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Rima Messier and two eyepieces

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Posted (edited)

The Meteoblue forecast had promised good seeing conditions, and the terminator was close to the Messier double impact crater this morning, so I tried once again to spot the elusive rille Rima Messier, that I've observed only twice up to now. The 18" Obsession was at ambient temperature at 02.30 CEST; the seeing was variable, mostly Antoniadi 2 - 3, and, with a 10 mm Ortho, giving 205x mag, I could make out the Messier craters, the double "tail", and the small craters Secchi A and X, quite distinct. The rille itself, 100 km long, starts from Messier A and extends NW between the Secchis, touching a smaller, unnamed craterlet S of them (all three shown in the picture below). For 10 mins, the rille remained invisible; with improving seeing conditions, I was able to make out repeatedly for 2 or 3 seconds it's fine, sharp, rather straight line to almost it's full extent. Switching to a 6 mmf Ortho gave only a little improvement. The Rimae Secchi, N of it and at right angles, were, in contrast, visible more easily and appearing as rather "broad" lines. Just for fun, I switched to the trusted Seben 8-24 mmf zoom eyepiece, and was very surprised, as it delivered an almost equal view - very sharp, clear, without reflections. I compared it at the 10 mmf setting to the top notch 10 mmf Zeiss ortho, and found very little difference between them; just a little loss of brightness, and the sharp views of the Rima Messiers appeared to be a tad shorter in duration. Very astonishing for a 60€ eyepiece, that's not laid out for a f/4.5 aperture ratio. - The gibbous Mars showed it's already smaller ice cap, and a few darker shades; my usual disappointment with my nemesis. But very pleased having spotted the Rima for the third time, and so to bed at 03.45.

Attached a picture (from the net):


Thanks for reading


Edited by Nyctimene
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Nice report Stephan :icon_biggrin:

These lowish cost zooms can be rather good !

My 7.2-21.5mm zoom plus the Baader 2.25x barlow lens is more often than not my first choice with my refractors and often the only things I use. I've a case full of Tele Vue and Pentax eyepieces doing very little just now :dontknow:

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