Using a Cheshire

[cyborg421]

I have borrowed a Cheshire form FLO and have read about collimation but am still unsure. I suppose 2 things are most noticeable when I look down the Cheshire.

1) The black dot in the centre

2) The cross hairs of the Cheshire but also those of the supports at the top of the scope (Skywatcher 10" DOB). I can't see the circle in the centre of the primary and don't really know if I should be adjusting the primary or secondary.

Help!

Simon

[sixela]

If this is at night: yes, you also have to illuminate the centre spot in order to see it.

By the way, what you have is strictly speaking a combination tool (sight tube and Cheshire).

For now, I'll assume yo udon't want to mess with secondary placement/rotation yet (it's the hardest aspect of collimation but also the least important, unless things are really bad).

The second step is to use the secondary's tilt screws to adjust the tilt so that the focuser axis points to the middle of the primary. The visual cue is that the primary's centre spot is then behind the cross hairs (by the way, the spider vanes should always be ignored).

The third step is to use the primary's collimation bolts to adjust the tilt of the primary so that the centre spot reflection is concentric with the bright Cheshire ring reflection.

How you illuminate the Cheshire ring and the centre spot depends on the exact model. If it's one with a cutout in the side, you illuminate the Cheshire ring from that side (at night, with a LED lamp) and illuminate the centre spot on the primary through the front (usually with a clip-on LED lamp by night). It's a lot easier to do in daylight (just point the scope to the sky --not the sun!-- and the cutout in the combination tool to the dky as well.

[Chris H]

Read Astro Baby's guide to collimation

Astro Babys Guide to Collimation

After that everything should become clear.

[jwallis]

Just read Astros article, and this has really made things clear.

[HappySachs]

Read Astro Baby's guide to collimation

Astro Babys Guide to Collimation

After that everything should become clear.

Thanks for the link (and a big thanks to Astro Baby)

[jwallis]

I have just done my first collimation on my new scope, and thanks to Astro babys easy guide, i have got it near on. Or as well as i can .Thank you for the easy explanation.