On May, 16th with my astro amateur friend we spent a few hours on Jupiter observing from my backyard. We used 130/910 Photoline triplet, 120/600 Skywatcher achromatic refractor and Celestron SCT8″. There were also some eyepieces around: ES 16mm 82 degree, ES 6.7mm 82 degree, Ethos 13mm, Antares ortho 6mm and TV x2 barlow. Seeing was decent.
Jupiter presented itself quite good with 130/910 APO triplet and ES 16mm eyepiece and barlow. There was a dark area in the upper equatorial belt that we thought to be GRS, but it turned out that is another smaller structure visible in the amateur images (images in the post were made one day later, so this dark speck is not visible). Upper polar belt was sometimes visible as split to double. Unfortunately we found out, that ES 16mm 68 degree eyepiece is pretty sensitive to viewing angle, even small deviations from perfect eye position effected in chromatic aberrations visible at the Jupiter edge. So we replaced this one with Ethos 13mm (still with barlow) and the problem disappeared. Jupiter now was visible almost flawless with the quality spoiled only be seeing. ES 6.7mm 82 degree eyepiece (without barlow) gave similar quality Jupiter image plus there was no visible chromatic abberations even with non axial viewing. We tried also to add barlow (300x magnification) but then image contrast was lost and no more details were visible. Last eyepiece we tested was 6mm Antares ortho. Detail level was the same like for Ethos 13mm with barlow or ES 6.7, but contrast seemed to be better and overall impression was also more pleasing.
One can easily guess that 120/600 achromatic refractor is not a perfect instrument for planetary viewing – and that is true. With ES 6.7 eyepiece equatorial belts were visible, and also this dark structure in the upper belt for some momets could be spotted. But overall detail level was much lower, and also there was huge violet halo visible around the planet. This halo could not be eliminated with Fringe Killer filter.
This night winner was Celestron SCT 8″. Compared to 130mm triplet Jupiter image was little bit more detailed, and most fain structures (like small flocks in the equatorial belts) were defined better. Also upper polar belt was split to double for almost all the observing time. We used 13mm Ethos only, it would be good to have some 9-10mm eyepiece, because conditions were good enough, but definitely not good enough for 6-7mm eyepiece we had these night. SCT image contrast was also very good, maybe not as good as with 130mm refractor, but larger SCT aperture allowed for convenient observations.