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    Question Help with Barlow lens 2x



    Hi everyone, i need your help with a problem that i noticed when i was using my Barlow lens 2x.
    I bought omegon 2x achromatic lens on amazon (i can't post links) and i used it with a Celestron 114 LCM (all the specifications are on the official site) and the 9mm eyepiece included in the box. When i used it the first time i noticed that it increased the magnification properly without going out of the limit, but i couldn't completely focus it.
    That evening the sky was a little cloudy, but removing the lens i could see a lot better.
    I read that maybe the focuser couldn't reach the focal point, but i'm not completely sure and i wanted to ask your opinion.
    I hope you can understand what i mean, i'm not english :P.
    Thank you for the help!

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    Default Re: Help with Barlow lens 2x

    It is possible that this combination of eyepiece and Barlow in your scope will not allow you to reach focus, but it is more likely that using a 2x Barlow with the 9mm EP was simply too much magnification for this scope.

    The Barlow effectively makes the 9mm EP a 4.5mm. Your scope is an f/8.77 (ratio of focal length to aperture: 1000/114 = 8.77). A general guideline is that an eyepiece with a focal length less than the f ratio of the scope will give an image that is too dim and blurry to be useful. Barlowing the 9mm to a 4.5 will only give good results on rare nights of exceptional seeing (atmospheric conditions are optimal).

    With 4.5mm EP, th magnification of your scope is about 222x. That is a lot for this scope; a more realistic maximum useful magnification is probably around 90x - 120x at best. So it is possible that the scope was in focus, but the image at 222x was so dim and fuzzy that it appeared to be unfocused.
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    Default Re: Help with Barlow lens 2x

    in what direction can't you reach focus ,in or out ?
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    Default Re: Help with Barlow lens 2x

    Your scope should be able to do 200x easily with a straight out eyepeice. Using a barlow just puts another lens inline with the EP giving it less visual clarification. I never use them because of this. I've also experienced out of focus views with barlows. That's why I strictly use eyepeices. With your setup I would think the lowest I'd go is a 6 mm piece. You have to remember that the lower you go, the dimmer the view is gonna be, and with a 114 mm scope it's gonna be pretty dim. I usually don't go lower than a 5mm on my 8 inch scopes and my 11 inch scope. It's even dim views on them.

    I have a 102mm refractor and I only use down to a 10mm. It's all about the view, not the magnification.
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    Default Re: Help with Barlow lens 2x

    Quote Originally Posted by yobbo89 View Post
    in what direction can't you reach focus ,in or out ?
    Hi yobbo, i'm going to try and tell you this evening.

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    Default Re: Help with Barlow lens 2x

    As stated above you're probably using too much magnification for your scope. Although, it depends on the specific target in some cases. If you're looking at a large bright object such as the Moon, high magnifications may be possible, depending on atmospheric conditions.

    There are a lot of myths about Barlows, most of them are false.
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    Default Re: Help with Barlow lens 2x

    Hi and thank you all for the answers.
    So the problems can be two:
    1)Too high magnification (and too bad seeing).
    2)The barlow itself.
    Is it better with a 5mm/6mm EP without barlow? Which of the two should i buy?

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    Default Re: Help with Barlow lens 2x

    Quote Originally Posted by BiSam View Post
    Hi and thank you all for the answers.
    So the problems can be two:
    1)Too high magnification (and too bad seeing).
    2)The barlow itself.
    Is it better with a 5mm/6mm EP without barlow? Which of the two should i buy?
    1) You haven't said what you were specifically observing. Many faint deep sky objects will be increasingly difficult to perceive at high magnifications. Seeing and transparency are also huge factors on the ability to use high magnifications.

    2) Is this the Barlow? https://www.omegon.eu/barlow-lenses/...c-1-25-/p,2289



    It may be the same as my 'Meade' 2x Barlow.

    There's a lot of misinformation about Barlow lenses. They do not necessarily have to be expensive to be effective, but they do have to match what you are using it with and what you are observing. The biggest fallacy is that Barlows add unnecessary additional glass into the light train. Many eyepieces have Barlow or Smyth lenses as part of their design and construction anyway. A decent Barlow that is well matched to the telescope and eyepiece it is being used with shouldn't even be noticeable in use.

    In my experience this is only discovered through trial and error.

    If your scope has a 1000mm focal length a 6mm EP will give you about 167x. This might be good for the Moon, possibly even Saturn and Jupiter in good conditions with your scope.
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    Default Re: Help with Barlow lens 2x

    Question for Shorty Barlow: the OP's scope has a focal length of 1000mm but the OTA is less than half of that, indicating that this is a Bird-Jones type scope. How well do Barlow lenses work with these scopes, given that they already have a Barlow-like corrector lens in the focuser?

    Comment for BiSam: a 5mm EP will give 200x in your scope, and I stand by my comment that that would give you disappointing results about 99% of the time. I agree with Shorty Barlow that a 6mm EP could work for you when the seeing is good, and there would be no harm in trying an inexpensive 6mm Plossl in your scope. Even if you only use it on the rare night with great seeing, it will be a good addition to your equipment. Who knows what other scope(s) you might get later? I bought a 7mm EP years ago, before I knew much about telescopes, and it was unusable in my f/10 Meade SCT. I held onto it for about 15 years, and now use it all the time in my f/6 refractor.
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    Default Re: Help with Barlow lens 2x

    Quote Originally Posted by Shorty Barlow View Post
    1) You haven't said what you were specifically observing. Many faint deep sky objects will be increasingly difficult to perceive at high magnifications. Seeing and transparency are also huge factors on the ability to use high magnifications.

    2) Is this the Barlow? (link)

    (image)

    It may be the same as my 'Meade' 2x Barlow.

    There's a lot of misinformation about Barlow lenses. They do not necessarily have to be expensive to be effective, but they do have to match what you are using it with and what you are observing. The biggest fallacy is that Barlows add unnecessary additional glass into the light train. Many eyepieces have Barlow or Smyth lenses as part of their design and construction anyway. A decent Barlow that is well matched to the telescope and eyepiece it is being used with shouldn't even be noticeable in use.

    In my experience this is only discovered through trial and error.

    If your scope has a 1000mm focal length a 6mm EP will give you about 167x. This might be good for the Moon, possibly even Saturn and Jupiter in good conditions with your scope.
    Yes, it is the barlow i used with moon and mars.
    Will 6mm be right even for less visible objects like comets and deep space objects?
    Thank you!

 

 
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