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A 100 mm / 4 in. is really the minimum for good planetary observations. I used a Orion 100 ED for several years. The images esp. on the brighter planets was very satisfactory. Subtle details could be seen on Jupiter and Saturn under steady seeing conditions. Maximum magnifications of 200x - 240x could be used - more then that and the image dimmed. A good 4. in will give you many years of rewarding viewing. I did go up to a S.W Equinox 120 ED about a year ago - mainly as I got great trade in deal. Yes the 120ED certainly gives you a brighter image, more detail and can go to 300x on steady nights. It gives you more 'headroom' to play with. Having said that I still would be happy to use my 'old' 100 ED.
Chris
Last edited by chris lewis; 30-04-2010 at 10:48 AM.
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