Barlow questions

[murgen]

What is meant by the terms achromatic and apochromatic especially when referring to Barlows that are described as an improvement on ones that don't have either of those two designations?

I assume the SW 2x Barlow that came with my scope (200P) falls into this (lesser) bracket?

The TAL x2 is widely regarded on here, but the ads i have looked at just say they are the best available for the money and don't mention either of those words. Does this mean they don't apply?

Would it be worth buying a dearer Barlow to match the quality (if not necessarily the price-range) of the slightly more expensive eyepieces I will soon be buying, or is the TAL just about as good as it gets without spending silly money?

Does anyone know anything about the range of Barlows as sold on The Skys the Limit where the BST explorers ep's come from?

Cheers

M

[Tinker1947]

Me, I would forget the Barlow and buy EP's to suit the size the barlow would be used for,,,much better views with less glass in the viewing train...

[Peter Drew]

Barlow lenses that come with the "cheap and nasty" scopes usually have just one lens. Most decent Barlows such as the one supplied with your 200 SW will have two lenses and are achromatic, i.e. they will not introduce particularly noticeable false colour or distortion to the image. The more expensive apochromatic Barlows have two or three lenses some of which will be made of special glass to further improve the image. Your SW Barlow should be perfectly adequate for now, a better one would be the Tal. The most expensive ones might be worth considering in the future for imaging with short focus scopes.

[murgen]

Thanks for that view Tinker.

I've asked before if people with experience thought there were any advantages to unbarlowed eyepieces and not really had anyone's opinion.

I'm just setting up my new 200P/HEQ5Pro (boxes and bubblewrap everywhere).

The scope "manual" actually says there are benefits to be had by Barlowing - it mentions better eye relief and reduced spherical aberation.

I would have thought the fewer bits of glass the better.

As a new scope owner, i will most likely be buying a "set" of better quality lens in the near future, and of course a Barlow cuts down the number needed.

And thanks Peter (member 3158 here)

I'm surprised you say the SW basic 2x is achromatic, even the guy in the shop described it as worthless. I suppose he was seeing if he could get me to buy a bit more kit!

Of course, you're right - I'll have a good look through what I've got first.

[kenmyers]

The trick with barlows is they are brilliant - if you need them.

with a x2 barlow your 20mm eyepiece becomes a 10mm.

But

if you own a 10mm eyepiece, it will show much clearer image... much better than the 20mm with the barlow.

[Tribal-Wolf]

A 20mm with a barlow however may give longer eye relief than some 10mm EPs, which can help wearers of specs. Especially as the stock 10mm has poor eye relief. Just a thought lol

[kenmyers]

A 20mm with a barlow however may give longer eye relief than some 10mm EPs, which can help wearers of specs. Especially as the stock 10mm has poor eye relief. Just a thought lol

A good 10mm will have great eye relief and will always show a clearer image than a x2barlowed 20mm of similar quality.

[Tribal-Wolf]

A good 10mm will have great eye relief and will always show a clearer image than a x2barlowed 20mm of similar quality.

Of course which is why I mentioned some 10mm and mainly the stock 10mm.

[Tribal-Wolf]

One thing I often wonder with the 'extra' glass problem is how the more expensive an EP is, the more elements or glass it actually has. Obviously this will be better quality glass but it is glass all the same. I read a test once on zoom eps and one thing mentioned on a cheaper unit was because they had built the lower cost, less element ep so well that visually it was as good as the higher end ep, it was only let down by the body and zoom movement. Anyway just something to chew on.

[kenmyers]

agreed. I use ONLY and without exception "super low quality" eyepieces.

I have an F/8 scope and from some testing I have found a £200 6mm shows no better and no worse than a £15 6mm.

Same again with a £98 20mm plossl vs a £12 well used and abused 20mm.

Only noticeable difference was FOV is slightly slightly slightly more with expensive eyepieces.