Telescope Reviews: A well tuned C8 on Jupiter

Last night, I treated the 5" refractor (Meade AR5) to some Jovial viewing

. Whilst not a view for view comparison to the C8 on one night, I believe I am able to offer some interesting points of comparison. Most observations below were made at ~170x

1) Overall brightness - obviously less in the 5", though the C8 is almost verging on too bright for comfort, and I may experiment with a ND filter.

2) Overall presentation: the 5" has some color from chromatic aberration. This is to be expected. There is also some spherical aberration (mild under-correction according to crude star testing). Both these factors give the scope a unique character in image presentation and perhaps a reduction in contrast and difference in colour rendition compared to the C8. That said, during steady moments, some finer structure was glimpsed in the atmospheric belts. The C8 would definitely reach well beyond in terms of detail when seeing allows.

3) Settling time - this was interesting: Conditions were cool, but above freezing, outside temp ~50F and falling. At first I ascribed the unremarkable views to poor seeing, as detail on the Jovian disc seemed to come and go, disrupted in bouts of "high frequency" disturbance. Even during settled moments, however, there seemed to be a soft character to the images with focusing seemingly indeterminate.

BUT, as the glass and tube acclimated over the course of ~30min the view transformed. Focus became sharp & easily found, with the initial softness in the image greatly abated. It also seemed that in the later stages of cooling the purple fringing from CA was much reduced. Quite a transformation! At this point a shadow transit had just begun, and a well defined dark (purple-ish) pin-point shadow appeared on the disc of Jupiter whilst a small pin-point of light hovered just outside.

The fun part for this observer is enjoying the presentation made by any intrument. The 5" and the C8 each have a place in my affections. It was interesting that cooling of the refractor was more an issue than I had anticipated. Yes, it is the instrument of choice if I'm not able to plan ahead, yet not ready to go at full power straight out of the starting block. This offsets a little of the issues one might raise to the C8, or even the 5" Mak. Seeing conditions are the major factor at my location which determine visible detail - often the 5" will show all there is to be seen. On the plus side, it is very resistant to condensation - making it a great (safe) choice on dewy nights.

Ed