Removing the Centre Spot

[Hans Tucker]

Any trick to removing the centre spot on a Newtonian Primary Mirror? The mirror has a circular centre spot and I need to affix a red triangle.

[Rainmaker]

Wet a cotton bud with isopropyl alcohol and use it to dampen the spot, leave for a few minutes and then use a toothpick to prise it off the mirror.....

[glend]

I have to ask, do red triangles have some sort of magical qualities that a white circle lacks?

[Hans Tucker]

Was wondering the same thing. I came across these alternative centre spots when researching the Catseye Collimation Tools and I thought they were introduced to make using the Autocollimator easier. Farpoint have introduced their own Autocollimator and have supplied red triangles with their spotting template.

[Rainmaker]

Yes Glen, they have corners, which make it possible to identify the four separate reflections when using an autocollimator........ two face left, the other two reflections face right so you can identify them when collimating.....

https://www.catseyecollimation.com/acexplain.html

[sharpiel]

It’s under the secondary shadow so use anything sharp, like a razor or knife point to lift an edge then tweezers to remove.

[ChrisV]

I couldn't remove the circle on my GSO newt. So just stuck the triangle over it. It's fine with the cats eye collimator

[Jason D]

Autocollimators create flipped reflections of the center spot that needs to be precisely stacked. A triangle will make the task easier as opposed to a ring shape. Catseye Hotspot works even better. See all 3 shapes in the attachment.
Jason

[RyanJones]

If your GSO is like mine, the center spot isn’t stuck on. The mirror coating is missing. Shine a light from the rear of the cell and you’ll see the doughnut light up.

Cheers

Ryan