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  1. #1
    oliross100's Avatar
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    Default Scope Eyepieces - Reccommendations please!



    Hi there,

    I'm just starting out in Astronomy, and have purchased this Celestron spotting scope;

    Ultima 100 - 45 Spotting Scope (item #52252) / Ultima Refractor Series Spotting Scopes / Spotting Scopes / Products / Celestron.com

    I got it for a bargain on ebay and I'm very excited to try it out when the weather clears (gotta love English weather). The eyepiece is in the box but it was separate to the actual body of the scope, and I was wondering first of all if this means I can actually buy separate eyepieces for it, or the reason it's separate is simply because that's how it comes in the box and I will only be able to use that particular one.

    If it does mean I can change eyepieces, what would you all recommend I try? As I said, I'm just starting out so not really clued up on eyepieces, barlows etc..so some advice would be appreciated!

    Thanks!

    Oli

  2. #2
    carnevali's Avatar
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    Your eyepiece is a zoom EP of variable focal length from 24 mm to 8 mm, giving magnification powers between 22x and 68x. So, you probably don't need any other eyepieces. Check to see if the diameter of the eyepiece barrel that goes into the telescope is 1.25". If that's the case, then there are many eyepieces that you could purchase separately to add to your zoom. The telescope focal length is 540 mm, so if you get a 6 mm eyepiece that would give you 540/6 = 90x magnification. A 7 mm would give you 77x, etc.

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  4. #3
    oliross100's Avatar
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    Default

    Thanks carnevali, I'll give it a measure and see if I can adapt it to other eyepieces. I haven't tested the scope yet, but hopefully will tomorrow and will see how it goes! Excited!

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    carnevali's Avatar
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    Default

    I forgot to mention: some zoom EP (maybe all? I don't know) can be used with a Barlow lens. If yours can be used with a 2x Barlow (you might want to borrow a barlow to check), that would give you an additional range of magnifications from 44x to 136x with a single purchase of a 2x Barlow.

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    Ah yes, this is where my embarrassment is evident....as I'm fairly new to this, whilst I've heard of the many eyepieces, filters, telescope types etc, I don't actually know what a Barlow lense is/does - I've certainly heard of it, but all I know is that it's very very useful/important and helps a hell of a lot but thats about it....would you or anybody else mind indulging me?!

  8. #6
    carnevali's Avatar
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    Default

    I'm not knowledgeable about any technical details. If you're interested, other people in the Forum can tell you all there is to know about Barlows. The basic story though is this: it's a single eyepiece to which you can then attach any other eyepiece you have. You cannot use the Barlow lens by itself, but together with another eyepiece it halves the eyepiece focal length. So, for instance, if you use a 24 mm (focal length) eyepiece with a 2x Barlow the combination becomes a 12 mm eyepiece, resulting in doubling the magnification power (but the field of view becomes smaller). If you then swtich to say an 8 mm eyepiece, the combination becomes a 4 mm eyepiece, doubling the magnification of the 8 mm eyepiece. In your case, the zoom + Barlow combination should become a 4-12 mm zoom (instead of 8-24 mm), doubling all the original magnification powers of the zoom (but resulting in smaller field of views). Keep in mind that the higher the magnification the harder it becomes to get a sharp image in the field of view, so don't fall in love too soon with the idea of higher and higher magnifications. The highest you can get productively depends on the quality of the scope and the mount, as well as atmospheric conditions, air turbulence, and a host of other factors. I imagine that typically you should be able to use the full range of the 8-24 mm zoom you probably have, and occasionally push the power up to anywhere between 80x and 120x, with some other EP or Barlow.

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    Default

    Thanks Antonio, you say you don't know much of the technical details but that was very helpful, thank you.

    I might have a peruse of the forum and see what I can find regarding barlows and eyepieces in general.

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    Quote Originally Posted by carnevali View Post
    You cannot use the Barlow lens by itself......
    Hi Carnivali

    Did you know that you CAN use a barlow by itself..??
    (assuming the scope's focuser has wnough 'in-travel')

    Galileo's eyepieces were very similar to a modern barlow - You get an upright image, but with a VERY small field of view - it's a bit like looking down a pipe.
    A 2x barlow is roughly a 30mm eyepiece when used this way.
    You definitely wouldn't want to use barlows for eyepieces if you can help it though.
    I suppose for a small terrestrial target - say for instance, a distant bird on a telegraph pole - it could be useful for a quick look if you don't have an upright diagonal, or an 'erector' barlow - but VERY awkward to use for astronomy purposes.


    Give it a try - It really does make you appreciate what Galileo was up against, and can only make you respect him even more.
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    Quote Originally Posted by Carlos_dfc View Post
    Hi Carnivali

    Did you know that you CAN use a barlow by itself..??
    (assuming the scope's focuser has wnough 'in-travel')

    Galileo's eyepieces were very similar to a modern barlow - You get an upright image, but with a VERY small field of view - it's a bit like looking down a pipe.
    A 2x barlow is roughly a 30mm eyepiece when used this way.
    You definitely wouldn't want to use barlows for eyepieces if you can help it though.
    I suppose for a small terrestrial target - say for instance, a distant bird on a telegraph pole - it could be useful for a quick look if you don't have an upright diagonal, or an 'erector' barlow - but VERY awkward to use for astronomy purposes.

    So if a Barlow doubles an eyepieces power (20x eyepiece x 2x Barlow=40x) then 0x0=0.....not that great?
    Give it a try - It really does make you appreciate what Galileo was up against, and can only make you respect him even more.
    So if a Barlow doubles an eyepieces power (20x eyepiece x 2x Barlow=40x) then with no eyepiece 0x0=0.....not that great?
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    Carlos_dfc's Avatar
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    Quote Originally Posted by tglenn View Post
    So if a Barlow doubles an eyepieces power (20x eyepiece x 2x Barlow=40x) then with no eyepiece 0x0=0.....not that great?
    Hiya Tracy,
    It doesn't quite work like that.

    The doubling effect only happens if you use an eyepiece with the barlow...

    Without an eyepiece, the glass in the barlow itself will work like an eyepiece (kinda)
    The kind of eyepieces we are used to, create an image that appears to be just beyond the eye-lens...
    But Galilean-style eyepieces (and a barlow on it's own), create an image which appears to be a deep inside the scope.

    Experimenting with my Orion shorty barlow, it gives an effective focal length of around 30mm - or about 40x in my f/1200 Dob

    Admittedly, they are pretty useless as eyepieces when compared to a modern EP - but worth trying it out just once, to see the kind of views that Galileo used to get.
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