Collimation cap

[David Scott]

Hi,

I've a Celestron 10 inch Dob which I've been trying to collimate using the collimation cap that was included. I've looked at a lot of stuff online and by and large I think I kind of understand it, but I have a question. It seems fairly fundamental and  I thought I saw it answered somewhere but I haven't been able to find it again.

 

The collimation cap is lined with reflective foil of course, except for the hole you look through which shows up as a dark spot when you look through it.

When the scope is collimated should this dark spot be at the centre of the doughnut on the primary?

Thanks.

[Spile]

Yes it should as per the following:

[David Scott]

Thank you. If the dot is exactly in the middle of the doughnut but the cross made by the vanes doesn't quite match up exactly (which seems to be the case) is it because the secondary is slightly misaligned?

 

[Spile]

22 hours ago, David Scott said:

Thank you. If the dot is exactly in the middle of the doughnut but the cross made by the vanes doesn't quite match up exactly (which seems to be the case) is it because the secondary is slightly misaligned?

 

 No. Ignore the vanes. The important thing is that the donut and centre of the bright ring are concentric.

Also note that the dark secondary reflection “points” towards the primary…

Edited June 5, 2023 by Spile

[David Scott]

Thank you.