h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Binoculars - A1106560
Author: Gnomon - U151503

All you need to know about binoculars

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More emergence.

Yes I was thinking of doing the "Tits" Entry.

Oh, you saw my suggestion to Master B, did you?

No. But I expect his effort would be more mammarial than mine.

A1106560 - it's a good effort by the way. I don't have anything obvious to add.

Nothing much to add Gnomon, except that there is a test which *must* be performed before you buy a pair of binocs - after getting the focusing sorted, close your right eye and focus your left eye on a horizontal object in the distance, the top of a wall, say. Then open your right eye and close your left eye. If there is any slight deviation from the horizontal in either lens do not buy - the prisms (or something) are not aligned properly and it is a quick way to get a headache for yourself. Should not be a problem if you buy a reasonably well known brand. The point should be made though that as a result of this, you should never buy binoculars mail-order or over the internet unless you can be sure that if any problem is found, you can return them immediately.

Also, some binocs come with variable magnification (zoom) capabilities. They are quite useless for astronomy, as light capturing capabilities are sacrificed to do this.

Good work

Woodpigeon

This is a really useful entry Gnomon

A few suggestions:

"each with a lens at each end' How about 'both of which have a lens at each end'?

"and don't really need to know about' Well, I wouldn't mind learning a little about the prisms

"one eye is generally worse than the other" I wonder if there's a better way of saying that without using 'better' or 'worse'?

Is a monocular just another word for a telescope, and is it worth mentioning?


Scout

Woodpigeon, thanks for that tip, but I don't really understand it. How can I check if the image is horizontal?

Gosho, should I put in something about the prisms? I don't know how roof prism binoculars work exactly, but I took apart a set of Porro prism ones many years ago and understand the principles involved.

You don't have to include it but I think it would make the entry more complete. It doesn't need to be a detailed explanation full of refractory indexes and the like (if there even is such a thing as refractory indexes!), and I'm sure there must be plenty of websites which explain how they work


Scout

I was just wondering if there are special binoculars for people who wear glasses.

Also I believe that Zeiss and firms like that do make monoculars, which of course have the advantage of weight, bulk and price.

What configuration would you recommend for theatre/opera use? I suppose you'd need quite a wide field of view but not much magnification?

Ah - opera glasses. Yes, I think there should be a mention of those


Scout

Hi Gnomon,

Another nice entry.

In the "you may do with this information what you will" department...

For sailing/marine use 7 * 50 is recommended. Anything higher than 7 is difficult to hold steady. And you need the dim light quality of the 50 objective.

How about lens coatings? Has to do with minimizing the light reflected off the lenses. The colours you see are due to Newton interference. If the light's (energy) not reflected off the lenses, then according to Lenz' ( ha ha) law it must be going somewhere. So it goes through the lenses.

Is the prism / mirror arrangement to give you a longer effective focal length, without actually having to hold two long telescopes?

I have a pair of auto focus binoculars. I think the lenses are ground in such a way that you are looking through a different part depending on whether you are looking into infinity (almost //) or close up. (They fail your 20' criterium.) They are fine for looking at wild life from the breakfast table.

Awu.

Excellent entry!

Just a couple of comments -
Most modern 'nocs come with soft rubber eyecups which can be folded down to cut down on distracting light coming in from the side.
If you're going to be using the 'nocs in rough country where they might get knocked about, it's a good idea to look at the rubber-armoured ones.
For astronomical use, if you intend doing anything even semi-serious with them, a tripod mount or separate clamp is almost essential.
From experience, if your lens caps (and eye-caps if fitted) don't come with a cord attaching them to the body of the 'nocs, fit a cord yourself or wave good-bye to them at the most awkward possible time (Sods Law, para 4, sub-section ii[c]).

Wildman

Whew! That's a lot of comments.

>Woodpigeon's horizontal line test - I'm waiting on a further explanation of it from Woodpigeon
> each ... each - fixed
> prisms ... Yes, prisms are used so that you don't have to hold long telescopes in your hand. I'll put in a short description of them, although it may not mention refractive index.
> one eye worse than the other - Gosho, what's the objection?
> monocular - I don't know the difference between a monocular and a telescopy. Further research needed.
> marine binocs - info added thanks
> opera glasses - section added
> binocs for glasses wearers - section added
> lens coating - that was already there
> rubber eyecaps and rubber padding - I'll add something
> lens caps on string - I'll add something
> tripod for astro work - no. I don't agree. The best way to look at the sky using binoculars is lying on your back with your head firmly on the ground.

Ausnahmsweise - are they really auto focus? How do they work? Is there electronics involved?

Yeah! OK, I'll agree with you on 'lying on your back with your head firmly on the ground' for astronomical work - I must admit I never thought of that (it's usually too wet in Scotland). I thought I was lazy using a chair and tripod.
As for the monocular/telescope thing, I've always thought understood that if the lenses were in a straight line it was a telescope, if they were off-set then it was a monocular - but that's really only an opinion (probably wrong now I think about it - some of the bird-watching and sighting telescopes I've used have been off-set with prisms).
I don't know if it would be worth mentioning some of the more modern variants, night vision sets with light-amplification electronics or the ones with built in cameras - might fit in with the auto-focus ones mentioned.

The amount of comments you're getting just show what a good choice of subject you found, your entry is very well written and interesting, so it's bound to attract comments - even from committed lurkers like me.

Wildman

Gnomon - re the horizontal view, I should have explained better : its just a matter of closing your right eye and keeping your left eye open, then closing your left eye and opening your right eye - do it a few times in rapid sequence while keeping the the wall in the distance in focus. If you see any difference - ie if the top of the wall in one eyepiece seems to be marginally higher than top of the wall in the other eyepiece, there may be an alignment problem.

Thanks. I'll think about that and try it out this evening.