Polarscope Illuminator for the Sky-Watcher Star Adventurer 2i

The Sky-Watcher Star Adventurer 2i is a tracker for Astrophotography. It can be used with a camera to track stars, the Sun or the Moon across the sky.

If you read the online reviews of the tracker you will notice that there are a few niggly little inconveniences with the design. One of them is the polarscope illuminator which is a separate item that contains a battery and red LED. This is rather inconvenient as it is fiddly to fit and use. It is also easy to forget it, loose it or drop it!

This instructable provides a more convenient solution based on luminous tape, which glows green for a few minutes after it has been exposed to light.

Supplies

I measured the polarscope hole diameter and depth, designed it with the free DesignSpark Mechanical CAD package and made the illuminator body using a 3D printer. It would also be possible to make one to fit using plastic and conventional means.

The illumination is provided by luminous tape, this is sold by various online stores and is available in craft stores. Ideally a red luminous tape would be used to avoid affecting the "night vision" adaption of the eye, but green seems to be the only colour that is bright enough for this particular purpose.

I contemplated buying "glow in the dark" 3D printer filament but could not justify the cost for a small project like this.

Make sure you do NOT buy "fluorescent" tape as that does not "glow in the dark" when the light is removed.

Safe luminous paint can also be used instead of tape.

The 3D printer compatible stl file for the illuminator body is included here:

Polarscope_v2_illuminator.stl
Download View in 3D

Step 1: 3D Print the Holder and Attach the Luminous Tape

After 3D printing the illuminator body, the 6mm disc of tape and 1mm wide strips are attached. The illuminator is then slid into the aperture at the end of the polarscope and gently pushed in. It is designed to slide in to the locking ring of the lens and not touch the lens.

Depending on the tolerances of your 3D printer you may need to scale the stl file in Cura so that it is a sliding fit in the polarscope aperture without being too tight to fit, or too loose to fall out.

Step 2: Activating the Luminous Paint

Shine a phone torch or LED head torch into the polarscope eyepiece, the light will fall on the luminous tape and activate it. The tape will typically glow bright enough for a few minutes to allow time for polar alignment.

It is handy to use a phone torch as it is likely you will be using one of the phone Apps that show where the polar star(s) should be placed in the reticule anyway. The App I use is called "Polar Clock".

In the picture above the dust cap is removed, but it can be left in place while the tape is being activated.

Step 3: View Through Polarscope

The polar alignment reticule will be illuminated as shown above. If polar alignment takes more than a few minutes you can reactivate the tape again with a torch.

The illuminator blocks a small amount of light (about 20%) entering the polarscope but it does not obscure the view due to the close proximity to the front lens element. Experiments indicated that a central luminous disc gave the best reticule illumination brightness while minimising the light loss in the sky view. The Sky-Watcher polarscope does have a good 20mm aperture so the sky light loss is not significant.

The alignment stars in the Southern hemisphere are quite dim, so in this case it may be necessary to wait until the illuminator brightness fades (a minute or two after activation) or reduce area of the tape, perhaps by not fitting the radial strips of tape.