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Thread: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

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    Default Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3



    Hello all,

    this is the 2nd test of these both eyepieces on the globular clusters.
    These eyepieces, and some more, have been acquired during the long bad weather season since 2017.

    The M53 in Coma Brenices is a condensed looking globular cluster, requiring high magnifications, and the optics delivering pin point stars. Hence, I have been pretty curious what the 6” F/5 Synta achromatic refractor will resolve, and what will be left not resolved.

    The Pentax XW 3.5mm eyepiece has shown at the magnification of 214x an incredibly bright ‘cotton ball’ with about a dozen of pin point stars “jumping out and back”, besides some stars which have been seen steadily, of course.

    The Baader Classic Ortho f=6mm has been barlowed with the 2.25x factor from the Baader Q-set, increasing the magnification up to 278.8x (f=2.69mm equivalent, 0.54 exit pupil). This magnification is well above the 250x, generally recommended for the 6” F/5 fast achros.

    The resulting crappy 11.2 arcminutes TrueFOV have asked for quite a bit of patience to ‘press’ the M53 globular cluster into the field of view.
    However, the view has been really rewarding with more than 2 dozens of stars resolved as fairly well defined pin points, leaving some unresolved fine granulation across the cluster core.

    The M3 in Canes Venatici belongs to my favourite globular clusters during the May season.
    Both the Pentax XW 3.5mm and the barlowed BCO 6mm have revealed comparably nice resolved views with the pin point stars.

    The barlowed BCO 6mm looks like a nicely performing budget alternative to the Pentax XW 3.5mm for the maximum magnifications on the fast F/5 refractors.
    Also of interest is the size comparison

    BCO Pentax XW comparison.jpg

    Technically, I prefer to mount the Baader Barlow triplet lens in the Baader helical focuser, instead of the Baader Barlow tube,

    Barlow and helical focuser for the BCO.jpg

    Date and time: 8th May, 2018, 23:00 – 00:15 local summer time
    Place and observing conditions: Backyard, NELM 5mag
    Telescope: 6” F/5 Synta achromatic refractor
    Eyepieces: Pentax XW f=3.5mm (214x), BCO 6mm barlowed 2.25x f=2.69mm (278.8x)
    star hopping eyepiece Antares W70 f=25mm (30x)

    Thanks for reading, and clear skies,

    JG
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Good stuff JG. Thank you for the review of your observing results here. I appreciate very much.:-)
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    Mark

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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Thanks for the comparison, with good budgetary news for 6mm BCO- owners!

    But more than thanks for you technical solution for mounting the Baader barlow in the Baader helical focusser!! Never have thought of that!

    I knew I could mount this Barlow in my Baader T2 prism, or in the Baader mirror-diagonal. It shortens the optical path if I want to use my ADC for planets by centimeters. (at a lower barlow-factor of course)

    But this is new and never ever occurred to me!
    THANKS!!!

    John
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Nice evaluative views, JG. You really cranked up the power on these globs to good results. Very nice, sir!
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Quote Originally Posted by bladekeeper View Post
    Nice evaluative views, JG. You really cranked up the power on these globs to good results. Very nice, sir!
    Hello Bryan,

    I would have never believed, that I can go on a fast achro as short as with 2.69mm

    One more good news: The Q-barlowed BCO 6mm is nearly parfocal with the cheap Antares W70 25mm - my star hopping EP.
    This helps quite a lot as finding the focus on the barlowed BCO may turn out to be tricky.

    Hello John,

    I insert sometimes the Baader helical focuser, leaving the GSO focuser just for the rough focusing approach.

    Clear skies,

    JG
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Thanks for the shootout JG! I am a big fun of BCOs to as you know. Except as you highlighted small FOV and short eye relief make using orthos with manual mounts somewhat challenging. Baader Q-turret is a nice solution to the problem: target with 32mm Plossl and flip to 6mm BCO. All set with EPs and barlow for the price of one XW EP. Not that I would refuse XW 3.5mm.
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    That's a very interesting report, JG. Do you attribute the difference in resolution on M53 simply to the condensation of the cluster?

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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Nice shootout between the two EPs on the globs, JG!
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Nice report JG.

    Thanks for sharing the information.

    Clear skies.
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    Default Re: Barlowed BCO 6mm against the Pentax XW 3.5mm on the globular clusters M53 and M3

    Quote Originally Posted by Bigzmey View Post
    Thanks for the shootout JG! I am a big fun of BCOs to as you know. Except as you highlighted small FOV and short eye relief make using orthos with manual mounts somewhat challenging. Baader Q-turret is a nice solution to the problem: target with 32mm Plossl and flip to 6mm BCO. All set with EPs and barlow for the price of one XW EP. Not that I would refuse XW 3.5mm.
    Hello Bigzmey,

    there are at least 2 Pentax XW EPs, which can be hardly replaced with other makes on two simultaneously applicable reasons:
    - 70° AFOV when needed to frame the object
    - the unmatched high transmission of light in blue and blue/violet if compared with other wide field EPs, and as needed for the galaxies and globular clusters,
    and these EPs are the 3.5mm and 7mm in the Pentax XW series.
    At the 10mm and longer, there are lots of other EPs to select from.
    The 20mm up to 25mm is another story, but with similar requirements.

    Thank you for your comments,

    JG
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