Eye piece result

[poltabs]

I was wondering, what would give a better view (all things being equal) using a 12mm ep or a 24mm ep with 2x barlow? Thinking about sharpness, distortion and FOV? Would you see a difference between the 2 views?

Thanks

Kevin

[Brass n glass]

Almost certainly, especially if the eyepiece already has a Barlow in it (such as Vixen Lanthanum and Baader Hyperion) - Hugh

[Ajohn]

The barlow in the eyepiece is interesting. The shorter naigler zooms work like that and are very effective even on fast scopes.

Going back to the question. I didn't like barlows and then took 2 televue ones in part exchange on a scope I sold some time ago. Ones a big barlow and the other is a 5x powermate. These seem to work well. Looking at the cost though for a power of x2 it's probably cheaper to buy eyepieces. For very high power and imaging it may be worth spending the money on something like the higher mag powermates. Other wise I would be inclined to buy better quality eyepieces. It pays in the long run. 2 or more for the price of a 2ins 5x powermate.

John

[algol]

don't know whether my experiences speak for everyone mate but i only have the bog standard barlow that came with my scope, and i do notice a reduction in crispness when using the barlow over the unbarlowed (sp?) view

[Andrew*]

I was wondering, what would give a better view (all things being equal) using a 12mm ep or a 24mm ep with 2x barlow? Thinking about sharpness, distortion and FOV? Would you see a difference between the 2 views?

With a good barlow, it will effectively disappear and you won't see the difference.

Celestron Ultima/Orion Shorty Plus barlows are excellent, and Televue Powermates are outstanding. Meade Series 5000 telenegatives are also excellent.

Personally I find barlows a little frustrating (more tubes to slide around and knobs to tighten in the dark) and prefer to use eyepieces, but they can reduce the cost of your eyepiece collection considerably. I've just started using my barlows to increase my eyepiece collection. I can barlow my 14mm UWA to get a 7mm UWA and my 24mm Hyperion (when I get it) to a 12mm one. That one £50 barlow (GSO 2" 2x) saves me £150 on eyepieces!

Barlows also have the benefit of retaining eye relief that is often lacking in short focal length eyepieces.

[FLO]

... Would you see a difference between the 2 views?

Depends. A barlow can actually improve the performance of cheap eyepieces by reducing astigmatism at the edge of the field of view. It also allows the use of more comfortable longer focal length eyepieces with their greater eye-relief for high magnification viewing. The greater eye-relief is particularly useful for those who need to wear specs at the eyepiece. Otherwise it is generally better to use a single eyepiece. Also, simple eyepiece designs such as Plossls tend to barlow better than modern, more complex wide-field designs which essentially already have a barlow built-in.

HTH

[Ajohn]

There are cheap eyepieces about that have good eye relief - eg ebay ed's. They don't work well at high mags on f6 scopes though but are great at f9 and ok at f6 on lower mags. They come in focal lengths going up from 2.5mms

My own view looking at the economics is that working through usable exit pupil sizes and the things people are likely to want to look at barlows are a bit questionable. For planetary views a zoom is probably a cheaper option giving an exit pupil in the range of 0.6+ to 1.3mms on scopes up to about 200mms diameter. It takes a good scope to cope with the bottom of that range. (highest mag) eg 200/0.6+ x. Something like a vixen etc zoom does have decent eye relief. On top of that they are likely to want a lower power giving an exit pupil of around 5mms and something else to give about 2mms. The only drawback is the restricted field of view of the zoom at high mag but a barlow restricts that too. Later they might find they want some values in between but in my experience they don't relate to a 2x barlow. That's 3 eyepieces in total and if the zooms are suitable for the scope they have it will work out cheaper than a decent eyepiece and a decent barlow. Either way the zoom will fit into one useful range and if not for planets etc they might go for something that gives an exit pupil of about or just under 1mm for that. The bigger sizes of scope are going to need more eyepieces in the planetary range as they will be more sensitive to seeing conditions. A zoom lens really is a good bet in that case even on a 200mms scope.

Go the barlow root starting with a 5mms exit pupil and you will get 2.5mms with a 2x barlow. Ok but then comes planets so there is a need for another eyepiece at least. 3 chunks of glass how ever it's done and decent barlows aren't cheap. Most people would prefer the 5mms exit pupil eyepiece to be a 2ins. So forget that or buy a 2ins barlow and buy and eyepiece that gives a 2mms exit pupil and use that with a barlow for a 1mms exit pupil. Still 3 chunks of glass and so it goes on.

John

[Andrew*]

That's true - a zoom eyepiece is another way to save some cash...

[Ajohn]

I bought a zoom eyepiece about 25 years ago. It was Rubbish. Not so these days. Only problem is the cost of the short focus nagler zooms but if you think about the cost of the eyepieces they replace they aren't that bad. It's a pity vixen don't compete in that range.

The nagler zoom elements break down to a plossl and a barlow as do other eyepieces these days maybe even including ebay ed's. They do have the plus point that the barlow element will have been optimized to the plossl and in some case for shorter focus scopes too. Only problem in that direction is £. Hopefully as most scopes are in the shorter focal length range these days that might sort it's self out some day but at the moment getting the best out of something like even a F8 skywatcher 120mms refractor is likely to cost more in eyepieces than the optical tube costs.

John