Triplet vs doublet

[Sweety]

Hi guys is a triplet better than a doublet or is it down to the coatings of the binocular that make the difference. Thanks Darren.

[brantuk]

Scratch that - wrong section woops!

[Stu]

This seems to be in the correct section as it is about doublet or triplet binoculars. Sweetly please confirm this is correct

[Sweety]

Hi guys, yes its about binoculars, wondered if the triplets have better optics, been looking at the TS model20 x80 triplet.

[Dave In Vermont]

Not sure about binoculars, but triple-lenses in refractor telescopes cancel out chromatic aberration. CA is caused by the fact that the blue and the red spectra come to focus at different lengths. An achromatic lens, as the name indicates, attempts to compensate for this and bring them together at the same point - focal-length or FL. The slower the lenses, such as an F/15, the better the lenses are able to accomplish this, while an F/5 is likely to have some CA - especially when viewing bright objects such as the Moon. A triple lens system will show very little CA, if any at all.

In these days, most refractors are short ones with F/5 being common. And the cost of the triple lens ones can easily triple the price. Some folks are willing & able to finance these scopes. Others aren't all that bothered by the CA and keep their money. So it's a matter of personal taste. Not all that long go, most refractor sold to astronomy-people were the F/15 double-lens varieties. And these did take up a lot of space and were more difficult to transport. But the CA in them were much diminished.

I had a 3" F/15 when I first started out. Now I have an ST80 3.2" F/5. The CA in this doesn't bother me in the least. And there are filters which help to compensate available, though I hardly ever use them personally. They tend to give objects a yellow tinge.

Enjoy,

Dave

[brantuk]

It was my post which was in the wrong section - not the op. Mods please delete as necessary thanks.

[damnut]

+1 for Dave's comments, my grab & go is an st 120.

[Peter Drew]

A triplet isn't better than a doublet just because it's a triplet. Factors like glass types, quality control and setup all play a part, some triplets only just match first rate ED or flourite doublets. "Ordinary" Achro doublets, as mentioned, need to be long focus to compete with CA suppression. 

[Davey-T]

Triplets are generally heavier as well.

Dave

[BinocularSky]

Back to your specific question, the TS 20x80 triplet (sold in the UK as Helios Quantum 4), the colour correction is good on-axis and tolerable near the edge of field, but no better than a good achromat. Other things you should know:

* It's stopped down internally so it is effectively a 73mm.

* Konstantinos Makropoulos ("Pleiades" on here) measured the magnification as 19.1x - it is effectively a 19x73, not a 20x80.

* The low end of the IPD is 62mm; most have a minimum IPD in the high 50s - if you have a small face or close-set eyes, this binocular may not suit you.

I hope that helps.

[Sweety]

Thanks guys, I'll think I'll save and get an Orion resolux or Helios Apollo 15 x70. Thanks, darren.