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Thread: Calculating EP focal lengths to build a balanced set

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    Default Calculating EP focal lengths to build a balanced set



    Hey guys,

    So the time to build my initial EP set has come and I am attempting to keep my EP budget to a reasonable (for me) level. I read on here a couple of months ago, an outstanding post detailing a formula/algorithm to achieve the best EP focal length spacings to get the most from your scope. I attempted to search the forum, including my own history, as well as Google and have not found anything. Perhaps I am using the incorrect phrasing/terminology? I could have sworn that I responded to the post and even suggested it become a sticky, but apparently not.

    Regardless, my budget allows the purchase of three to four EPs or three EPs and a Barlow, which is what Im leaning more towards at the moment, because that would essentially give me six focal lengths to choose from. From everything Ive read and seen, which has made my head spin at times, the EPs at the top of my list at the moment are the Baader Morpheus line. I have no idea where to start with Barlows but I do know I want a 2x or possibly a 2.1x. (Im open to suggestions here)

    My soon to be acquired scope is the ES ED102CF F/7 APO which will be used momentarily for observation and then used for AP primarily afterwards. I look forward to reading your responses. Thanks for reading!

    -Justin
    Oberwerk 11x70 and 15x70 binos
    Stellarvue 102 Access APO doublet
    Skywatcher NEQ6pro GEM
    GSO 2 Star diagonal
    Baader 6,10,18 Classic Orthos, 32 Ploosl, 1.3x and 2.25x Barlows
    Shoestring USB2EQ6 running ASCOM/EQMOD, Stellarium and CDC

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    Default Re: Calculating EP focal lengths to build a balanced set

    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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    Amici prism, 2" Stellarvue Dielectric, 2" TeleVue Everbrite
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    The weakest link in the optical chain is the large nut located directly behind the
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    Ya gotta keep this Apo/
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    thing in some balance of perspective. Apos are awesome, but long focus Achros aren't that far behind them - Siriusandthepup (CN)

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    Default Re: Calculating EP focal lengths to build a balanced set

    Quote Originally Posted by JustinG View Post
    Hey guys,

    So the time to build my initial EP set has come and I am attempting to keep my EP budget to a reasonable (for me) level. I read on here a couple of months ago, an outstanding post detailing a formula/algorithm to achieve the best EP focal length spacings to get the most from your scope. I attempted to search the forum, including my own history, as well as Google and have not found anything. Perhaps I am using the incorrect phrasing/terminology? I could have sworn that I responded to the post and even suggested it become a sticky, but apparently not.

    Regardless, my budget allows the purchase of three to four EPs or three EPs and a Barlow, which is what I’m leaning more towards at the moment, because that would essentially give me six focal lengths to choose from. From everything I’ve read and seen, which has made my head spin at times, the EPs at the top of my list at the moment are the Baader Morpheus line. I have no idea where to start with Barlow’s but I do know I want a 2x or possibly a 2.1x. (I’m open to suggestions here)

    My soon to be acquired scope is the ES ED102CF F/7 APO which will be used momentarily for observation and then used for AP primarily afterwards. I look forward to reading your responses. Thanks for reading!

    -Justin
    I used to have ED102CF which I traded in for ED127CF. I wish I could have keep both, it was a nice little scope.

    Anyhow, I would advice against Morpheus. The specs sound good on paper, but the execution is lacking. I tested one and sent it back, could not stand it.

    Your money would be better spend on TeleVue, Explorer Scientific, Vixen or Meade EPs. Depending on your preference for eye relief and FOV, we can point you right direction.
    j.gardavsky, DeanD and JustinG like this.

