I Asked Copilot How to Make a Mount for 52mm Achromatic Lens

Mirror mounts are obvious.  I have done them before.  It gave me a very detailed explanation for making it out of PVC with drawings.

🛠 Materials

• 52 mm achromatic doublet lens (crown + flint, already matched)
• PVC pipe with inner diameter slightly larger than 52 mm (commonly 2" schedule 40 works well)
• PVC coupler or end cap (for rear support)
• Thin brass or plastic shims/spacers (0.1–0.2 mm thick)
• Retaining ring (can be cut from PVC or aluminum stock)
• Black matte paint (for internal surfaces)
• Small screws (optional, for collimation adjustments)

⚙️ Step‑by‑Step Build

1. Prepare the PVC tube
• Cut a section of PVC pipe ~60–70 mm long.
• Bore the inner diameter on your lathe to a snug fit for the 52 mm lens.
• Leave ~2 mm clearance so the lens can drop in without binding.
2. Machine the lens seat
• Face one end of the tube flat.
• Cut a shallow internal shoulder (~2 mm deep) so the front crown lens rests squarely.
• Ensure the seat is concentric with the tube axis.
3. Insert the crown lens
• Place the convex crown element facing outward.
• Add three tiny foil or plastic spacers evenly spaced around the edge to maintain the air gap.
4. Add the flint lens
• Place the concave flint element behind the crown, aligned with the spacers.
• Check that the doublet sits flush and centered.
5. Secure with retaining ring
• Turn a PVC or aluminum ring on your lathe to thread or press into the tube.
• The ring should hold the lens gently — not tight enough to pinch.
• If threading PVC is tricky, you can cut a groove and use a snap‑in ring.
6. Blacken the interior
• Paint the inside of the cell with matte black to reduce reflections.
• Also blacken the lens edges if not already done.
7. Rear support / mounting
• Attach a PVC coupler or end cap to the back of the cell.
• Bore it to fit your telescope tube.
• Optionally add three push‑pull screws around the perimeter for collimation.
8. Final assembly
• Test fit the cell into your telescope tube.
• Adjust screws (if used) to align the optical axis.
• Verify that the lens is secure but free to expand slightly with temperature.

📐 Simplified Cross‑Section Drawing (textual)

Code

   Front (sky side)

   -----------------

   | Retaining Ring |

   -----------------

   | Crown Lens     |

   | Spacer Foils   |

   | Flint Lens     |

   -----------------

   | Rear Support   |

   -----------------

Telescope Tube Connection

This diagram shows:

• Retaining ring: Holds the crown lens from the front
• Crown lens: Convex side facing outward
• Spacer foils: Maintain air gap between crown and flint
• Flint lens: Concave side facing inward
• Rear support ring: Secures the lens stack from behind
• PVC tube body: Main housing, lathe-bored for precision
• Telescope tube interface

Machining Tolerances & Dimensions

🔹 PVC Tube Body

• Inner diameter (ID): 52.2 mm ± 0.1 mm
• Slight clearance for the lens stack (52.0 mm nominal lens diameter)
• Shoulder depth: 2.0 mm ± 0.1 mm
• For seating the crown lens
• Tube length: 60–70 mm
• Allows space for lens stack + retaining ring

🔹 Crown Lens Seat

• Seat diameter: 52.0 mm ± 0.05 mm
• Snug fit without binding
• Flatness: ≤ 0.05 mm deviation
• Ensures optical alignment

🔹 Spacer Foils

• Thickness: 0.1–0.2 mm
• Use 3 evenly spaced shims
• Material: Brass, Mylar, or thin plastic

🔹 Flint Lens Fit

• Same diameter: 52.0 mm ± 0.05 mm
• Should rest flush against spacers

🔹 Retaining Ring

• Outer diameter: Match PVC ID (52.2 mm)
• Thickness: 2–3 mm
• Fit type:
• Press-fit: OD = 52.3 mm ± 0.05 mm
• Threaded: Cut internal threads in PVC, external threads on ring

🔹 Rear Support Ring

• Outer diameter: Match telescope tube ID
• Mounting method:
• Press-fit or screw-on
• Optional: 3 push-pull collimation screws (M3 or M4)

🌡 Thermal Expansion Allowance

• PVC expands ~0.07 mm per 10 °C per 100 mm
• Leave ~0.2 mm axial clearance to avoid lens stress
• Avoid tight radial clamping — use gentle retaining pressure

🎨 Surface Treatment

• Blacken interior: Use matte black paint or flocking
• Edge blackening: Paint lens edges to reduce stray light
•