alanjgreen

The 1.25 inch visual back blocks several mm (.75 inch) of the (hole diameter) light path from the SCT tube to the eye, this must have some sort of "light reduction" effect

There's no rush, the stars come around every year! Switching up to 2" is worth it as you get a wider view which is great to frame objects most notably large open clusters and large nebulas (Veil Nebula is a good example where it is simply too big to frame in a smaller EP and the extra light from the 2" can reveal more detail). But it can be expensive by the time you add in all the bits you need. You may also want to add 2" UHC filter to the list of "potential" bits & bobs.

Yes it will fit. Just means you have to leave the diagonal permanently mounted to the scope. You could always get the visual back later if you find it a pain. For example, if you want to put a filter onto the diagonal then you need to remove it from the scope to add the filter.

Simon, you need to replace the 1.25 inch visual back (supplied with the scope - the bit that screws onto the back of the scope) with a 2 inch visual back. i do not know if the visual back is removable on your scope, it can be unscrewed on the 8" version, you will have to give it a try. If it does unscrew then you also need to buy a 2" star diagonal to fit into the 2" visual back. you then need to buy some 2" eyepieces to put into the 2" diagonal. https://www.firstlightoptics.com/adapters/baader-click-lock-2-for-celestron-meade-sct.html https://www.firstlightoptics.com/diagonals/skywatcher-di-electric-star-diagonal.html You can get these items second hand to save some dough. Alan