DIY accessories

Phone holder for the telescope

Zenigo finds where your telescope points by photographing the sky with the phone camera. That works best when the phone sits on the telescope firmly and always in the same place. Here is how to build such a holder yourself from a few standard parts and one 3D-printed adapter, which you can adjust to your telescope and download right here.

Why a rail in the finder shoe

A phone strapped to the tube with a bike or tripod clamp works, but it shifts a little whenever you push the telescope, and after every setup it sits somewhere else. Each time, the eyepiece point no longer fits and has to be set again.

Almost every telescope already has a precise, sturdy mount for small accessories: the finder shoe. A printed adapter slides into it like a finder and carries a Picatinny rail, the rail system known from riflescopes and camera rigs. A camera mount clamps onto the rail, and the phone holder screws onto its 1/4" camera thread:

• Rigid: the shoe and the rail clamp with screws, nothing wobbles when you move the telescope.
• Repeatable: the rail has a slot every 10 mm. The holder goes back into the same place, so the eyepiece point stays valid from night to night.
• Quick: the adapter slides out of the shoe with the phone holder still on it. Nothing to strap or tape to the tube.
• Expandable: the rail takes anything with a Picatinny clamp or a 1/4" camera thread, for example a red light, a dew heater controller, a second camera or a mirror.

Got a Telrad base on the tube? The adapter can also drop into its two cups instead of the Telrad. No suitable finder shoe at all? Then take the universal V-block: it sits on any tube and is held with two cable ties or hose clamps.

What you need

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Finder shoe adapter 3D print

For Explore Scientific or Vixen/Synta finder shoes, a Telrad base, or as a V-block for any tube. Configure and download below.

Only for the V-block: 2 cable ties or hose clamps

Long enough to go around the tube, up to 9 mm wide by default (the channels are adjustable, also for wider straps). A strip of rubber or foam under the V protects the tube’s paint.

Aluminium Picatinny rail with T-nuts, at least 13 slots

About 13 cm or longer, so there’s room for the holder and more. The T-nuts slide into the slot of the printed adapter; the hole spacing doesn’t matter. Picatinny rail on Amazon

Picatinny camera mount

Clamps onto the rail and carries a 1/4" camera screw. Picatinny camera mount on Amazon

Phone holder with 1/4" thread

Holds the phone on the camera mount. 1/4" phone mount on Amazon

Building it

1. Print the adapter

   Choose your mount type below, set how far the rail may reach forward and back, and download the STL. Print it as it comes, slot face on the bed: no supports needed. PETG or ASA hold up better than PLA in the cold and in a hot car; 4 walls and 20–30 % infill are plenty.

   Enter the outer diameter of your tube. With these settings the V-block takes tubes up to 283 mm. A 230 mm tube rests on both flanks, with its two contact lines 30 mm apart. A flatter V (larger angle) suits thick tubes, a sharper one thin tubes. Pull the straps through the channels and around the tube, tight but without crushing anything.

   The two feet drop into the cups of the Telrad base and are held by its thumbscrews, just like the Telrad itself. The default sizes are measured from the cups of “Telrad Mount for Orion Dobsonian” by CHenryInSD (CC BY). Compare them with your base: the distance between the cups, the size of their opening and how deep they are. If the feet sit loose or tight, change the foot length and width by a few tenths.

   Vixen/Synta shoes differ by a few tenths of a millimetre. Measure the slot of yours, adjust the dovetail and print a short test piece first (foot length 20 mm, no overhang).

2. Screw the rail onto the adapter

   Slide the T-nuts of the rail into the open slot of the adapter, put the rail on top and screw it down. The hole spacing of the rail doesn’t matter, the nuts go wherever the holes are. Let the rail reach towards the opening of the tube.

3. Mount the phone holder

   Clamp the camera mount onto the rail and screw the phone holder onto it. Lock it with the knurled ring so it can’t turn. The phone stands upright, its back camera looking towards the opening of the tube, roughly parallel to it. It doesn’t have to be exact.

4. Set up Zenigo

   Keep Settings → Telescope → Pointing on Camera. Then locate once and set the eyepiece point on a bright star. As long as nothing moves on the rail, it stays valid for the next nights too.

A long rail is a lever on the small clamping screw of the shoe. If it wobbles, add a strap around the tube at the far end of the rail. With the V-block, keep the rail’s overhang short or make the block longer.

Finder shoe adapter

The foot for Explore Scientific copies the original ES adapter, including its stop notch. The V-block has channels across it for cable ties or hose clamps; they close towards the V with 45° slopes, so they print without supports too. The base carries a slot for the T-nuts of the rail, sized for 20-series “slot 6” nuts; if yours differ, adjust it under T-slot. The cavity closes with two 45° slopes, so it prints without supports.

The adapter is a JSCAD design. To change more than the sliders allow, open finder-adapter.jscad.js in the JSCAD web app.