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  #1  
Old 03-02-2018, 09:48 AM
Mick1 (Mick)
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Barlow's

What's the difference between a short and long barlow, and is there a preferred type for different telescopes, for example a short barlow maybe better suited for a Reflector telescope. I'm in the market for one and this has got me wondering which one is best suited for my refractor.
Also is it best to put the Barlow between the focuser and diagonal or between the diagonal and eyepiece.

I'm thinking if I put a barlow between the diagonal and the eyepiece I can screw a polarized filter on the barlow and another one on the eyepiece, that way I can leave everything in situe and just turn the eyepiece to get the variable polarizing effect. (I do have 2 polarizing filters)
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  #2  
Old 04-02-2018, 08:12 PM
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doppler (Rick)
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A long barlow will fit in most newtonians but the barrel is too long to fit in a diagonal or in my case the focusser of my mak cassegrain even without the diagonal. If you put it in before the diagonal the eyepiece might not come to focus. Barlows are designed to have an eyepiece (or camera) fitted directly to the top.
ps my diagonal is threaded so the 2 filter idea would work, just tried it on my diagonal and it works fine, a moon test would be great but it's raining tonight.
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  #3  
Old 04-02-2018, 08:29 PM
bigjoe (Joe)
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Quote:
Originally Posted by doppler View Post
A long barlow will fit in most newtonians but the barrel is too long to fit in a diagonal or in my case the focusser of my mak cassegrain even without the diagonal. If you put it in before the diagonal the eyepiece might not come to focus. Barlows are designed to have an eyepiece (or camera) fitted directly to the top.
ps my diagonal is threaded so the 2 filter idea would work on my diagonal

Some of these Barlow types have tradeoffs.

Shorties...their compact and easier to manage, but may cause vignetting in longer focal length say 32mm eyepieces , and even add some astigmatism in the periphery and other problems with such a rapidly changed lightpath...a reason I gave up on the cheapy shorties years ago.
The longer ones ..not so many problems.

A good TV barlow for example was designed to be used with their EPs , and mixing brands can lead to undesirable outcomes...thats my experience.

bigjoe.
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  #4  
Old 04-02-2018, 10:36 PM
ausastronomer (John Bambury)
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Quote:
Originally Posted by bigjoe View Post
Some of these Barlow types have tradeoffs.

Shorties...their compact and easier to manage, but may cause vignetting in longer focal length say 32mm eyepieces , and even add some astigmatism in the periphery and other problems with such a rapidly changed lightpath...a reason I gave up on the cheapy shorties years ago.
The longer ones ..not so many problems.

bigjoe.

Hi Rick,

Joe is pretty close to correct. The Orion Shorty Plus (also sold as the Celestron Ultima) was one exception. This was a high quality Japanese made 3 element Short Barlow which worked very well. It had 23mm clear aperture which compares to some other short barlows like the University Optics Klee which only has about 18mm clear aperture and vignettes quite badly with longer focal length eyepieces. The Orion Shorty Plus isn't the same as the Orion Shorty Barlow which is Chinese made POC.

The Orion Shorty Plus is quite good but the longer Barlows like Televue, Dakin, Baader/Zeiss and Astrophysics are slightly better, with the Dakin and Zeiss being the best IMO and just in front of the other two. That having been said, you need good seeing conditions, a high quality telescope and a skilled observer to pick them apart. I owned an Orion Shorty Plus for many years in company with a 1.8x TV Barlow, a 2x TV Barlow and a 2.5x TV Powermate. It compared quite well if just a fraction behind the others.

These are still around 2nd hand and work well in a refractor. I wouldn't recommend any other short Barlow.

Cheers
John B
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  #5  
Old 05-02-2018, 06:49 PM
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As John said , the Shorty is a great Barlow , I have the orange lettering Celestron Ultima 2x and it is awesome with my TV Plossl's as it just disappares in use eg. I don't even know its there , very good indeed working excellently in all my scopes , f6 through to f11 reflectors , SCT's and refractrors ..

Brian.
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