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Thread: Beginner questions - eyepieces for astro master 130EQ

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    Default Beginner questions - eyepieces for astro master 130EQ



    Hi everyone,

    I am new to this forum. Just joined couple days ago and I just purchased a telescope ( celestron 130 EQ ). I know that most of the information I am about to ask here is probably somewhere in this forum but it would be great if someone can help me over here since I am a beginner and some of the already existing threads out there are a bit too technical for me :

    1. what is the difference between buying a zoom eye piece ( for example 8 mm to 24 mm ) vs buying few individual eye pieces within that range ? for example, is there a a decrease in image quality in viewing through a zoom eyepiece set at 10mm vs viewing through a fixed 10 mm eye piece ?

    2. On Thursday I ordered a couple of plossl eyepieces as I read that the 10mm and 20mm eyepieces that came with my telescope are not very good. does anyone have any suggestions what types of eyepieces I can use with the astromaster 130EQ ? since yesterday I was able to see Mars and Jupiter ( after multiple tries since I am currently struggling just pointing the telescope at the right place ) but they seem bright and I assume too many reflections . would a better eyepiece fix that issue or should I also get some sort of light filters ?

    3. what is the difference between using a 2x barlow and a 20mm eyepiece vs using a 10 mm eyepiece ? (since both should give me the same zoom specs of 10 mm) . is there any loss in quality when using a 20 mm eyepiece with a 2x barlow vs directly using a 10 mm eyepiece ?

    4. On the celestron website, my telescope is supposed to have a highest useful magnification of 307X. what is the limit I should be refraining from in order not to lose much image quality ? for example , if I understood correctly, a 2X barlow and a 6 mm eyepiece would give me roughly 216 magnification. Would this be a safe margin in terms of not losing quality since 216 is well below 307


    once again I apologize in advance since most of these questions are probably receptive to most of you guys but it would be good if someone can explain to me in simple terms and in a not too technical manner


    thanks,

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    Lowjiber's Avatar
    Lowjiber is offline Urban Astronomer
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    Default Re: Beginner questions - eyepieces for astro master 130EQ

    Welcome to the forum.

    As I started this reply, I see that there have been ten views and no responses yet, so I'll take a crack at it.

    Quote Originally Posted by mruhomau View Post
    ...
    1. what is the difference between buying a zoom eye piece ( for example 8 mm to 24 mm ) vs buying few individual eye pieces within that range ? for example, is there a a decrease in image quality in viewing through a zoom eyepiece set at 10mm vs viewing through a fixed 10 mm eye piece ?

    Unless you're talking about a premium zoom, say a Baader Clickstop, there is a very slight degradation with a zoom verses a "fixed" eyepiece. However, it takes a very discerning eye to notice. Don't worry about that.

    The major difference with a zoom eyepiece is that as the focal length of the setting gets shorter (toward 8mm) the field of view gets wider. At the maximum focal length (24mm) the FOV is the narrowest. That is opposite "fixed" eyepieces with which the FOV is wider when the focal length is longer... that's why we hunt DSOs with say a 24mm "fixed" eyepiece. No big deal, but you asked.


    2. On Thursday I ordered a couple of plossl eyepieces as I read that the 10mm and 20mm eyepieces that came with my telescope are not very good. does anyone have any suggestions what types of eyepieces I can use with the astromaster 130EQ ? since yesterday I was able to see Mars and Jupiter ( after multiple tries since I am currently struggling just pointing the telescope at the right place ) but they seem bright and I assume too many reflections . would a better eyepiece fix that issue or should I also get some sort of light filters ?

    You don't need any filters to observe planets (with one exception below), although some folks prefer a #890A Blue filter to enhance Jupiter a bit.

    The only planet you might consider using a variable polarizing filter to view would be Venus. Venus is very bright, and to see its phases, one needs to dim it down a bit.

    You are correct, in that the eyepieces that come with scopes in that price range are not the best... by a long shot. However, you don't need eyepieces that start around $150 each to enjoy that scope. A standard, major brand plossl eyepiece will do the job for you. I'll mention that the Zhumell Planetary Series eyepices are pretty darn good and reasonably priced.


    3. what is the difference between using a 2x barlow and a 20mm eyepiece vs using a 10 mm eyepiece ? (since both should give me the same zoom specs of 10 mm) . is there any loss in quality when using a 20 mm eyepiece with a 2x barlow vs directly using a 10 mm eyepiece ?

    There is no real difference in quality of the view. Even with an inexpensive barlow like the Orion Shorty 2x, you'll have no degradation of viewing.

    There is actually an advantage to using a barlow if you observe wearing glasses. With a couple of exceptions (Baader Hyperions for example), the eye relief is at its max with the longest focal lengths, and slowly becomes less as one changes eyepieces to shorter focal lengths. With a barlow installed, the eye relief of the accompanying eyepiece is retained... handy if you're wearing glasses.

    4. On the celestron website, my telescope is supposed to have a highest useful magnification of 307X. what is the limit I should be refraining from in order not to lose much image quality ? for example , if I understood correctly, a 2X barlow and a 6 mm eyepiece would give me roughly 216 magnification. Would this be a safe margin in terms of not losing quality since 216 is well below 307.

