EQ3-2 Polar Scope Illuminator

I’ve read a few posting by people who have made polar scope illuminators for their EQ5 mounts and as I find aligning my EQ3-2 very awkward thanks to the lack of illumination of the reticle I decided to attempt to build one for my mount.

The initial problem was the size of the polar scope “window”. At 35mm diameter, I couldn’t find anything that would fit inside. Eventually I decided to sand down the outside of some 32mm plastic waste pipe (which has a 36mm outside diameter) and use that. To hold the illuminating LED I also wanted a 32mm tee and end cap. The local builders merchants didn’t have any standard end caps, only the screw-in version, but actually I think that worked out better in the end:

These are all solvent-weld fittings and I felt that the tee didn’t need to stand quite so high on the mount, so I trimmed off all but the last 10mm of the socket on the mount side of the tee. I then offered up the sanded-down tube to the mount and marked the limit of its insertion around the outside of the tube, cutting the tube so the mark was just outside the end of the tee. It was then glued into place (you can just see the mark in the second picture):

I also glued the collar for the end plug into the side entrance of the tee and cut off the moulding on the back of the plug, sanding it smooth.

To provide the illumination I used a 5V red LED with a built-in resistor and soldered it directly across the pins of a power connector socket. I drilled a 12mm hole in the plastic end plug and fitted the power connector to it. As luck would have it, when the plug was screwed into the tee the LED came just to the end of the opening, giving a small amount of light down towards the polar scope without being overpowering.

All that was left was to power it up and try it out. For power I used an old 3.7V Nokia phone charger adapter. Running the LED at slightly lower than the rated voltage also helps keep the light levels down. Here’s the finished item:

Aligning the polar scope used to take ages before I made this because of the juggling of a torch to get just enough light down through the scope window and then needing my hands to turn the adjusters, meaning I was spending plenty of time crouching below the mount contorting my neck to be able to see up through the scope. The viewing position hasn’t changed at all, but now the entire alignment procedure takes about thirty seconds and is so much easier and more accurate. I have recently been experimenting with imaging Mars and found that over four minute imaging runs I was seeing minimal movement relative to the SEC axis. A very pleasing result.

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