CELESTRON STARSENSE EXPLORER DX 102AZ
This telescope’s innovative technology provides the simplest and quickest solution yet to finding objects to observe
The mounting of the DX 102 is completely manual, with flexible rods to allow what are called slow motions providing a finer control over the movement than simply pulling and pushing the instrument. The extra ingredient over a standard manual mounting is the attachment for a smartphone, directly fixed to the central assembly. This is not to be confused with smartphone attachments that simply enable you to take photos of bright objects through the eyepiece, as found on some other beginners’ instruments.
This is an achromatic refractor with a 102mm doublet lens composed of two different types of glass. It has a focal ratio of f/6.5, which means that it has a comparatively short tube for its diameter – a situation that provides a wide field of view and bright image with a fairly compact instrument. Achromatic implies a freedom from the false colour that bedevilled refractors in the very early days of telescopes, but this is a comparative term. Like other achromatic refractors, the instrument still has some false colour, which shows as coloured fringes around the edges of objects, particularly at high magnification, and the short tube results in inherently more false colour than an achromatic instrument with a longer focal ratio. To completely overcome false colour you need a considerably more expensive apochromatic refractor or a reflector. However, refractors are traditionally more robust than reflectors, so there is no ideal instrument to suit everyone.
The package comes with two eyepieces, giving two useful magnifications of 26x and 66x, and what is termed an erect-image diagonal. A star diagonal is standard with astronomical refractors, and reflects the beam from the focuser through 90 degrees to allow a much easier observing position than crouching on the ground looking up through the tube, but usually it has the drawback of reversing the image, as in an ordinary mirror. The diagonal provided by Celestron uses a roof prism rather than a simple mirror, giving a non-reversed image so you can use the instrument by day as well as by night. It also avoids the confusion of viewing the Moon’s features or starfields back to front. Finally, there is a standard red-dot finder to help in pointing the telescope at objects. This is necessary when aligning the telescope, as you need to point it at a recognisable object at the start of observing.
The instrument comes in just two main parts – the tripod and the tube assembly – so it seems straightforward. The accessory tray that sits in the middle of the tripod legs, however, needs to be attached by fiddly little thumbscrews that are already
in place, but the wrong way round. This is poor design, as these screws will quickly get lost. A simple slot-and-turn system would be much less aggravating, unless you intend to use the instrument solely as a piece of furniture set up in the corner of the room, or do without the tray altogether. The telescope attaches to the mount using a standard dovetail, but as it came out of the box the clamp assembly was twisted through 180 degrees, with the locking screw at the bottom. The instructions tell you to turn it, but this is easier said than done. Many beginners will wonder if they are meant to be forcing this round at all. In fact, you do need to apply a lot of force to twist it. Confusingly, the instructions then refer to the knob at the bottom of the clamp.
Once set up, you need to align the reddot finder with the main instrument by day. Unfortunately, the adjustment range on the device supplied did not allow it to be aligned accurately, and for the test we used another that we already had. The final step is to remove the cap from the mirror on the StarSense dock – again courageously pulling it off with some effort – and fitting your smartphone into the spring-loaded slider. Bear in mind that not all smartphones will work, and check your model against a list on the Celestron website before taking the plunge. It must have a camera sensitive enough to image the brighter stars using a
“Provides a wide field of view and bright image with a fairly compact instrument”