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    Default Re: Calculating EP focal lengths to build a balanced set

    Yes Gabby that is it!! Thanks a million
    Gabby76 likes this.
    Oberwerk 11x70 and 15x70 binos
    Stellarvue 102 Access APO doublet
    Skywatcher NEQ6pro GEM
    GSO 2 Star diagonal
    Baader 6,10,18 Classic Orthos, 32 Ploosl, 1.3x and 2.25x Barlows
    Shoestring USB2EQ6 running ASCOM/EQMOD, Stellarium and CDC

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    Default Re: Calculating EP focal lengths to build a balanced set

    They not only sound good on paper but several reviews Ive read showed promise, particularly the one on Cloudy nights when they were compared to Pentax XWs and Takahashi Abbes. My original list toppers were the Orion Stratus line which was then quickly replaced by the very similar Baader Hyperion line. I simply wasnt buying into the whole modular concept. In regards to AFOV, wider does sound more enjoyable but is not the end all be all. My experience with quality scopes and EPs is nil so I have no real frame of reference. Eye relief is not a major issue since I do not wear glasses but still seems like everyone strongly agrees that an eye relief between 15-20mm is the way to go. Like I said above, Im completely open to suggestions. I will be primarily viewing DSOs but something that performs well on planets and the moon would be nice too. I suppose Im looking for a decent balance of performance and price, as I assume we all do. My budget for EPs alone right now is $500-600 and I am hoping to be able to purchase 3-4 and perhaps a barlow as well. If my budget doesnt work without seriously sacrificing quality, then Ill have to revisit that. Thanks again guys!
    Oberwerk 11x70 and 15x70 binos
    Stellarvue 102 Access APO doublet
    Skywatcher NEQ6pro GEM
    GSO 2 Star diagonal
    Baader 6,10,18 Classic Orthos, 32 Ploosl, 1.3x and 2.25x Barlows
    Shoestring USB2EQ6 running ASCOM/EQMOD, Stellarium and CDC

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    Default Re: Calculating EP focal lengths to build a balanced set

    The best out of the bunch are the Vixen LVW that the Orion and Baader (Stratus and Hyperion) are both based on, you would have to look for them used though.
    I highly recommend those.
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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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    The weakest link in the optical chain is the large nut located directly behind the
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    Ya gotta keep this Apo/
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    thing in some balance of perspective. Apos are awesome, but long focus Achros aren't that far behind them - Siriusandthepup (CN)

    Refractors kick arse precisely because they don't hide behind excuses. That is, they have no obstructions to hide behind. - Jon Isaacs (CN)

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    Default Re: Calculating EP focal lengths to build a balanced set

    I certainly will Gabby. Thanks again for the link to your amazing post. I’m hoping I can find some
    Oberwerk 11x70 and 15x70 binos
    Stellarvue 102 Access APO doublet
    Skywatcher NEQ6pro GEM
    GSO 2 Star diagonal
    Baader 6,10,18 Classic Orthos, 32 Ploosl, 1.3x and 2.25x Barlows
    Shoestring USB2EQ6 running ASCOM/EQMOD, Stellarium and CDC

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    Default Re: Calculating EP focal lengths to build a balanced set

    Quote Originally Posted by JustinG View Post
    I certainly will Gabby. Thanks again for the link to your amazing post. I’m hoping I can find some
    Look on AstroMart for used ones. You can also put up a wanted listing.
    My eyes
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    Default Re: Calculating EP focal lengths to build a balanced set

    Astromart is great, I’m a bit put off by paying for classifieds however
    Oberwerk 11x70 and 15x70 binos
    Stellarvue 102 Access APO doublet
    Skywatcher NEQ6pro GEM
    GSO 2 Star diagonal
    Baader 6,10,18 Classic Orthos, 32 Ploosl, 1.3x and 2.25x Barlows
    Shoestring USB2EQ6 running ASCOM/EQMOD, Stellarium and CDC

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    Default Re: Calculating EP focal lengths to build a balanced set

    Quote Originally Posted by Gabby76 View Post
    There it is again! I like the efficiency of Set 2 since there is an ep very close to the 2mm sweet spot for contrast and resolution. When as in Set 1 that doesn't quite work out with the eps in the line one needs more eps to bracket the 2mm exit pupil as closely as possible. This leads to more eps in the set which is fine and reflected in the example. One can then make such a set's use more efficient by including a zoom to dial in the optimum exit pupil and then replacing the zoom with the closest fixed fl ep in the kit.
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