Just a note here. This telescope is a very compromised design and it has a lot of behavioral quirks.
This scope looks small for a 10" and one of there reasons for that is that it is f/4.7, vs f/4.9 or f/5 for many other scopes, but also it uses what would be considered an unconventional tube sizing. Rather than have maybe a more traditional 12" tube, the tube here is only slightly larger than 11".
Now there is a consequence here, and it is one that planetary observer's and people that use binoviewers to do planetary observing should be aware of if the goal is to get the best possible planetary performance.
Because the scope uses a small tube diameter, this means that the focuser tube can very easily project into the light path. In fact, this projection can be quite deep.
This picture shows the extent of intrusion when the focuser is racked all the way in and this configuration should be avoided at all costs for planetary observing because as can be seen, the area of the obstruction is quite large and probably combined with the secondary mirror, brings the total obstruction to probably 35% or 40%.
Even when racked only half way out, the intrusion is still considerable. This focuser has a travel range of 1.5" and at 3/4th inch, there is still considerable intrusion bringing the obstruction to probably 30%
To be completely free of intrusion, the focuser has to be raked out 1.25".
Now the quirk here is that many eyepieces won't reach focus without the extensions but the extensions are so long that the will force the focuser to be racked in considerably.
For this reason, when doing planetary observing, my recommendation would be to avoid extensions and instead try to use a configuration that requires the most outward travel of the focuser tube. This can be done buy using 2" extensions on the eyepiece of on the 2" to 1.25" adapter (if using 1.26" eyepieces). Rack the focuser all the way out, then draw or slip focus the extended eyepiece as necessary to get the correct rough focus, and then you have .25" of fine focus to play with.
Now this only matters if it matters to you. I have been doing planetary observing for going on 40 years now and my experience is that while no one small thing by itself will usually be an issue, small things do add up, but in this case, if you are using an extension that requires considerable inward focuser travel to reach focus when planetary viewing, the obstruction becomes abnormally high and does lower contrast. I can see the extra diffraction at the eyepiece.
When properly set up (Get rid of three of the mirror retention plates and reduce the size of the remaining ones) this telescope gives quite excellent planetary performance, but using it with the extensions as shipped by Sky-Watcher and having excessive inward focus travel (anything more than half an inch) and you are in SCT land for contrast, and worse if you are running with the focuser nearly all the way in.
It is not the best design. This scope should have one of the low profile Hybrid focusers as an option. The standard focuser is ill suited to the design.
And apologies for the poor images. I did not want to invest more time than essential here to make the point, and while the quality is poor, they are clearly sufficient to show the issue.
Edited by Eddgie, 19 October 2020 - 10:42 AM.