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. The ETX-90 comes with a 26mm Super plossl eyepiece. Rather than just get the most powerful eyepiece available, I'd suggest stepping up slowly. The next eyepiece to look for would be a 15mm, and then a 5 or 6mm for high magnification. Just the three eyepieces should let you do about anything you would need with that scope. Please let us know if there is anything else we can do for you.