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Thread: Looking for EP advice

  1. #1
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    Default Looking for EP advice



    Greetings again. It is I.

    I am half overjoyed at seeing your friendly physiognomies again. (+thanks for anyone who gets THAT movie reference...)

    I am recently the owner of a new Skyline 10" dob. Prior to that, I operated a somewhat dinged and used Orion 130ST. My first experiences with the big dob are awesome. It came with a 2" 30mm Erfle EP that seemed well matched to the telescope. The images were clean almost all the way across the whole lens. After viewing through this combination for some time, I switched to one of my older EP's, an Orion Expanse EP (20mm) I was less than impressed, which is odd considering in my old telescope I was very satisfied with the performance of these, but in the dob the image was only good towards the center of the lens, and the further out from center the subject got the worse the image became. I quickly put the Erfle back in the scope and stared suspiciously at my EP case the rest of the evening.

    It occurs to me, for reasons of aperture, focal length and speed, or whatever sorcery otherwise may be at play, that not all EP's will perform the same from telescope to telescope. Most of you here I imagine already know this. That's why I'm here.

    I need good advice on EP's well suited to my new telescope. I didn't spend 600 bucks on it to produce mediocre images for me. But at the same time, I did just spend 600 dollars, so I can't afford to get my wallet raped again for new EP's. I'm looking at the 2" offerings from Orion, their Deepview and Q70 EP's. Anybody have any experience with these? Will they not produce an image on the outer half of the lens that looks like it was made of cellophane? Is there something better out there, in a similar price range?What focal lengths besides a 30mm would you include in your eyepiece case? Also what's your experience with EP's that come in a barrel that fits both 1.25 and 2" focuser? To me it seems they'd just be 1.25" EP's...

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    Default Re: Looking for EP advice

    The Q70s do not perform well in a fast Newtonian, only the center of the EP will be clear.

    The 1.25/2" EPs are just 1.25" that will also fit in a 2" focuser, but still just 1.25".

    I recommend you seriously look at ES 82s and/or 68s if you want the best view possible without spending a significantly higher amount per EP. They perform very well in a fast Newt and are the best value (IMO) on the market today.
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    Default Re: Looking for EP advice

    I agree with the above recommendation. The ES 68 degree line can be found used to save you some cost. The old green barrel Meade 68 degree line are also decent performers, although their slightly lower used prices reflect their slightly lesser performance. Still if the price is right, you won't be disappointed. If you search this forum and others for "Orion Expanse" and "Expanse clones", you will see comments that back up exactly what you have observed. The perimeter of the field in the 20 and 15 gets progressively poorer as you move to faster ratios, and even in slow scopes they are only "good" in the central areas. When they first came out they were the first eyepieces with a 66 degree field at their price, but they also ignited the debate of whether you are better off with a clean narrow field or a messy wide perimeter which allows you to find objects easier in a push Dob, even though much of the field is unusable. This is frequently discussed here because now at all price points you have this choice and eye relief also seems to go hand in hand with a wider field usually having a tighter fit.
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    Default Re: Looking for EP advice

    You are correct EPs that fit both 1.25" and 2" barrels are just 1.25" EPs.

    You should not go above 30mm in your 10" DOB, so if your 30mm Erfle works you don't need to worry about extra 2" EPs. Generally, you would want to space your EPs 1.3-1.5x a part. So something like 30mm - 20mm - 15mm - 10mm - 7mm should work.

    Orion EPs do not offer best value, they tend to be overpriced for their performance as you already found out with your Expanse.

