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Thread: Eyepieces - Less glass is more

  1. #26
    Member Marko's Avatar
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    Alvin: Your link is a wonderful page but it is not your 'high glass' study, it is a bunch of hicksons. Nice page but not on point. I know you have a great study on the issue but it may be some other link on your awesome website I think.

    Lou: The reason Alvin started the reply with LOL on the other thread you linked to here is that Alvin is from what I have seen the #1 proponent of the virtues of eyepieces with as few lenses as possible. His comment on 'high-glass eyepiece' only refers to the Naglers and Ethos in that those designs have quite a few elements and not so much because they have a wide field of view.

    The argument is the more glass surfaces, the more loss of signal from light hitting discontinuities and leading to reflection and interference loss and it all adds up.

    The Zao-II are 'best of the best' and extremely rare and as such extremely expensive on a cost per gram of 'glass' ;-)
    Others that have come up include SuperMonocentric eyepieces that are a very basic and extremely low lens count eyepiece.

    It is for the reason that Alvin has studied this so much that I seek his expertise and opinion on this issue from time to time.
    Let me roam the deep skies and I'll be content.
    Mark Johnston
    18" StarMaster f/3.7
    12" Meade LightBridge f/5

  2. #27
    Member PeterN's Avatar
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    How do the Delos eyepieces stack up against these simpler eyepieces? I like the big eye lens and 20mm eye relief of the Delos. What about Brandons? Brandons have great contrast, but I'm not sure of the light transmission level. I use both of these.

    Quote Originally Posted by FaintFuzzies View Post
    On the other hand, at GSSP 2009, five observers, including Jimi and I saw the difference between the ZAO-II, UO HD and Ethos (all 6mm) in my 22". The UO HD is between the ZAO-II and Ethos, but a little closer to the ZAO-II in light transmission and the ability to perceive additional detail. Jimi and I agreed that the difference between the ZAO-II and the Ethos is obvious. Lastly, one of the five was a beginner and even he saw the difference.

    One of the object we were looking at was the triple galaxy system, NGC 6745 in Lyra.

  3. #28
    Member Preston Pendergraft's Avatar
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    Okay, I find all the optics and less glass is more idea interesting, and believable too. But I have one question for you fast dob owners. How much light do you lose from the Paracorr? I understand fast mirrors are necessary since you gotta transport a scope, but if you were looking at a observatory setting, would you consider going with a slower mirror such as f/5 ? The dobs I have owned were f/4.5 and f/6. At f/6 I didn't feel I needed a Paracorr. But it was a 10in scope, a 20in at f/6 would be huge.
    Last edited by Preston Pendergraft; June 9th, 2013 at 03:00 PM.
    Preston
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  4. #29
    Member lamperti's Avatar
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    Paracoor light loss ?

    Preston,
    I have used Paracorrs for most of my observing years with f4.5 dobs and never once considered light loss. My main concern was for optimizing the observing experience and having objects and stars sharp to the edge. I figured might as well get the best experience possible. I found that I did not need a Paracorr with a 20" f5 dob but now am back again with a faster 22" f4.2 telescope. The effective f now is 4.8.
    Whether transporting or having the telescope in an observatory, longer focal ratios also mean taller ladders.

    Quote Originally Posted by Preston Pendergraft View Post
    Okay, I find all the optics and less glass is more idea interesting, and believable too. But I have one question for you fast dob owners. How much light do you lose from the Paracorr? I understand fast mirrors are necessary since you gotta transport a scope, but if you were looking at a observatory setting, would you consider going with a slower mirror such as f/5 ? The dobs I have owned were f/4.5 and f/6. At f/6 I didn't feel I needed a Paracorr. But it was a 10in scope, a 20in at f/6 would be huge.

  5. #30
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    Being a bit dated in some respects I have 6, 10, 16, and 25mm Clave plossls which I often use with a Clave Barlow, but on planets without the Barlow for max light transmission . Though over 30 years old they can still hold up well against many newer designs, though I sill like my Naglers and other wide fields.

  6. #31
    Member Marko's Avatar
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    The thread is digressing a bit but my main reason for 18" f 3.7 was no ladder at zenith and I love that advantage to this day. I zip around with fewer obstacles. When I go high mag which is how I tend to use the 6mm or 8mm eyepieces I am mostly only caring about the middle of the field as this is typically for tiny objects. I often take out the Paracorr for going real deep as it turns out the need for it is mostly for when you are using more of the light cone like 16mm or more. So I take it out and as such light loss (whatever it may be) is out of the picture (literally). I'm no expert on this but that is what I have heard and it seems reasonable. Everything is a tradeoff. If I only used it in a fixed location your argument seems reasonable and sure, 4.8 would offer a better view. For me, a ladder in the van is one more piece of stuff in there and one more thing to forget and be real sorry I forgot.
    Last edited by Marko; June 23rd, 2013 at 08:21 AM.
    Let me roam the deep skies and I'll be content.
    Mark Johnston
    18" StarMaster f/3.7
    12" Meade LightBridge f/5

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