Celestron C8 vs Edge HD 8 for visual ?

[Merlin66]

For spectroscopy the challenge is to focus the target star and maintain the target image on a 20 micron slit gap for at least 10 min subs.

All I can say is that there are many amateur spectroscopists around the work who regularly use C11 (or C14) SCT's for successful long duration exposures (up to two-three hours) with no significant focus shift problems.

What more can I say?

[nightfisher]

31 minutes ago, Peter Drew said:

Yes it does. Best to move the mirror upwards against gravity before collimating and then always focus from the same direction. 

This is what i have always tried to do with maksutov scopes, try to find the sweet spot  pushing the mirror back up the tube as it were

[Stu]

2 hours ago, Merlin66 said:

For spectroscopy the challenge is to focus the target star and maintain the target image on a 20 micron slit gap for at least 10 min subs.

All I can say is that there are many amateur spectroscopists around the work who regularly use C11 (or C14) SCT's for successful long duration exposures (up to two-three hours) with no significant focus shift problems.

What more can I say?

I guess once focused, the mirror should not move unless the scope tips the other way during tracking?