DIY Polar Scope Illuminator for EQ5 Mount

I recently bought a 2nd hand Sky-Watcher Explorer 200P on an EQ-5 mount off AstroBuySell and was pleased to discover that it came with a polar scope. For the unitiated, these are used for aligning the polar axis (that’s the extra one that alt-az mounts don’t have) to the north celestial pole so that objects can be tracked by moving the scope in the Right Ascension (RA) plane only. Alignment requires sighting Polaris through the polar scope so that it aligns with a specially engraved reticule inside the polar scope eyepiece. The problem is that when its dark, the reticule markings cannot be seen so have to artificially illuminated (but not too much otherwise it swamps the stars!)…by a polar scope illuminator. Of course, you can buy one at £23 but reviews of them were very mixed so I researched how to make one, after all it’s only a fancy dim torch how difficult can it be?

The description below is really a prototype (with help from utube) as I tried various options while making it. The bought ones fit on the eyepiece but mine fits on the inside the hole in the mount at the ‘objective’ end.

Parts Needed – plastic

From Screwfix, Wickes or Discount Store, Swadlincote

  • 32mm plastic equal tee with compression joints –– about £3.
  • 32mm socket plug – £1.20
  • 40mm socket plug – £1.20
  • 32mm PVC pipe – £2.40 for 3m – we need about 250mm! Try to find an off-cut.

Parts Needed – electrical

From RS Potts Babbington Lane, Derby

  • Small red LED
  • Small rocker switch
  • AA double battery holder
  • 1W rated resistor
  • Small connectors (3)
  • Low voltage cable
  • Insulating tape, or earth wire insulation
  • M4 screw, nut and washer
  • 2 x AA batteries

I had some of these already but I bought the LED, resistor and battery holder for a total of 94p.

Method – refer to photos

Cut the pipe into 2 pieces: 100mm for battery/switch compartment and 50mm for inserting into mount. The longer piece and the branch stub of the tee need to be cut to fit the rocker switch, making sure it faces downwards for easy access when looking through the polar scope. Cut away the flange of the 40mm plug to form a neat end for the battery compartment.

For my mount, I needed to reduce the diameter with a rasp/coarse emery for it to fit snugly inside the hole in the mount. This was a pain by hand but would take only minutes in a lathe.

I made a support (12mm x 150mm but length depends on your mount) for the wires to the LED from a 150mm length of pipe and bolted it to the bottom stub of the tee with M4 screw/nut. Tape wires to the support to keep them out of the field of view.

The 32mm plug is just a cap for the top plug when not in use. My photo shows the branch of the tee curving upwards but it’s better to arrange it curving downwards (remember mine is a prototype!).

Wire up the battery compartment, switch, resistor and LED (polarity is important for the LED). Carefully measure the lengths of wire needed to avoid excess. Soldering is better but I used small plastic connectors. Use tape or insulation to cover any bare wire connections.  Fit the batteries and test. If all ok, carefully thread the wired assembly into the tee piece and your ready to try it out. The support and position of the LED may need to adjusted/bent to avoid it shining directly into the polar scope.

You have a polar scope illuminator for about £10. At the next opportunity, I will attempt to take a photo of the view through the polar scope when illuminated and add to this post. Feel free to ask questions. To finish I would like to hear details from anyone who uses a 90 degree viewfinder on their polar scope, its a long way down to the eyepiece without one.

Illuminator Fitted to EQ5 Mount
Finished Assembly
Exploded View

Eq6 rail mod .

Xmas goodie, overcomes the steel adjustment bolt versus Aluminium mount problem. Shouldn’t be much of a problem if folk supported the weight of the mount whilst adjusting the altitude to get polar aligned. However , eventually the adjustment bolt will begin to make its slippable groove into the mount head. Modern Astronomy used to sell a cumbersome and well overengineered fix.

The rail mod is much cheaper at about £130 and very easy to fix. Takes about 15 minutes , including time to gather a 16mm wrench and spanner.

Heres what you get ,

It’s beautifully made and you get a choice of self adhesive side plates. First job is to remove the existing glued on ones.. I ended up using a soldering iron to melt my way through. Make sure that you’ve marked your zero on the alt. Cover. Loosen the 16mm bolt on this side at the same time as loosening the holding bolt the other side. Slacken off the three 2mm Allen grub bolts. 

