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Thread: EP opinions for large nebula and open clusters

  1. #1
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    Default EP opinions for large nebula and open clusters



    Good evening Ladies and Gentlemen, I am looking for some opinions on the best mm for observing larger nebula and some open clusters.
    What has worked well for you? The telescope I will be using is the Orion XT12g. F.L 1500 F.R f4.9
    Telescopes: Orion XT12g, Celestron Omni XLT 102mm

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    Default Re: EP opinions for large nebula and open clusters

    Hi Brian!

    In my experience, you want the widest field possible, and that means low power. And with a reflector, this also means you want to strike the proper balance between exit pupil and the TFOV. Too large of an exit pupil and you get the dark shadow of the secondary mirror showing up in the view and you can lose some light.

    There are several great threads on the topic. Here is a good example: How do you determine what EPs or Power to use for DSO viewing?

    I've found that my ES 82° 30mm is a great low power wide-field eyepiece in my dob (FL 1520mm, f/5), but I do lose some light due to the larger exit pupil, especially noticeable on brighter objects, and the secondary shadow is evident. The ES 82° 24mm is much better in this regard in my dob.

    This very thing that you are asking about is one of the big factors in my purchasing of the AR127 and ST80 refractors. The main function of these two scopes for me is larger nebulae and big spread out open clusters.

    That doesn't really help you immediately on an eyepiece to choose, but it should hopefully give you some direction of study to help you make a better decision. I'll shut up and turn it over to the smart folks who can offer better opinions than mine.

    More reading:

    A Pupil Primer - Sky & Telescope
    Bryan

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    f/5; Celestron C6-R f/8; ES AR127 f/6.4; ES AR127 f/9.4; Stellarvue SV102T f/7; ES AR102 f/9.8;
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    Default Re: EP opinions for large nebula and open clusters

    Thank you Bryan, the 2 largest that I have are 28mm and 32mm. I never really took the time to do the math and figure out anything other than magnification. Looks like I need to do some research and find what tfov and exit pupil I have and would like to try.
    Telescopes: Orion XT12g, Celestron Omni XLT 102mm

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    Default Re: EP opinions for large nebula and open clusters

    The ES 100* 20mm would also be a good choice for larger targets in a Dob. The 100* EPs are a good bit pricier than the 82* EPs, but that huge FOV is pretty awesome. My 82* 30mm is also an awesome EP, nice sharp views right out to the edge.
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    Celestron Powerseeker 114az "Little Tyke", CPC 1100 GPS “Big Daddy 2.0”
    ES82 30mm, 6.7mm, 4.7mm; Tele Vue Delos 17.3mm, 12mm; Tele Vue DeLite 9mm; Meade UWA 14mm; Assorted Budget EPs
    ES 2" 99% Dielectric Diagonal

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    Default Re: EP opinions for large nebula and open clusters

    Well I finally got around to figuring all this up. For my scope 5mm is the highest useful magnification and 32mm is the lowest. All of the ones I have are over 1 and under 7 exit pupil. Maybe I need to invest in better filters as well like OIII, dark sky and UHC?
    Telescopes: Orion XT12g, Celestron Omni XLT 102mm

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    Default Re: EP opinions for large nebula and open clusters

    Quote Originally Posted by ruger4d4 View Post
    Well I finally got around to figuring all this up. For my scope 5mm is the highest useful magnification and 32mm is the lowest. All of the ones I have are over 1 and under 7 exit pupil. Maybe I need to invest in better filters as well like OIII, dark sky and UHC?
    I think a filter or two would be a wonderful addition to your arsenal. A nice OIII and a narrowband UHC would fit the bill nicely for you.

    I would consider these:

    The DGM NPB: Order USA You can ask for pricing on the "seconds", as these are purportedly optically sound, yet come with a price reduction. This filter gets excellent reviews. It is next on my filter list.

    The Orion Ultrablock: 2" Orion UltraBlock Narrowband Eyepiece Filter | Orion Telescopes

    Baader OIII: Baader O-III Nebula Filter - 2" # FOIII-2 2458396

    For the budget minded with larger aperture, the Zhumells are decent enough for the cost: https://www.telescopesplus.com/colle...ope-filter-set
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    Bryan

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    f/5; Celestron C6-R f/8; ES AR127 f/6.4; ES AR127 f/9.4; Stellarvue SV102T f/7; ES AR102 f/9.8;
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    Default Re: EP opinions for large nebula and open clusters

    My method for locating DSOs(nebula) is to use a wide FOV and then step down once located or if needed to identify.
    Once located, I choose an EP that will best frame the DSO as it relates to the DSO size.

    Here's a laminated chart I keep taped to the scope (The upper left relates to optics: magnification and TFOV).
    No sense ruining a clear night under the stars doing math.

    OpticsChart.JPG
    - Rick
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    Default Re: EP opinions for large nebula and open clusters

    I second the DGM NPB filters. I bought the cosmetic seconds. Optically fine. No Issues. I have to yet to determine what the 'cosmetic' issue on mine is as it looks perfectly intact and of great quality.
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    - Rick
    Astronomical League Member-At-Large
    Scopes: Zhumell Z10, Explore Scientific AR152, Celestron 8SE, Meade Infinity 80
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    Filters: DGM NPB, Lumicon OIII Binoculars: Apogee 25x100, Oberwerk 9x60, Gordon 10x50

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    Default Re: EP opinions for large nebula and open clusters

    Oh wow, I have never heard of this place. Thanks Bryan!
    Telescopes: Orion XT12g, Celestron Omni XLT 102mm

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    Default Re: EP opinions for large nebula and open clusters

    Quote Originally Posted by rickg18704 View Post
    My method for locating DSOs(nebula) is to use a wide FOV and then step down once located or if needed to identify.
    Once located, I choose an EP that will best frame the DSO as it relates to the DSO size.

    Here's a laminated chart I keep taped to the scope (The upper left relates to optics: magnification and TFOV).
    No sense ruining a clear night under the stars doing math.

    OpticsChart.JPG
    I absolutely love this idea! I will definitely have to borrow this idea. Thanks Rick!!
    Telescopes: Orion XT12g, Celestron Omni XLT 102mm

 

 

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