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Thread: Using a Barlow lens with a diagonal

  1. #1
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    Default Using a Barlow lens with a diagonal



    Hi,

    Here's another newbie question so thanks for your patience!

    I just purchased an Orion Shorty 1.25" 2x Barlow lens. I also have a diagonal installed in the scope, and when I tried using it by inserting the barlow above the diagonal (before the eyepiece) the tube of the barlow seemed too long and it touched the mirror in the diagonal. I immediately removed it for fear of damaging the diagonal. It only seems to fit if I place it before the diagonal.

    Does it matter if the barlow is placed before the diagonal?

    Thanks!
    Equipment: Orion StarSeeker IV 150mm GoTo Mak-Cass Telescope, Celestron 8x42 binoculars, Canon Rebel T1i
    Lenses: Orion 32mm Sirius Plossl , Orion 12.5mm Sirius Plossl, (Svbony 23mm wide-field eyepiece, Svbony 10mm eyepiece - came with scope), Accessories: Orion Shorty 1.25" 2x Barlow, 1.25" Orion Variable Polarizing Filter

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    Default Re: Using a Barlow lens with a diagonal

    I thought I knew the answer - but to be sure I looked it up and saw an explanation that uses the Barlow in what I think it exactly the way you mention - which meant my particular explanation was wrong. Here's that link - look down near the bottom - I presume that is the position that fails for you?

    Why You May Need A Barlow Lens

    It may depend on where your scope focuses - but now I am not at all sure. It seems that you should be able to insert the Barlow where you would normally insert your EP. If you can't, something else may be going on.

    I imagine - without good knowledge - that perhaps the focus point is very close to where the diagonal is. If the Barlow lens itself isn't near the end of the tube (nearest the diagonal), maybe you have to have it inserted too far into the diagonal to catch the light cone at the proper point? The images I see on the web indicate that isn't the case though - so I am stumped.

    Will the diagonal itself move further into the tube?
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    Default Re: Using a Barlow lens with a diagonal

    What type of diagonal and barlow do you have rhliberman?
    A barlow can be placed in front of the diagonal with a refractor but it increases the magnification even more and may cause some abberations.
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    Default Re: Using a Barlow lens with a diagonal

    Quote Originally Posted by Gabby76 View Post
    What type of diagonal and barlow do you have rhliberman?
    A barlow can be placed in front of the diagonal with a refractor but it increases the magnification even more and may cause some abberations.
    The diagonal came with the scope (MakCass). The barlow is an Orion Shorty 1.25" 2x Barlow.
    Equipment: Orion StarSeeker IV 150mm GoTo Mak-Cass Telescope, Celestron 8x42 binoculars, Canon Rebel T1i
    Lenses: Orion 32mm Sirius Plossl , Orion 12.5mm Sirius Plossl, (Svbony 23mm wide-field eyepiece, Svbony 10mm eyepiece - came with scope), Accessories: Orion Shorty 1.25" 2x Barlow, 1.25" Orion Variable Polarizing Filter

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    Default Re: Using a Barlow lens with a diagonal

    If you can determine how far done into the diagonal barrel you can place the barlow you may be able to put an o-ring on the barlows barrel to hold it off the mirror.
    Are you using this for visual? With your 2 eyepieces listed only the 23mm would be useful with the barlow.
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    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
    Mounts: Celestron SLT w/ pier mod & EQ-3 tripod, Celestron hypertuned CG-5 w/ tracking motor & Argo Navis, Manfrotto 028B w/ Stellarvue M2C, Manfrotto 055PRO w/ 128RC, TAL-1 HD EQ, Vixen SXP w/ HAL-130 SXG & half pier
    Diagonals: 2" Astro-Physics MaxBright, 2" Zeiss/ Baader prism, 2" Baader Herschel Wedge (Photo Version), 2"
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    Default Re: Using a Barlow lens with a diagonal

    Quote Originally Posted by Gabby76 View Post
    If you can determine how far done into the diagonal barrel you can place the barlow you may be able to put an o-ring on the barlows barrel to hold it off the mirror.
    Are you using this for visual? With your 2 eyepieces listed only the 23mm would be useful with the barlow.
    Doh - I forgot to update my signature. I also have 2 Orion Plossl eyepieces - 32mm and 12.5mm.
    Equipment: Orion StarSeeker IV 150mm GoTo Mak-Cass Telescope, Celestron 8x42 binoculars, Canon Rebel T1i
    Lenses: Orion 32mm Sirius Plossl , Orion 12.5mm Sirius Plossl, (Svbony 23mm wide-field eyepiece, Svbony 10mm eyepiece - came with scope), Accessories: Orion Shorty 1.25" 2x Barlow, 1.25" Orion Variable Polarizing Filter

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    Default Re: Using a Barlow lens with a diagonal

    So really the only eyepiece that would need the barlow would be the 32mm? Your 23mm would be a 11.5mm and you have a 12.5mm already.
    With the focal length of your scope the 10mm would likely be unusable with the barlow.
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    Mounts: Celestron SLT w/ pier mod & EQ-3 tripod, Celestron hypertuned CG-5 w/ tracking motor & Argo Navis, Manfrotto 028B w/ Stellarvue M2C, Manfrotto 055PRO w/ 128RC, TAL-1 HD EQ, Vixen SXP w/ HAL-130 SXG & half pier
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    Default Re: Using a Barlow lens with a diagonal

    Quote Originally Posted by Gabby76 View Post
    So really the only eyepiece that would need the barlow would be the 32mm? Your 23mm would be a 11.5mm and you have a 12.5mm already.
    With the focal length of your scope the 10mm would likely be unusable with the barlow.
    At this point, yes, the 32mm is the only one. My 23mm eyepiece came with the scope and it's not that great.
    Equipment: Orion StarSeeker IV 150mm GoTo Mak-Cass Telescope, Celestron 8x42 binoculars, Canon Rebel T1i
    Lenses: Orion 32mm Sirius Plossl , Orion 12.5mm Sirius Plossl, (Svbony 23mm wide-field eyepiece, Svbony 10mm eyepiece - came with scope), Accessories: Orion Shorty 1.25" 2x Barlow, 1.25" Orion Variable Polarizing Filter

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    Default Re: Using a Barlow lens with a diagonal

    I would try using an o-ring as a spacer for your barlow and see if that keeps it from striking the mirror.
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    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
    Mounts: Celestron SLT w/ pier mod & EQ-3 tripod, Celestron hypertuned CG-5 w/ tracking motor & Argo Navis, Manfrotto 028B w/ Stellarvue M2C, Manfrotto 055PRO w/ 128RC, TAL-1 HD EQ, Vixen SXP w/ HAL-130 SXG & half pier
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    Ya gotta keep this Apo/
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    Default Re: Using a Barlow lens with a diagonal

    There should be a lip above the mirror to stop this from happening. I have one diagonal where this lip is really close to the mirror and gave the impression the mirror was being touched, when in fact it wasn't. Have a look to see if this is the case.
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