    Forget you ever read that 307x number. It is doable if you're on top of a 3,000 ft mountain and looking through perfect skies at a target near zenith. 200x is about your max, and then only on targets above 30 degrees on a night where the "seeing" is almost perfect... maybe twice a year. Of course, like most "rules" in this game, there is an exception... on a decent night, one can pump the power up above 200x when viewing the moon. (You can darn near observe the moon through a Coke bottle.

    Before you start going "barlow crazy" let's take a look at a couple of numbers...

    Your scope has a focal ratio of f/5. That's the ratio of your scope's focal length to its diameter. Scopes f/5 and lower are what we lovingly call "fast". Fast scopes are very sensitive to an accurate collimation. I'll bet dollars to dog biscuits you haven't collimated that scope... that's likely why you see that extra light you mentioned earlier. If you want to see "the bible of collimation" it's here:Astro Babys Guide to Collimation

    Remember that f/5 number? It's the most important number you'll ever need with that scope. You should never (moon excepted) even consider using an eyepiece and/or eyepiece-barlow combination that has a focal length less than the focal ratio of your scope... period. Even with an eyepiece combo of 5mm, you'll only be able to use it (again, moon excepted) on those handful of sessions where the "seeing" is extraordinary.

    You see, as magnification increases, target surface brightness decreases.

    Keeping that in mind, it a general "rule-of-thumb" that the optimum combination of magnification and surface brightness is obtained with an eyepiece that has a focal length equal to two times the scope's focal ratio, expressed in millimeters. (Don't argue with that... you'll lose.)

    So, what does all that mumbo-jumbo mean? Simply that your maximum usable power is attained with an eyepiece that has a focal length of 5mm... that's 130x in your case. In general, your optimum, usable power will be with a 10mm eyepiece (twice your focal ratio)... 65x in your case.

    Now, before you get all excited, let me say two things...

    1. This game is not about magnification in most cases. It is about gathering photons... not so much with planets, but definitely with deep space objects.

    2. I'm not saying not to "push" your scope. We do it all the time. However, when you do just realize that you are asking it to do something that is not going to give you the kind of views that I think you expect.


    Once again I apologize in advance since most of these questions are probably receptive to most of you guys but it would be good if someone can explain to me in simple terms and in a not too technical manner.

    No need to apologize. We've all been there, done that.

    ...
    Note: I'm not going to edit the above reply. It's 110 deg F right now and I'm sitting outside.

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    John (Urban Astronomer)
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    Default Re: Beginner questions - eyepieces for astro master 130EQ

    hey John - thank you so much for that response. It was very informative and I understood 99% of it. I will re-clarify the remaining 1% in a bit lol. But Before let me somehow "introduce " myself. I am currently in Arizona visiting my in laws for a limited period of time ( visiting from Toronto ). My wife gave me a telescope for my bday last week since it was my childhood dream to have one ( being able to look at planets etc ) So once I was able to see saturn yesterday I got all super excited and has since been trying to browse about eyepieces and barlows etc. So good thing you sent me this response because this will for sure save me a lot of $ in buying things that would simply push my telescope too far ( more than the 5 mm theory focal length you mentioned )

    so just to re-clarfy couple of things that you mentioned and I did not 100% understand :

    1.
    " The major difference with a zoom eyepiece is that as the focal length of the setting gets shorter (toward 8mm) the field of view gets wider. At the maximum focal length (24mm) the FOV is the narrowest. That is opposite "fixed" eyepieces with which the FOV is wider when the focal length is longer... that's why we hunt DSOs with say a 24mm "fixed" eyepiece. No big deal, but you asked. "

    so does that mean the variable zoom has a wider view when its at 8mm and a smaller view when its at 24 mm ? which is basically the opposite of fixed eyepieces ?


    2. what are deep sky objects ? are they objects that cannot be seen with the naked eye but the telescope will pull to be viewable in the eyepiece ?

    3. ( I know I said a couple but just a 3rd one ) based on your explanation of the focal ratio, does that mean telescopes with bigger diameters will have a higher usable magnification? if yes, then does that also mean telescopes with bigger diameters are more " usable " in not so clear skies ?


    You are 101% right about the collimation. I did not do anything . I "heard " and read about it online, but after 2 lines I got shyed away from it and chose to ignore it hoping that my telescope will be delivered perfectly collimated/aligned. lol . The issue is that bright objects don't seem to focus well and they are not that symmetrical. Saturn was "ok" but Mars was pretty much unviewable. (FYI I did not even know that planets were viewable from the naked eye as stars . There are some online webpage etc that showed yesterday in Arizona Mars and saturn were close to the moon. Pointing and aligning my telescope was not easy since its on an EQ mount. I don't know what I did but after 15-30 mins and aimlessly viewing ( since i cant use the red dot finder properly or don't know how to use it ) I was able to see saturn in my scope and then gradually moved to the moon and then finally Mars. And had to take a break after seeing Mars for 10 seconds as i ended up sweating since I was performing acrobatics in 100+ F temperature lol )

    Anyway , I am seriously thinking of collimating my telescope now. Maybe on a day that I have at least few hours before sunset. I did not yet read the link you pasted above , but which tool should I buy ? From what I saw on the celestron website, there is a simple collimation tool. Also when you say that my scope is sensitive to collimation, does that mean bigger scopes are easier to collimate compared to fast scopes ? ( I guess I just asked a 4th question lol )

 

 

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