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Thread: Barlow: 2 element or 3 element?

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    I have a APO (3 element ) Parks & had tested it against a Meade 2 element barlow using the same eyepieces in the same scope with the same diagonal on the same objects, the Parks was better visually and so I sold off all my 2 element barlows. If you are using a regualr achro refractor doubtful you would see much difference but if you have a decent ED or triplet APO refractor scope of any quality yes you would see a definate difference since it maintains the 3 colors in focus. In a reflector telescope its pretty much unneccessary same goes for a regular achro as the focus is already off due to it being a flint/crown lens setup and already will have CA on bright objects before the barlow is introduced. So what scope are you using? Bottom line is it works best for APO refractors for visual. Testing it on my 8" dob I saw no difference that I could tell so its designed for hi-end refractors IMHO.

    Dave
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    I thought this observation should be stuck at the top of the EP forum. Thanks Dave.
    Last edited by WWPierre; 11-27-2010 at 05:45 PM.
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    Hi Dave,
    I suspect your Parks barlow is better quality than the Meade all-around. But much of the time, and with most good barlows I doubt you'll see much difference. When I started out using barlows (getting over my distaste of the cheap Tasco barlow I had in the 60's & 70's) I picked up a Klee and a 3-element Orion Shorty-Plus (same as the Parks & Celestron Ultima). Both performed much better than a Meade 126 I had borrowed to test. But once I tried them against a TV 2x (which is about the same price) I decided it has nothing to do with amount of elements, but has to do with how well the elements are made, and how good the coatings are. Anyway, I sold the Klee & Shorty Plus and only use a 2x & 3x TV's now.

    Oh yeah, I've tested these in my current 4" AT-102ED, my old XT-10, a CPC925, and an old Orion 90mm f/10 achro. Results were consistent between scopes.

    Hope that helps, or perhaps just confuses you more now. Hope not on the last part.

    Steve
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    I find 2x barlow to be enough.
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    Ive sold off my Parks & Mead barlows & am back to a TV Powermate again myself after many yrs. of experimenting with many barlows.
    Im really not all as critical as it would seem otherwise id own a super hi end triplet APO etc....
    I think its a personal choice when it comes to support equipment like barlows, one has to factor in their eyes condition etc...My eyes are not in great shape so I need all the help I can get to staff off blackouts & kidneybeaning etc...now if I was 20yrs. old with perfect 20/20 vision im sure a cheap run of the mill barlow would do me just fine.
    For the average Joe its not a major issue.
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    Default Re: Barlow: 2 element or 3 element?

    3 Elements barlows have more color correction than 2-element barlows. Each element has a different purpose whether it be color correction, coma correction or correction to get the desired magnification.
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    Default Re: Barlow: 2 element or 3 element?

    Just a note: most 2-element barlows have long focal lengths and, hence, long tubes.
    In order to shorten the barrels for SCTs and refractors, a shorter focal length is needed.
    This can be accomplished with deeper curves on the lenses, but that costs more money.
    If a third lens is added, the focal length can be shortened without requiring deeper concavities on the lenses.
    Yes, it can improve color correction, but the average two element barlow already has excellent color correction.
    The third lens is, primarily, added to shorten the focal length and shorten the overall barlow.

    Now, 4 element barlows are usually telecentric lenses (similar to a Bravais lens) and are very different beasts.
    But I thought you might want to know the truth behind the 3-element design.

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    Default Re: Barlow: 2 element or 3 element?

    i knew a guy that said that seeing was more important than what was in the focuser. i had to agree. after using alot of different barlows, including a klee. the tv 2x has been the best.

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    Default Re: Barlow: 2 element or 3 element?

    Quote Originally Posted by gene55 View Post
    i knew a guy that said that seeing was more important than what was in the focuser. i had to agree. after using alot of different barlows, including a klee. the tv 2x has been the best.
    Me, too.
    I guess I've been lucky enough to never having bought a bad barlow. When the seeing was good, all my barlows performed well.
    When the seeing was poor, they all performed poorly.

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    Default Re: Barlow: 2 element or 3 element?

    Thanks, Guys, for the comparisons of the different Barlows. It's a great help to a newbie like me trying to get to grips with getting a good one. I have seen time and again that I would be better off with a 2x rather than a 3X but I'm sure that if that's not so you'll let me know. I guess that over time I will be changing Barlows to see what is best for me and what I find to be the most "comfortable".

 

 
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