Telescope Eyepiece, 32mm, 2" dia

This project was inspired by Jerry Oltion's article in the September 2020 issue of Sky & Telescope, p. 74.

This is an eyepiece for an astronomical telescope made from lens sets available from Surplus Shed (surplusshed.com). This is based on the following item:

L3715 Erfle, 32mm fl

This set consists three lenses (eye, middle, field) approximately 25mm to 26mm in diameter.

This is a remix of the 32mm Erfle for a 2" focuser. The original is here: https://www.thingiverse.com/thing:4597001

IMPORTANT: I haven't printed this specific eyepiece. I've remixed four other eyepieces for a 2" focuser and all printed with no problems. ALSO, the dimensions (diameter, thickness) of the lenses in the Surplus Shed lens sets are not 100% consistent. You may find that the lenses don't fit well into the lens spacers.

The eyepiece consists of the following parts:

1) 2" barrel with a 1.5mm pitch external thread,
2) Housing with a matching internal thread,
3) Three lens spacers, one each for the eye lens, middle lens, and field lens.
4) Flexible eye guard.

I made these from ABS except for the flexible eye guards. ABS is more durable, lighter, and has a less glossy finish than PLA. The eye guards are printed from black TPU

The vertical resolution of the print is important to get acceptable quality on the threads. I printed mine at 0.12mm vertical resolution and a speed of 20mm/s. You can print all the parts without supports, but some files need to be flipped 180º when slicing.

I have compared these eyepieces with commercial eyepieces from Meade. The 3D printed eyepieces compare very favorably. There's a little distortion at the edges, and some chromatic aberration. A view of the moon shows color fringes on some of these designs, whereas the Meade eyepieces are color-free. The FOV of the 7mm eyepiece is very narrow. Contrast is as good or better than the Meade lenses, and I notice no internal reflections.

Print Settings
Printer brand:
Anet

Printer:
A8

Rafts:
No
Supports:
No
Resolution:
0.12mm

Infill:
20%

Filament brand:
Inland

Filament color:
Black

Filament material:
ABS & TPU

Notes:
Make all parts from ABS except for the flexible eye guards, which are TPU. Take care in assembling the lenses; they must be properly oriented and in the correct order. Surplus Shed provides an info sheet with the lenses, but doesn't give a lot of specifics about possible designs. They specify that the lenses "should be as close as possible without actually touching." My design has a nominal spacing of 0.48mm, which seems to work well. The clearance between the lenses and the spacers is 0.3mm. This seems to work well to keep the lenses in place but allows them to slip easily into the spacers. The vertical resolution of the print is important to get acceptable quality on the threads. I printed mine at 0.12mm vertical resolution and a speed of 20mm/s. You can print all the parts without supports, but both housings (internal & external threads) need to be flipped 180º when slicing.