Then remove the bolts and gently ease the head apart . Note where the plastic spacers and metal one go. Clean everything up. Grease the mod and insert it , best remove the adjustment bolts first. Then insert the bolts , ensure the rear bolt enters the hole on the rail barrel. Put plenty grease here, metal to metal. Ensure everything is secure , the rail stops and fits exactly into the bed of the mount, easy.

This shows how it works,

Slide the base into the head . Grease on the plates will hold them in position . Ensure the adjusting bit of the head is between the barrel and the front adjustment bolt . Replace the main bolt . Tighten to give no movement if you jiggle the head. Tighten up the retaining nut and snug up the three grub bolts. 

Fix the side plates on , I used a couple extra strips of self adhesive tape.

The stock bolts are soft steel to stop over grauching of their action on the mount head . The rail mod moves the altitude delightfully easily . Use the front bolt just as a stop, it doesn’t need to be overtightened.

There’s a rail mod for the Heq5 mount in the pipeline.

Easy and it actually works. Polar alignment does not have to be spot on for visual observing and alignment . Accuracy here does allow the fov to stay still at high magnifications.

Very pleased to recommend this mod. For those with plenty time and resistance to repetition , there’s a guide on YouTube.


Venus and the Schroter effect

Dichotomy, or half-phase for Venus was predicted to be 6th January but due to the Schroter effect may appear late. This is a phenomenon in which the observed phase of Venus appears less than the predicted phase. As a result, dichotomy (half phase) occurs early at evening elongations, and late at morning elongations. The time difference between calculated and observed dichotomy is about a week. The effect was discovered by the German astronomer Johann Hieronymus Schröter (1745–1816). The cause may be that the region near the terminator is darker than the rest of the illuminated disk.

Here is a rather poor image of Venus from the window-sill this morning.


Here is the general view from this morning (9/1/2019). I didn’t manage this yesterday. Early risers can look forward to the Venus-Jupiter conjunction on 22nd January.

Tegmine and views to Cancer.

Here’s an easy to find and glorious sight. Having finished exploring the overlooked M44 (Praesepe) cluster , scan over to Tegmine (Zeta Cancri) SAO 97645. It’s halfway between Pollux and beta Cancri.

Classically described as a multiple , it’ll open out to give a great triple star. It’s closed down to 1.1″ separation , but the brightness of these lemon yellows gives smaller apertures a chance of opening it up. Comparable to beta Monocerotis, it’s always fun to point out a bright star , then increase magnification to open it up.

Exploring Cancer for similar challenges, I’d check out 57 Cancri , a light orange pair , splitting open 1.5″.

Σ1187 , another orange pair opens up at 3.0″. I can’t leave Cancer without looking at iota Cancri . This wide pair is so colourful that it is a contender for “winter Albireo”. The colours were stunning last trip , better than the other “Albireo” in Canis Major ( h3945) SAO 173349. Although I was seriously diverted by “Hind’s Crimson star ” in Lepus and “La Superba” in Canes Venatici.

A closer look at M44 will show you a few binaries in the buzz of this cluster, these include SLe337,336,332, Σ1249 and Σ1254. My skies can be poor , but most clear nights the buzz of M44 is spottable by eye from the top of Gemini.

As we’re heading off there , don’t forget our most distant Milky Way target , way out of our halo. The faint globular ” intergalactic wanderer” , NGC 2419. It’ll appear as a faint fuzz without easily resolvable stars. It is 300,000 light years from here and the galactic centre, twice the distance of the large Magellenic clouds . I think this is a thrilling sight , quite bright , look for the fish hook of bright stars and head off eastwards. This was with a 4″ Vixen refractor .

Hoping for clear skies ! Nick.

Sap from leaf 6/1/2019

Following are photos from sap coming out of cut end of house plant leaf.

Zeiss IM microscope.

No stain.


x32 objective, Optovar x1 intermediate lens:

x63 objective, Optovar x1 intermediate lens:

x63 objective, Optovar x2 intermediate lens, some sharpening with unsharp mask in GIMP2:

x63 objective, Optovar x2 intermediate lens, further contrast and brightness enhanced in GIMP2: