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Thread: astro-engineering barlow

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    Default astro-engineering barlow



    I recently received a omni xlt 120 for christmas....using the 25mm included eyepiece...although somewhat impressed with the clarity of the scope...the magnification the objects ....M42,the moon,and some random bright stars...leave a little to be desired....any advice on some eyepieces and barrows to quench my thirst for some better views???....and how much of my 280mm useful magnification is actually truly useful???...Thanks

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    Default Re: astro-engineering barlow

    Could you tell us what you are finding objectionable about the views you are getting?

    When it comes to the Moon I have a minority opinion in that I generally find it boring. At whatever magnification you use you will be seeing a bunch of craters and flat areas. I guess I do understand the challenges of identifying the various landmarks and such but I don't share much of that interest.

    Your telescope is an achromatic refractor. The reports I get indicate it is a better-than-average achromat, but being an achromat means that when viewing a relatively bright target you are going to are not going to have all of the wavelengths of light focusing at the same time and that means you are going to have chromatic aberration. If that is what you do not like about the Moon then you can get something like a minus violet (-v) filter which will effectively remove some of the unfocused light and improve the view - you may or may not find it worth the price.

    Given that the aperture of your scope is 120mm you should not plan on being able to use more than 120x most nights. If your viewing is bad you may not be able to use that much magnification.

    Given that your focal length is 1000mm your magnification with the 25mm eyepiece is: 1000mm/25mm=40x. Since you are likely to be able to use up to 120x, the shortest focal length eyepiece you will be able to use most nights will be 1000mm/120=8.3 Interestingly, that is also your focal ratio. . .

    I doubt you will use more than 120x most nights although it is possible that you will sometimes push higher than that on DSO targets. Since it is an achromat I doubt that even on a rare night with superb seeing conditions you will ever find yourself happy with a magnification of over about 180x but I could be wrong. But if we planned for 180x that would mean (just for practice) the eyepiece you would want would be 1000mm/180=5.5mm

    Personally, I'd probably stick with eyepieces in the 5-32mm range. Until you have been to a few star parties and/or have a much better idea of what you like I would probably stick with Plossl eyepieces (pretty decent and relatively inexpensive). If you wear glasses that idea might change. Because it is relatively inexpensive and decent quality I'd probably at least consider this kit: Celestron - Eyepieces - 1.25in Eyepiece and Filter Kit

    Now to give a bit of context. Reading through what I wrote one might get the idea that I am not a fan of your scope. That would be taking things too far.

    Every scope is a compromise. There is no perfect telescope no matter how many billions you may be willing to pay to buy one.

    I fully expect your scope to be a very enjoyable instrument for DSO viewing. I do not doubt that if I had it I'd be very happy with the thing. It is a surprisingly affordable refractor given its considerable size and there are a lot of targets upon which it will perform admirably well. I have an arguably much worse refractor (smaller, faster optics in an achromat) which has given me my most enjoyable view of the Andromeda Galaxy. Yup, I had both my ETX-80 and my 10" Lx200 aimed at the Andromeda Galaxy at the same time (using equivalent eyepieces) and I much preferred the view through that little ETX-80.

    You have a pretty good scope with which to explore the heavens!

    One other thing? Many of us end up not craving magnification. We might spend a night observing DSOs using a scope with the ability to usefully use 300x but may not exceed 100x for an entire night of observing. We are getting our scopes for the light-gathering properties rather than for the magnification. When we start doing planetary observations is when we want the higher magnifications and where we can usefully use those higher magnifications.

    FWIW
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    Default Re: astro-engineering barlow

    I think it is the magnification of just using the 25mm eyepiece....when I looked at Orions Nebula...it just looked like two stars with a very minimal amount of dust clouds around them..I think it's probably some of the pictures that I see on here and even though i do not expect to see as good as a lot of those...some of them are using a smaller scope than mine to accomplish such views...so i know its in there eyepieces and such...i don't know.....thought maybe going from 40x magnification to somewhere around a 100 might make me like the scope a little better...as far as chromatic aberration...i really don't have a problem with that issue yet...but the only thing i've ever really done in my life optically,is birding with a set of 10x42 lol...so very inexperienced with anything over 100 foot off of the ground...lol

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    Default Re: astro-engineering barlow

    At a guess, you are likely doing your observing in a light-polluted area and you may not have great transparency. It is also possible you aren't pointing where you really want/need to point.

    With an 80mm spotting scope with 20-60x from a moderately light-polluted backyard I can resolve the trapezium and a fair amount of nebula. It's a very good spotting scope, but it still won't outstrip what your instrument will do - so either your conditions are very unfavorable or you haven't quite got the knack of pointing and seeing.

    And seriously, we have to learn how to recognize and observe well. I once went to a star party and my wife and I were using a scope which is identical to the one being used by a first-timer. The first-timer couldn't find anything and came over to where we were. We gave him some tips and showed him a few objects and he went back to his scope and nailed everything he was looking for. He just needed to learn a little about how to see those DSOs and he was good to go!

    But in your case I'm thinking it is the conditions under which you are observing.

    If at all possible, however, you should join your local astronomy club and go to a bunch of star parties. With a good club you will find it to be the best possible learning experience.

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    Default Re: astro-engineering barlow

    I am beginning to see what you are talking about as far as seeing conditions....there is just way too much artificial light where I have been observing...I guess the only way i'll know is to find somewhere extremely dark...Do places like that still exist here...LOL

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    Default Re: astro-engineering barlow

    Dave, just to add my comments since I've had a 150mm f8 Achro refractor for quite a while, Your comment saying that the Orion Nebula looked like "two stars with minimal dust clouds" is kinda close to the truth when viewing nebula and indeed galaxy's since even Andromeda looks like a brightish fuzzy patch when viewed visually. If you like viewing DSO's then maybe search for some Globular & Open clusters since they will show some really nice detail visually.

    Also don't confuse the images posted on this forum in the astrophotoghy section with what can be seen visually, the images posted are composed of many long duration exposures that have then been processed using specialist software.

    Finally, remember that as you increase the magnification, either by using smaller eyepieces or a Barlow that the increase in magnification comes a the cost of brightness of the object.
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    Default Re: astro-engineering barlow

    Dave -

    I've had my scope, a refractor of roughly similar aperture (127mm) and focal length (952mm) to yours, only since November. I have Baader Hyperion eyepieces in 24mm, 10mm, and 8mm focal lengths, and a Celestron 2x Barlow. My eyepieces yield 39X, 95X, and 119X respectively on my scope. I've found that, so far, 119X is about as high as I'm interested in going. Using the Barlow on ANY of my eyepieces eats light to a degree I usually find unsatisfactory. With the seeing conditions I usually have, even 119x with the 8mm EP alone comes with a noticeable loss of sharpness.

    To put it another way, of the few hours I've spent with my telescope, here is the breakdown of the approximate amount of times I use each eyepiece:

    24mm..........65%
    10mm..........25%
    8mm...........10%

    That's just me. Enjoy that XLT120. From what I hear they are fine 'scopes.
    -Jay

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