Hallo André,
wenn man zu einem Zeitpunkt beobachtet, wo Mars nah an der Erde (Opposition) und die Marsmonde möglichst weit links oder rechts vom Mars sind (hohe Elongation) und man außerdem das Teleskop so verschiebt, dass Mars gerade nicht mehr zu sehen ist, dann soll für einen geübten Beobachter unter besten Konditionen bereits ein 4-Zoll-Teleskop ausreichen. Mit einem 10-Zöller sollte jeder wenigstens einen Mond sehen können.
http://www.observing.skyhound.…allow_sky/mars_moons.html
"Spotting both moons in an 18-inch or larger telescope is a bit of a challenge, but once you do they are easily seen on a good night. I found Phobos to be the easiest, despite it's proximity to Mars. I estimate that a very dedicated experienced observer from a good location should be able to spot at least one moon in a 10-inch. Even an 8-inch should not be out of the question. I probably spotted Deimos in my 6-inch f/8 Newt. during the excellent opposition of 2003. I say probably because I was not able to be absolutely certain. Any observation in smaller apertures is going to be marginal. At best you will glimpse a faint speck at the proper position then it will disappear. If this happens be patient. It may reappear again. The more times you spot it the more certain you will be of your observation. And you may just get lucky enough to see it for several seconds--long enough to be pretty darned sure. But there are a lot of stars out there. Be sure that you have eliminated the possibility of a field star near Mars. Could it be done in a 4-inch? I really think it might be possible with the right observer under just the right conditions. Doing so would be a real feat!"
Gruß, Günther.
