1. ## Re: Collimation questions

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Further to your request in your post #1 for photos that depict the secondary collimation process, you might be well served with Parts 6, 7 and 8 of this 9-part collimation video tutorial.

Starting here

In Part 8 the presenter introduces you to the 1.25" Cheshire eyepiece/sight-tube combo tool but unfortunately does not show you the scene in its FOV. He does however give you a rather useful verbal description of how its height in the focuser can be adjusted so that its FOV gets smaller and smaller relative to the outline of the secondary.

As the annular red ring around the secondary gets thinner and thinner, the 'centering-&-rounding' of the secondary under the focuser becomes more accurate.

Cautionary warning

The presenter uses two words interchangeably. He talks about aligning the secondary under the focuser. He also talks about collimating the secondary with the primary. And he sometimes mixes these terms aligning and collimating up.

Just to be sure, in these three Parts of his entire video series, he is only addressing the positioning of the secondary under the focuser.

In the popular vernacular of this and other forums, this is commonly referred to as the 'centering-&-rounding' of the secondary under the focuser. The apparent projection of the secondary, as seen in the FOV of a collimating tool, is first centered in the FOV of the tool, and then it is rotated such that it appears to be round. This is all very cool since we know that the secondary is actually elliptical in shape.

The presenter obviously intends for his viewers to understand that he means centering-&-rounding when he uses the term align. He is aligning the secondary with the focuser, with the axis of the focuser actually.

To assist you to align the secondary with/under the focuser, he demonstrates the use of red and blue coloured cards to create contrast and to block the secondary from seeing the primary.

The fact that he does this means that he is not yet ready to align the secondary with the primary. Due to the blue plastic blocker, the primary becomes invisible to the secondary. As such, the secondary can not be aligned with the primary nor with anything on the primary. Clearly, the presenter is still talking about positioning the secondary under the focuser when he uses the words 'align the secondary'.

Next, in Part 8 after introducing the Cheshire/sight-tube combo tool, he talks about how to use its lower sight-tube portion to align the secondary under the focuser.

In Part 8 he does not talk about how to use the Cheshire/sight-tube combo tool to collimate the secondary with the primary

In that part of the process, he would have first removed the blue plastic blocker such that the secondary could see the primary and the reflections in it. He would then have ONLY used the three perimeter tilt-adjusting screws to adjust the tilt of the secondary such that it reflected the axis of the focuser directly towards the doughnut on the primary. This is what he means when he uses the words 'collimate the secondary' and more specifically, 'collimate the secondary with or to the primary'.

In the terminology used by the presenter:

When you are using a laser, the secondary is collimated with the primary when the laser spot strikes the primary in the middle of the doughnut decal.

When you are using a Cheshire/sight-tube combo tool, the secondary is collimated with the primary when the reflection of the doughnut decal is seen to be centered under/behind the blurry wire cross hairs.

A missing Part

Unfortunately, the presenter somehow quickly manages to forget, and then skips, the part where he would have shown you how to use the Cheshire/sight-tube combo tool to collimate the secondary with the primary.

He sadly jumps straight over this all important part and goes directly to collimating the primary mirror with the center of the focuser in Part 9.

That's too bad as it would have looked very cool in the video captured by his camera through the peep-hole of the Cheshire/sight-tube combo tool.

2. ## The Following User Says Thank You to PhilipLangley For This Useful Post:

michael131313 (04-06-2017)

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