Farpoint Primary Mirror Center Marking Kit LARGE — 12" to 26"

Product Overview

The Farpoint Primary Mirror Center Marking Kit LARGE marks the exact centre of a big Newtonian or Dobsonian primary — mirrors from 12" to 26" in diameter. It contains a large precision-cut acetate template scaled for those apertures, together with eight triangle-shaped centre-mark targets.

The centre mark is what every collimation tool references. A laser reads where its beam returns relative to it, a Cheshire lines up reflected apertures around it, and an autocollimator stacks reflections of it. The triangle targets are cut so their edges meet the outside of the illuminated field seen through a Cheshire, which turns a judgement about centring into a straightforward read.

Who It's For

This is a good match if you own a large Dobsonian or Newtonian — a 12" to 26" solid-tube, truss or collapsible scope — with an unmarked primary, a mark that has lifted or faded, or a mirror that has just come back from recoating. It is equally the kit for a mirror maker finishing a large primary, and for anyone assembling a truss Dob from components.

Key Features & Design

• Large precision-cut acetate template: scaled for primary mirrors from 12" to 26", so the centre is located geometrically rather than measured across a large, awkward surface.
• Eight triangle centre-mark targets: enough for the job, a second attempt, and spares.
• Triangular geometry: the edges meet the outside of the illuminated field through a Cheshire, which makes the alignment readable instead of estimated.
• Universal reference: works with laser collimators, Cheshire eyepieces and autocollimators of any make.
• One-time job: the mark stays put until the mirror is next recoated.

Why Centring Accuracy Scales With Aperture

Collimation brings the optical axes of the primary, the secondary and the focuser into agreement, and every tool that does it compares something against the centre of the primary. Without a mark there is no reference at all — the tools still show you a picture, but there is nothing in it to align to.

On a large mirror the accuracy of that mark matters more, not less. Big primaries generally come with fast focal ratios, and a fast Newtonian has a tighter tolerance for primary tilt than a slow one, so a given placement error translates into a larger optical consequence. The error is also self-concealing: because the laser, the Cheshire and the autocollimator all reference the same mark, an off-centre spot biases every adjustment by the same amount and none of the tools will contradict it. That is why the kit uses a cut template scaled to the aperture rather than leaving you to find the centre of a 20" disc with a ruler.

Recommended Uses

• Marking a large unmarked primary: including mirrors bought separately or supplied unmarked with a truss kit.
• After a recoat: recoating removes the old mark, and the mirror needs a new one before it can be collimated.
• Replacing a lifted or inaccurate mark: worth redoing on a big mirror, where the consequences scale.
• Truss and collapsible Dob assembly: the reference point for the alignment routine you will use every night out.
• ATM and mirror-making projects: a finished large primary needs marking before first light.

Compatibility and Accessory Notes

• Mirror size: Newtonian and Dobsonian primary mirrors from 12" to 26" in diameter.
• Smaller mirrors: up to 12.5", the standard Farpoint Primary Mirror Center Marking Kit is the correct template, and we stock it. The two overlap between 12" and 12.5".
• Telescope types: reflectors only. SCTs, Maksutovs, refractors and other catadioptric designs do not use a primary centre mark.
• Works with: Farpoint laser collimators, Cheshire eyepieces and autocollimators, and collimation tools of any other make.
• Not the template supplied with Farpoint kits: Farpoint's lasers and collimation kits include the standard template for mirrors up to 12.5". If your mirror is larger, this is the one you need.

Good to Know Before You Order

• Check your mirror diameter. This template covers 12" to 26". Below 12", the standard kit is the right size and we carry it.
• Reflectors only. A primary centre mark is a Newtonian and Dobsonian technique — SCTs, Maksutovs and refractors collimate differently. Tell us what you have and we will point you at the right approach.
• It marks the mirror; it does not collimate it. The mark is the reference a laser, Cheshire or autocollimator then aligns to, so it is the first purchase rather than the only one.
• A large primary is heavy and awkward to handle. Marking means removing it from the mirror cell, so it is worth clearing a large padded surface and, on the biggest apertures, having a second pair of hands.
• Take your time on placement. Eight targets are supplied precisely because the first attempt does not have to be the final one.

Frequently Asked Questions

Is it difficult to set up?

The marking itself is simple — the template locates the centre and a triangle target goes on it. What takes care on a large scope is the handling: the primary comes out of its cell, and a 16" or 20" mirror wants a cleared, padded surface and an unhurried hour. Eight targets are supplied so a first attempt you are not satisfied with costs nothing, and Farpoint publishes preparation guides and downloadable collimation references if you would like to read the sequence through beforehand.

Why does the centre mark matter so much on a big mirror?

Large primaries usually come with fast focal ratios, and a fast Newtonian has a tighter tolerance for primary tilt. A placement error therefore has a larger optical consequence — and because every tool references the same mark, the error stays consistent and invisible rather than showing up as a disagreement between tools.

Why triangles rather than a round dot?

A triangle gives you edges to read against. The edges meet the outside of the illuminated field through a Cheshire, so you match straight lines to a boundary rather than judging whether one circle sits centred inside another.

What size mirrors does this fit?

Primary mirrors from 12" to 26" in diameter. Under 12", the standard Farpoint center-marking kit is the correct template.

Does the mark affect the view?

No. The centre of the primary sits in the shadow of the secondary mirror, so that area contributes nothing to the image either way.

Is this the template that comes with Farpoint's collimation kits?

No — those include the standard template for mirrors up to 12.5". This LARGE version is the separate purchase for bigger apertures.

Bottom Line

In short: a large precision-cut acetate template and eight triangle centre-mark targets for Newtonian and Dobsonian primaries from 12" to 26". It gives every other collimation tool a reference to work from, and on a big fast mirror it is the step the rest of the alignment rests on.