I have a Celestron Astromaster 130EQ which came with a 10mm and 20mm lens. I can not see mars, Jupiter, or Saturn as expected, I only see white dots. What lens should I buy to view these planets.
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The 130EQ is F/5 so the 10mm lens should give a magnification of 130*5/10 = 65x. That should be enough to show Jupiter, at least, as a disk. Saturn and Mars are smaller (Mars's size varies a lot), but at Saturn's current orientation you should at least be able to make out that it has rings.
Actual details on planets are quite subtle, but if you can't at least see Jupiter as a disk (accompanied by it's 4 major satellites in varying configurations...) you probably have some issue other than magnification as a problem. Make sure your focus is correct (stars should be pinpoints) and that the telescope is properly collimated. Collimation is the alignment between the optical elements of the telescope; reflecting telescopes frequently need adjustments to their collimation; consult your manual. An improperly collimated telescope won't show images properly.
When you have focus and collimation down, you can address magnification. Higher magnification can help you see detail, but viewing features of planets is usually more limited by atmospheric conditions and the design of the telescope rather than simply magnification. The maximum useful magnification of your telescope is 150-200x. A 4mm eyepiece will get you there. A Barlow lens can be useful, increasing the magnification of your eyepieces by 2-3x, but doesn't always work well with short focal length reflectors like yours.
