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  1. #1
    cpsmith1020's Avatar
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    Default Lack of Details on Planets Through Telescope? What to Do? Buy?



    I recently purchased an Astromaster 130 EQ. It came with two eyepieces, a 20 mm and a 10mm. I would like to get good details on the visible planets first, and then work my way to deep sky viewing. I've looked at both Mars and Jupiter, but with either ep, I'm not getting much more than what I see with the naked eye (just a little larger). Is this what I should expect with these ep's and I need something stronger, or is it the alignment in the mirrors?
    Last edited by admin; 04-17-2012 at 12:15 AM. Reason: descriptive title please

  2. #2
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    You're going to have to re-learn how to "see". It sounds silly, but it's true. Consider this:

    • The full moon, when viewed with the naked eye, is 1/2 degree (or 30 arcminutes, or 1800 arcseconds) in diameter.
    • Mars, right now, is 12 arcseconds in diameter
    • 1800 / 12 = 150x power to make Mars have the same apparent diameter as the full Moon appears with the naked eye.


    With your 10mm eyepiece you're getting 650/10 = 65x power, which makes Mars appear 12*65=780 arcseconds wide (a little under half the diameter of the naked-eye full moon). This should be plenty to see the disc of Mars and even see a little detail.

    BUT...you have to learn to see it. Since the beam of light coming out of the scope (exit pupil) is only 2mm in diameter (with the 10mm eyepiece), and Mars is a tiny dot of light inside that beam, your eyes will trick you into thinking that it's this tiny speck. But it's not! Spend some time at the eyepiece and really concentrate on that tiny speck. Try to ignore the surrounding area in the field of view. You'll find that as you practice, you'll be able to fight off your brain's natural reaction to assume that what you're looking at is a tiny featureless dot, and you'll start to see detail you were missing before.

    A moon filter may help to cut the glare some and draw out more detail.

    If you have particularly good seeing conditions (steady air), you can add a 2x Barlow lens and get 130x power out of your scope (1mm exit pupil) -- this is the maximum I would recommend trying to use with your scope.

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  4. #3
    goldken51's Avatar
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    Default

    I'm Pretty new to this too, but you could purchase a 2x Barlow and that would double your magnification. I bought a3x and no matter which eyepiece I use everything is still just a little bit bigger and fuzzier with it. Mine is a Meade #128 1.25" 3x Telenegative. I'm wondering if my telescope needs to be collimated.
    Ken

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    Mars is really small so its hard to make out any detail usually with that size scope ( I have the exact same size scope). With Jupiter you should be able to make out the cloud bands and see the 4 largest moons. Jupiter is also low in the sky now and not ideal to observe. Try Saturn with the 10mm you'll be in for a treat!
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    Default

    Quote Originally Posted by goldken51 View Post
    I'm Pretty new to this too, but you could purchase a 2x Barlow and that would double your magnification. I bought a3x and no matter which eyepiece I use everything is still just a little bit bigger and fuzzier with it. Mine is a Meade #128 1.25" 3x Telenegative. I'm wondering if my telescope needs to be collimated.
    Magnification isn't free. There are fundamental limits to both the optical components and your retina's resolution.

    As you increase magnification, the exit pupil gets smaller and smaller. After the exit pupil shrinks below 1mm (eyepiece length == focal ratio), the image starts to get noticeably dimmer, and you begin reaching the limits of the mirrors and lenses in the system. When the exit pupil gets to .5mm (eyepiece length == 1/2 focal ratio) you've reached the reasonable limit of what the human eye can perceive clearly, not to mention the limits of what your scope can actually handle.

    So just because you *can* add a 2x or 3x barlow to the scope, doesn't mean that doing so will actually help you see things any bigger or more clearly.

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    I concur, last night Saturn looked better with the 6.5mm without the 2x Barlow. With it, it became impossible to get good focus.

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    So this scope can't get anywhere near it's suggested max power of 260x, I only had it up to 78x and noticed it getting fuzzy. At 195x Venus was a little larger, and I could see it was crescent shaped. At 78x I could just make out the crescent shape.

    Oh well. Thanks for the info!
    Ken

    130mm x 650mm Bushnell Truss Dob.

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    Default Better Saturn View

    Well Saturday night I had a chance to let my scope cool down longer than anytime before. I also wanted to test the views with my new Meade 3x Barlow lens. I started with the 25mm and went gradually up to my 9mm with it, and saw an amazing sight of Saturn. I was able to see the rings, but just as one big white ring, but I could see the planet itself seperated by a pretty good black space between it and the rings. I wished I could see a little color seperation in the view, But I guess I will just have to wait till I can afford to get maybe a 10 or 12 inch scope some day down the road.

    Clar skies all!
    Ken

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    Default

    Quote Originally Posted by goldken51 View Post
    So this scope can't get anywhere near it's suggested max power of 260x
    It can probably do 260x, but only in perfect seeing conditions. Most of the time, 130x will be its limit.

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    goldken51,

    I was able to see full detail and coloration of Saturn last night with a 102mm refractor at 160x. The #1 thing that I've noticed that affects Saturn's image in the eyepiece is the seeing conditions. As soon as the air gets turbulent, all of the detail washes away and it looks like a white circle with a white ring around it. When the air calms, the colors start to come out.

    The #2 thing I've noticed is that a quality eyepiece makes a big difference. If you're using the eyepieces that came with your dob, chances are you will see a lot more of Saturn with a 5mm premium eyepiece with high quality coatings and good spherical correction. Since you're using a manual dob, you'll want a reasonably wide field so you don't have to keep bumping the scope at high magnification. Something like the 4.5 or 6.5mm Meade Series 5000 HD-60 ($79), the 4.7mm Explore Scientific 82 degree ($120), or a 5mm Baader Hyperion ($140) will all work great in your scope. They all have good spherical correction and high quality coatings to reduce color-robbing glare.

    Finally, always make sure your scope is well collimated with a successful star test before observing Saturn. You'll be shocked at the difference, even with a low-end eyepiece, that a well collimated scope makes!

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