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Thread: Barlow Lens x3 or 4mm Lens

  1. #1
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    Default Barlow Lens x3 or 4mm Lens



    Hi there all

    Well I'm still very new at astronomy. Been having allot of fun with it the past year getting more lenses filters etc. Planning to start AP soon. But for now here's my problem. I own two telescopes. The one I need advice with is my Celestron 130 slt. 650mm Focal legth and 130mm appature. The eye pieces I have are 25mm, 20mm, 15mm, 10mm, 9mm and 6mm. I also have a Barlow x2.

    So as you can see my maximum magnification is about x216. My telescopes maximum is on x306. Now I don't make too much money so I buy everything piece by piece Id like to get the most from my next purchase which will either be a 4mm lense or a Barlow x3. I wanted to get some advice from you guys. The 4mm and Barlow will get me the same magnification just just over the maximum on x325.

    Now also taking into consideration I want to buy a cctv camera for my telescope.(Not sure if they get used with a Barlow I still need allot of research into AP before I start) If this is irrelevant. The only factors I am concerned about are, Quality of image and then if quality is not a factor the Barlow will win due to the bigger eye piece that would give better eye relief.

    Thanks in advance

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    Default Re: Barlow Lens x3 or 4mm Lens

    Welcome to the foruim.

    YOur scope has a focal ratio of f/5 (=650/130). Its maximum maxnification in normal conditios is 130x (equal to your aperture in mm). Its maximum magnification in rare, excellent conditions is 260x (= 2 * the aperture). These magnifications would be achieved with 5mm and 2.5mm eyepieces, respectively.

    Forget the 306 figure; that is marketing hype. Atmospheric conditions will never be good enough for that. The figure you should aim for is 130x. For planetary viewing, I would recommend a 5mm eyepiece. Have a 2x barlow on hand for those rare occasions when you can push it to 260x. (I wouldn't run out and buy a 5mm eyepiece. The 6mm you have will be pretty close.)

    Having said that, high magnification is only suitable for a few targets. Planets, mostly. If you wish to look at DSOs, you are better of with low magnification.
    Last edited by KathyNS; 05-10-2014 at 11:14 AM.
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    Default Re: Barlow Lens x3 or 4mm Lens

    Most manufacturers Rate their scopes to be able to "achieve" 60x per inch of aperture of HIGHEST USEFUL magnification......BUT that is in THEORY and it also would have to have absolutely perfect conditions... Maybe on the surface of the moon with NO ATMOSPHERE your scope could deliver the rated amount but from here on the surface of the Earth we are looking thru several miles of JUNK in the atmosphere

    SO BELIEVE KEITH you will never ever be able to get that amount of magnification out of your scope with the possible exception of the moon since it is so big and so bright as well as being so close...

    I own a bunch of scopes...and I use them ... I bet I do not go above 250x with any of them but maybe 3 times a year total ...and only go above 200x about a dozen times (at most) a year...

    Astronomy is NOT about magnification it is all about gathering as much light as possible... Microscopes are about magnification NOT Telescopes

    If you have to BUY SOMETHING consider a dedicated Observation Chair...which are well worth their money in Gold...and not for you back legs or tail end ..the chair is for your eyes..you simply see better and for longer periods of time using a chair......

    Clear skies

    Bob G
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    Default Re: Barlow Lens x3 or 4mm Lens

    When I 2x Barlow my 8mm eyepiece with my f/5 scope I get 188x magnification. That seems to be the sweet spot with planets with my scope on most nights. I would bet if you 2x barlow your 9mm to get 144x magnification, that will be close to your sweet spot with your f/5 scope for planets on most nights.
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    Default Re: Barlow Lens x3 or 4mm Lens

    Thanks allot for all the replies as mentioned I still quite fairly new to all this. I must admit I am very fortunate to live where i do. Nice and high on a mountain resort. Only light pollution I get is the moon! Ill save my money then for the Photography I'm planning to start with. So ill go post there and start getting advice for that

    Thanks again everyone!
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