Quick question on collimating a Dob.

[White Rabbit]

Hi guys/gals.

What is the best position to collimate in? Horizontal or vertical?

Thanks

[rmcpb]

To be the absolute best you can get you would actually calculate the angle you would be observing at then collimate it at that angle.

For the rest of us about 45 degrees works :)

[Starkler]

Whatever is most comfortable for you.

If your collimation changes with altitude, then you have an issue to be sorted first.

[Geoff45]

I would suggest 45deg or more, just to make sure the mirror's weight causes it to seat properly when you adjust, but really if the scope is properly constructed, any position should work.

[erick]

If you are using a laser that you can observe from the primary mirror end, watch the location of the return spot as you swing the OTA from horizon to zenith. Bet you it moves on these mass produced ones. It moves about a mm on my 12" GSO dob. I collimate at around 50-60 deg elevation.

ps. it's worth cranking the focusser all the way in and out and watching that return spot (and the spot location on primary mirror as well). Big movement means issues to be sorted, as Geoff says.