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Thread: Some eyepiece questions.

  1. #1
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    Default Some eyepiece questions.



    I've been doing a lot of reading on eyepieces, but I'm starting to get confused. Some people talk about an eyepiece by magnification and some people talk about them by pupil diameter. Is this two different ways of figuring out the same type of information or is one way better then the other for determining roughly what you want to use? For example I read a post where people were talking about what pupil size they like to use for different messier objects or planets, and then another post where people were saying I use a 5.5mm which gives me 200x magnification to look at jupiter.

    Another question I have is... I noticed alot of people try to steer others away from getting the 5mm range eyepieces because they say you need really good viewing conditions to use an eyepiece like this. I also notice alot of people talking about using these smaller focal length eyepieces. I guess what I'm getting at is are the posts I'm reading where people are saying not to get one just trying to steer beginners away from thinking that they need to max out their scopes right off the bat, or are these sizes really not used too much?

    Last question... I just purchased a used z10 dob. It comes with the stock zhumell 9mm plossl and 30mm wide angle eyepieces. I'm new to telescopes, and I'm not planning on buying a bunch of eyepieces till I get use to using it ( maybe in a year or so), but I do wear glasses for astigmatism. It's not too bad, but I'd prefer to be wearing them if I could. So I've been considering getting the 9mm version of either the meade hd 60 or Cele version of it which people say are cheaper. First off would these give me enough eye relief for glasses? Second of all is sticking with 9mm a good size to stick with? If I am understanding things right it would give me 1.8mm pupil size or 139x.
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  2. #2
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    Default Re: Some eyepiece questions.

    My neighbor has astigmatism and is using TeleVue eyepieces (de-lite) with his correcting lenses. It's working well for him.
    My eyes
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    Default Re: Some eyepiece questions.

    For now, don't pay attention to exit pupil. It's simply the relationship of the focal length of the scope and eyepiece focal length.
    If you really need glasses, you need eyepieces with 16mm or greater eye relief.

    To start you need 3-4 eyepieces. Low power around 60x, medium power around 100x, a medium high power around 160x, and for those occasions when the atmosphere allows for it a high power between 200 - 240x.

    The next thing most pay attention to is apparent field of view. You should look for a minimum of 68°. The exception is for viewing planets where it doesn't matter so much.

    Cheaper eyepieces will show coma ( stars look like comets ) towards the edge of the field of view. The better eyepieces tend to be much better, the best eliminate all together.

    Most would agree the best affordable eyepieces are from Explore Scientific. The do however make a few that are quit expensive.

    Scott
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    Default Re: Some eyepiece questions.

    Quote Originally Posted by gcnadam2906 View Post
    Another question I have is... I noticed alot of people try to steer others away from getting the 5mm range eyepieces because they say you need really good viewing conditions to use an eyepiece like this. I also notice alot of people talking about using these smaller focal length eyepieces. I guess what I'm getting at is are the posts I'm reading where people are saying not to get one just trying to steer beginners away from thinking that they need to max out their scopes right off the bat, or are these sizes really not used too much?
    Imagine your eyepiece is like the resolution setting on your computer monitor. Run a game at say 1900 x 1020 - This would be say a 25mm eyepiece. Things look sharp, a little small, but still worth the effort. Now drop that game down to 800 x 600 - Thats going to give the same effect as a 5mm. You are basically spreading the same amount of light over an ever increasing area, things get blurry unsteady etc.

    The second thing is take a little time to see what interests you observing wise. If open clusters are your thing, low powered wide field eyepieces are the way to go. If planets and double stars get you interested, then start thinking about those higher magnification eyepieces.
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  5. #5
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    Default

    Quote Originally Posted by MG1692 View Post
    Imagine your eyepiece is like the resolution setting on your computer monitor. Run a game at say 1900 x 1020 - This would be say a 25mm eyepiece. Things look sharp, a little small, but still worth the effort. Now drop that game down to 800 x 600 - Thats going to give the same effect as a 5mm. You are basically spreading the same amount of light over an ever increasing area, things get blurry unsteady etc.

    The second thing is take a little time to see what interests you observing wise. If open clusters are your thing, low powered wide field eyepieces are the way to go. If planets and double stars get you interested, then start thinking about those higher magnification eyepieces.
    That is pretty much my plan overall. I was just considering replacing the 9mm that comes with it with something I could use with my glasses, but I could just deal with not using my glasses for that size until I figure out what I prefer to look at.

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    Default Re: Some eyepiece questions.

    I have an amazing vintage Vixen 5mm Ortho that I use quite often on my 1200 mm fl Refractor. There are many times when the upper atmosphere is more than steady to view Planets with it. I'm glad I have it for those nights and would highly recommend having at least one in this range for these occasions if you have a scope of this design. Orthos are very inexpensive as well. They do have limitations such as short eye relief but the view when the night is perfect more than makes up for it.
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    Default Re: Some eyepiece questions.

    To start off inexpensively, the Celestron X-Cel LX eyepieces (EPs) all have 16mm eye relief and provide excellent sharp views. For a sub $60 EP they are hard to beat. I have four of them (plus other more expensive EPs) and the X-Cels get used all the time.

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    Default Re: Some eyepiece questions.

    In addition to optical properties of telescope/EP combo one need to take into consideration atmospheric conditions. My 8" scope is capable of 400x, but on many nights I can't push it above 100x due to bad seeing. Since you already have 9mm (139x) and 30mm (42x) I would suggest to get 12mm LX X-Cel which will give you 104x. LX X-Cel are great performers and very comfortable to use with glasses ( I have a very complex prescription )

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    Default Re: Some eyepiece questions.

    The X-Cel LX 9 and 12mm EPs are both excellent options for their price range, and I've used both comfortably with glasses on several occasions although I normally observe with my contacts in.
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