Lidl Skylux 379 Optus refractor telescope

Introduction

In January 2003 I bought a cheap telescope from a UK branch of Lidl, a German based cut price supermarket that has weekly special offers on all sorts of stuff. Although the usual advice is never to buy a telescope from anywhere but a specialist dealer, I thought that £79 was not a lot to gamble on what appears to be quite a well specified cheap scope.

The "Skylux 379" is a 70mm aperture refractor with a focal length of 700mm. It is supplied with a 6x30 finder scope and an equatorial mount on an aluminium tripod. Eyepieces (1.25") are 20mm and 4mm Kellners. Lastly a star diagonal and a 1.5x erecting lens are also included.

After buying the scope I did some web searching and found a lot of similar scopes under other brand names. A very similar scope appears to have been sold before by Lidl in Germany, but called "Optus". Here are some of the web sites I found with a Google search (most of them are in German):

Mechanical improvements

Focuser

The first improvement I made to my telescope was to clean, modify and lubricate the focuser. I was given courage to start dismantling by a German web page describing how to remove a baffle from the focuser. I recommend you look at this page before dismantling the focuser, as it has some good photographs. I found that my focuser does not have the 12mm obstruction described (it has an 18mm one), so no drastic surgery is required. I checked this by placing an SLR camera at the "prime focus", pointing the telescope at a bright outdoors scene and looking through the camera's viewfinder while winding the focuser in and out. No vignetting was visible, and the camera's TTL meter reading didn't change.

Dismantling

Start by firmly clamping the telescope mount, or removing the telescope from the mount and placing it on a level surface. Removing the focuser will unbalance the scope, and you don't want it swinging around when you least expect it. Undo the three screws at the end of the telescope tube, then slide the focuser body out. Next undo the two screws that hold a black metal cover over the focuser control shaft and remove the cover. This reveals a U shaped brass part that holds the pinion shaft in place. Remove this brass part and the pinion shaft. The chrome coloured draw tube can then be slid out of the focuser body.

Cleaning

The focuser rack and pinion as supplied are "lubricated" with a thick, sticky grease that is also used in the mount. I cleaned this off with "Gunk" (an engine degreaser - I don't know its composition but it has the warning "contains cresylic acid" on the tin) and an old toothbrush. All parts need a good scrub, followed by thorough rinsing and drying.

Adjustment

Temporarily insert the cleaned draw tube into the focuser body and test it for wobble. Mine had a lot of play, which I reduced by sticking packing pieces to the inside of the focuser body. I used some self adhesive hard plastic sheet from which I cut small strips. I used three pieces - two at the outer end, ±30° from diametrically opposite the rack, and one at the inner end, diametrically opposite the rack. The idea of using three pieces is to provide a stable support for the draw tube.

A crude way of controlling wobble is to have the pinion spring loaded against the rack, pressing the draw tube against the opposite side. The slot in the focuser body that holds the control shaft wasn't deep enough to allow this, so I made it deeper with a small file, taking care not to make it any wider, as this would increase backlash on the control. I also reshaped the brass U piece by bending its "wings" up slightly to provide some spring action.

Reassembly

Smear some grease on the rack, then slide the draw tube into the focuser body. Grease the pinion and the adjacent parts of its shaft, then place the shaft in its slot, followed by the brass U piece. Put the black cover over it and insert the two screws, but do not fully tighten them. These screws can be used to adjust the stiffness of the focuser action. Slide the focuser body into the telescope tube, aligning the three screw holes, and replace the three screws.

All this mucking about with the focuser left me thinking that a sliding draw tube is not the best way of doing it unless you use precision engineering. So I've invented an alternative (but I haven't made it yet).

Tripod

The only improvement I've made to the tripod is to fill the lower legs (the bits that slide out of the clamps at the ends of the upper legs) with dry sand. This is very easy to do:

  1. Undo and remove the small screw at the top of the lower leg, taking care not to lose the two washers that pad it out to make it into an end stop that prevents the lower leg falling out.
  2. Slide the lower leg out of the tripod.
  3. Remove the plastic bung from the top of the lower leg.
  4. Fill the lower leg with dry sand, tapping the leg on the ground to shake the sand down as you go.
  5. Replace the plastic bung.
  6. Slide the lower leg back into the tripod.
  7. Refit the screw and its two washers to secure the bung.

Mount

The main problem with the mount as supplied is that the slow motion controls are very stiff to turn. This is mostly caused by the very sticky grease used to lubricate all the moving parts, but I also found that all possible adjustments were on the tight side. I believe the mounts are made like this to disguise poor manufacturing tolerances. I've greatly improved my mount by dismantling, cleaning, greasing and reassembling it.

On one of the many German websites about the Lidl telescope I read that its mount is equivalent to the "EQ2" sold with many different brands of budget telescopes. Pictures of the EQ2 show it also has a gear wheel on the right ascension slow motion control shaft, so I decided to buy a 2nd hand EQ2 clock drive to use with my Lidl telescope. When the drive arrived I was surprised to discover that it is designed to work with a mount that is the mirror image of the Lidl mount.

After some more web searching I found that the Lidl mount looks very similar to the "LOMO 9020 equatorial mount" or Teleskop-Service's "TS Astro 3". Comparing it with the Optical Vision EQ-2 mount shows that they are indeed of opposite chirality. However, the EQ2 clock drive does fit, after removing the tensioning spring and sliding the gear to the very end of its shaft. Although I'm in the northern hemisphere, I needed to set the drive's control box N/S switch to south!