Comments on Sky-Watcher 130 mm reflecting telescope on EQ2 mount.
(Explorer 130M in the UK, SK1309EQ2 elsewhere; mount same as Celestron CG-3)

130 mm Sky-Watcher telescope

Aperture 130 mm (5.1 inches). Focal length 900 mm (f/6.92). Supplied with 25 mm and 10 mm eyepieces (x30 and x75) with 2x Barlow (x60 and x150) though the Optical Vision catalogue claims x36, x72, x90 and x180.

I was pleasantly surprised by the good optical quality of this instrument. Its performance is perfectly adequate for general observation, and while the appearance of Airy discs was not perfect, with rather bright diffraction rings, this was not so bad as to result in poor images. The mirror is spherical rather than parabolic, but at f/7 this is not a big problem. You can also get a parabolic version, the 130P. The stability of the instrument on the mount is adequate, though of course one could always wish for a more stable telescope. As a budget instrument I found it very good for the money.

The finder lets it down it is a stopped-down 6 x 24 finder, and also does not fit properly within the ring that holds one end of it. This is easily put right by winding a strip of tape around the barrel of the finder so that it becomes a tight fit within the holder (see photo), then it becomes possible to align it properly with the main instrument.

One poor aspect of the design is that the secondary obstruction is rather large at 46 mm. The secondary itself is sensibly sized at about 36 mm, but there is an unnecessarily large metal surround to the assembly which must reduce the light grasp and image contrast. This is probably the reason for the brighter diffraction rings that I noticed. Planetary detail would be reduced in contrast as a result.

The collimation of the telescope was perfectly good straight out of the box as shipped. The manual gives instructions for collimation.

One curiosity is that the tube cover supplied has a smaller offcentre aperture in it which you can uncover, with another blank symmetical to it which is fixed. This aperture is not referred to in the manual. It is there to cut down the aperture for solar observing, but in this case the eyepieces are plastic so solar observation is not a good idea and the manual warns you against it. I was pleased to see that the manual also warns against using eyepiece Sun filters, of the sort that were once always supplied with Far Eastern telescopes.

The eyepieces supplied are 25 mm and 10 mm, labelled simply as 'Super Wide Angle Long Eye Relief'. The barrels are plastic and they feel very lightweight compared with, say, the Plössls supplied with Meade telescopes. They are actually modified Kellner eyepieces which do give a wide apparent field of view and have good eye relief. Only an increased amount of false colour from about half way out from the field centre shows that they are not Plössls, but they are quite adequate for general viewing, particularly at the centre of the field of view. The Barlow, however, leaves something to be desired as it introduces noticeable amounts of false colour. Even so, the results are not terrible so it is an achromatic Barlow, and I could see the Airy disc using it with the 10 mm eyepiece. I did get better results when using other eyepieces, so it would be a good idea to purchase a new eyepiece at some stage to get the best out of the instrument. I was able to use a Celestron 7.5 mm eyepiece with 2x Celestron Barlow, giving a good image of the Double Double, with both pairs of stars well separated. Any higher powers should not show any more detail because at this magnification you are simply magnifying the Airy disc even more. The eyepieces did take standard filters, and I was able to view the Veil Nebula using a Meade OIII filter under average conditions.

In conclusion, the Sky-Watcher 130 is an excellent starter telescope which in the UK is sold at a very competitive price. The size of instrument is more than adequate for a wide range of observing, and the powers supplied are sensible.

EQ2 equatorial mounting
This is a German-type equatorial mount on a metal tripod with extending legs. It is adequate for lightweight telescopes up to about 130 mm aperture, though obviously it is a budget mount and you can never have too large a mounting for a telescope. The Sky-Watcher 130 mm tube assembly weighs about 3.6 kg (8 lb) and the counterweight supplied is about the same. When the telescope is balanced the counterweight is only about 2 cm from the end of its shaft so I would not recommend putting a much heavier load on it.

The tripod seems sturdy eough for the purpose intended and the legs will extend to bring the base of the equatorial head to a height of around 1.2 metres (4 feet) above the ground level. For the 130 mm telescope, however, very little extension is needed to bring the eyepiece to a convenient height for observing in most cases. There are collapsible struts across the centre so the legs will fold together if required without having to undo the screws of an accessory tray, though such a tray could be added if needed.

At the point where you attach the counterweight shaft to the Dec axis there is an bolt assembly that is secured by three screws. Slackening off these screws allows you to tighten or slacken the end of the dec axis against a rubber pad, which gives you greater or lesser resistance to moving the telescope around the Dec axis. If this bolt is too loose, the counterweight shaft will sag somewhat under its own weight, so keep an eye on this. It is not referred to in the otherwise good manual.

The setting circles are fairly rudimentary, being pressed metal with the scales printed on. The RA one is calibrated in 10 minute intervals and the Dec one is in degrees, with rather basic pointers. They would get you to the right region of sky, but nothing more. The manual tells you to find a known star and turn the RA circle until it reads the same RA as the star. If you then start the motor drive, the settings should remain correct as the RA circle does not turn with the telescope, though the manual does not point this out. The manual gives you the RA of Vega, but there is no table of the RAs other stars. There is an alternative RA scale for use in the southern hemisphere.

There is a latitude scale on the side of the mount so that you can get your polar alignment approximately correct. But I found that the T-bar used to tighten up the altitude bolt was not adequate to the task without using considerable force, so there is a danger that the whole upper part of the mount and telescope will pivot backwards on the altitude bolt.

The clamps on the axes are quite easy to find in the dark and worked well enough. There are flexible slow motions supplied. In addition, on the RA axis there is a large knurled wheel that is quite useful for moving the telescope in RA. This is actually part of the motor drive system. Anyone who does not have the motor option will wonder about the wierdly shaped metal attachment which swings free. But when you attach the motor, its purpose becomes obvious.

The fitting instructions for the optional RA drive are a little hard to follow, though it is obvious what to do once you realise what is meant to happen. If you have trouble, look at the photograph here to see how it should fit. The motor is held in contact with the large knurled wheel by an extension spring attached to a little thumb screw. The purpose of the odd bit of metal is to act as a clutch for the motor.

You need four D-cell batteries to run the motor -- the sort that are used in large torches (flashlights to the Yanks). These provide a 6-volt supply, though you could use an AC adaptor with a 3.5 mm jack socket output. This should have a positive centre pin and a negative sleeving. It does mean, however, that you can't use one of the popular portable power supplies unless it gives a 6v output as well as the more usual 12v. I don't know how long a set of batteries will last as I didn't start with a new set.

With the drive running and approximate polar alignment, objects stayed in the field of view for about 10 minutes at a time. It may be possible to get better results with accurate polar alignment. When used as a camera platform I could give 30-second exposures without noticeable trailing using a 135 mm lens on the camera. One of the cradles has a stud to which you can attach a camera, which is a useful facility, though a heavy camera will cause balance problems for which the supplied counterweight will not be adequate.

The control box of the telescope has an on-off button, a north-south selector and four speed buttons which allow you to stop the drive, go forward at 2x drive rate., and forwards or backwards at 4x the drive rate. The instructions which come with it refer to 8x forwards and 7x backwards but this doesn't seem to be the case. Curiously, it also says 'When the power is on and all buttons on the control box are depressed, the motor drive will automatically rotate at the correct speed to compensate for the rotation of the earth'. But in fact you only need to switch it on for this to happen.

Robin Scagell, 15 October 2004

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