    I would second Ozman's advice on Explorer Scientific 82 and 68 degree EPs. If that a bit to pricey my second suggestion is Celestron X-Cel LX.
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    Scopes: Celestron: 8" SCT F10, Omni 150R Achro F5, Onyx 80ED F6.3; ES: 127mm CF F7.5 APO. Mounts: ES Twilight I, Bresser EXOS2, SW SkyTee2, UA MicroStar. Binos: Orion 10x50, Celestron 8x42. EPs: TeleVue: Plossls & barlows; ES: 82os & 68os; Vixen: SLVs & NPLs; Baader: BCOs & Aspherics; EO/UO: HD Orthos; Meade: UWAs & Plossls; Celestron: X-Cel LXs, Luminos; GSO SVs. Filters: Astronomik: UHC; Lumicon: OIII, H-beta, DeepSky; Baader: UHC-S, M&SG, CB; Orion: UltraBlock, SG. DSO tally: 916 (H400-1: 400, H400-2: 139, H300-3: 26; M110: 110, S110: 67). Doubles: 592, Comets: 5, Asteroids: 26
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    Default Re: Looking for EP advice

    What is the issue with Erfles, that I don't see many for sale? Or do they go by some other less user-friendly name?

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    Default Re: Looking for EP advice

    They are an older design. They perform well if used for what they were designed for in a long refractor or cassegrain scope, but some newer designs perform better in a wider range of scopes.
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    Default Re: Looking for EP advice

    They are still around, Orion Q70 and GSO SuperView are Erfles. As Ozman indicated they perform better in slow scopes and under low powers.

    There are also some designs which are trying to address Erfle weaknesses (soft focus and field curvature) by adding extra lenses. Baader Hyperion line is a good example.
    Scopes: Celestron: 8" SCT F10, Omni 150R Achro F5, Onyx 80ED F6.3; ES: 127mm CF F7.5 APO. Mounts: ES Twilight I, Bresser EXOS2, SW SkyTee2, UA MicroStar. Binos: Orion 10x50, Celestron 8x42. EPs: TeleVue: Plossls & barlows; ES: 82os & 68os; Vixen: SLVs & NPLs; Baader: BCOs & Aspherics; EO/UO: HD Orthos; Meade: UWAs & Plossls; Celestron: X-Cel LXs, Luminos; GSO SVs. Filters: Astronomik: UHC; Lumicon: OIII, H-beta, DeepSky; Baader: UHC-S, M&SG, CB; Orion: UltraBlock, SG. DSO tally: 916 (H400-1: 400, H400-2: 139, H300-3: 26; M110: 110, S110: 67). Doubles: 592, Comets: 5, Asteroids: 26
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    Default Re: Looking for EP advice

    Quote Originally Posted by Bigzmey View Post
    They are still around, Orion Q70 and GSO SuperView are Erfles.
    It would seem by appearance I already have a GSO Superview, or a reasonable facsimile thereof, separated at birth. The SkyLine 30mm I have is a dead ringer. Makes sense, as i believe the Skyline I have may be a re-branded GSO. I did some Googling on these last night and read that any two GSO's can be as different as night and day regarding quality. Either they've tightened up quality control since those comments were written or I've been lucky in bagging a superior one.

    Quote Originally Posted by Trombatissimo View Post
    If you search this forum and others for "Orion Expanse" and "Expanse clones", you will see comments that back up exactly what you have observed. The perimeter of the field in the 20 and 15 gets progressively poorer as you move to faster ratios, and even in slow scopes they are only "good" in the central areas. When they first came out they were the first eyepieces with a 66 degree field at their price, but they also ignited the debate of whether you are better off with a clean narrow field or a messy wide perimeter which allows you to find objects easier in a push Dob, even though much of the field is unusable.
    I took this last statement into consideration last night when I hauled my scope out of the garage again. With Jupiter on the rise offering suitable subject matter, I decided to have a little EP "shootout" right in my back yard: The Orion Expanse 6mm vs. a Celestron Omni 6mm Plossl that I have. What I took from your statement without any reliable way to measure, is that perhaps both may offer similar usable FOV's, but the Expanse seemed to have a clear advantage in brightness and clarity with the image centered, not to mention the eye relief was alot more comfortable. On some of these cheap short focal length EP's I find looking into them is akin to some Saturday morning cartoon cat looking for his antagonist, in doing so has to push his entire eyeball through a hole in the wall only to have it poked out. So, I suddenly don't feel so bad about having the Orion's in my kit, clearly though an upgrade is probably still in order. Thanks for the advice all, I'll probably be looking into the ES offerings in the very near future.
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