldt Jagd Dialyt 6x42 and 7x42 made between 1936 and 1943 and an even older one the Jagd Dialyt 6x42 around 1920 and certainly not to forget the Zeiss 6x42 from 1914-1919. That must prove my innocence.
Gijs van Ginkel

dries1 said:

If one thinks about it, the 8X42 and 10X42 format is the most versatile, lighter than the 50s and easier for eye placement and cover a wider range of viewing conditions (low light) than 30-32. Why they changed from 40 to 42, I have no idea.

Andy W.

Click to expand...

10x40 (dialyt) was a 'standard' for a long time. A x40 binocular has 12.566 cm^2 of objective glass surface.
a x42 has 13.854cm^2 surface.

That difference is 10%... So suppose you could build a binocular x42 that is 10% dimmer than your x40 competitor because of inferior glass (or better: you try to market your binocular with the same glass but 10% more surface as 10% brighter), you have a winner. The weight difference between x40 and x42 will not be 10%. So it's all in the marginal gains: you can have a significantly brighter binocular with a very minor weight penalty. You cannot go to x50 or you would get a significant weight penalty.

So I guess some companies (Leica) tried to conquer market going to x42, but as the alpha brands all went x42, it would be a bit silly to go x43 or x44 because the coatings and transparency improved so there was no need to go bigger in order to reach an improved view.

I think that the use of 42mm is purely the attractiveness of 42 compared to 40, as a number and for a sales pitch.

Gentlemen only bought things in guineas, and gentleman's shops only sold in guineas.
A guinea is 21 shillings or £1.1s.0d.

Two guineas is 42 shillings.

A typical drawtube telescope in the early 1950s cost £12.12s.0d.
As did a basic reflecting telescope.

A man's suit was priced in guineas and often tailor made.

It was unusual to see something in straight pounds.

Today guineas are still used for auction prices and professional fees.
There are still horse races designated in guineas.

Nowadays, £9.99 is the selling point. A bargain compared to £10.

As to the weight of a 42mm binocular compared to a 40mm. It is likely to be somewhere between the square and cube of the objective size. I cannot see weight being a reason for the change from 40mm to 42mm.

The reason why 41mm and 39mm binoculars aren't common, if at all used, is simply that these numbers are not attractive. There is absolutely no actual reason that 39mm and 41mm binoculars shouldn't be made. But they won't sell.
The fact is that many binoculars are vignetted and the real objective size is less than that marked, so 42mm might well actually be the dreaded 39mm.

I note that there were Carl Zeiss 8x39 binoculars made about 1916.
And Soviet binoculars the same made on Zeiss machinery.

I also see 8x41.48 modern binoculars on Amazon.

What a strange world.

But in the main we don't buy things according to logic, rather we buy for emotional reasons.

How 'New' can washing up liquid be that is basically the same for the last fifty years. Yet the bottle says New.

The Zeiss Harpia says 95mm, but it is nearer 93mm.
I think the Leica Apovid 77 might be about 75.5mm, although I haven't measured it. I think it takes 77mm filters.

Binastro, your theory is by far the best! I love it. Guineas and attractive numbers it is.