With the Sun setting earlier and rising later, we can think ahead of the upcoming lovely autumnal and winter Milky Way splendours we can view and image. However in the meantime we have the two largest planets in the Solar System, Jupiter and Saturn, dominating our evening skies. Although both planets are low down in the sky here in the UK, they are still worth pointing your telescope towards.
Telescopes such as Celestron’s SLT 5″ or SLT 6″, with their aperture and long focal length, are good telescopes for Lunar and planetary viewing – but what about eyepieces?
Celestron do a range of eyepieces called the X-Cel LX series that are ideal for observing the Moon and planets, as well as a wide range of deep sky objects too. Two X-Cel LX barlow lenses, a 2x and 3x, are also available to complement the eyepiece range, and we will cover these in a later blog. The eyepieces come in focal lengths of 2.3mm, 5mm, 7mm, 9mm, 12mm, 18mm and 25mm, and all have a 60º apparent field of view. Each have 16 mm of eye relief for comfortable viewing with or without glasses, and they are all parfocal (which means you can swap different X-Cel LX eyepieces with little or no focusing adjustments required). Internally they have 6-element optics with multi-layer high-transmission coatings for maximum light throughput, and the lens’ edges are blackened for increased contrast. The eyepieces are neither too large or heavy with their size (length) and weight being between 84mm and 207g (for 25mm model) to 110mm and 213g (for 2.3mm model). The eyepieces all have a maximum diameter of only 48mm (including the middle rubber grip), and so can be used (in same focal length pairs) with binoviewers.
A lot of similarly priced or cheaper eyepieces have thin rubber fold forward/back rubber eyeguards which, over time, can perish. The X-Cel LX series feature a thick rubberised twist up/down eyeguard for easy adjustment (and longer life) with an “notched” outer edge surface for better grip. The top surface is flat which suits the majority of observers who wear glasses. Furthermore, this flat surface also makes a good “interface” between the eyepiece and a smartphone should you want to take a photo of the Moon and/or planets using the Celestron NexYZ smartphone adaptor too.
The main body of the eyepiece has a wide tread-style rubber pattern around the mid-section for improved grip even when wearing gloves during the cold season. This makes picking the eyepiece(s) out of your storage case or swapping eyepieces easier and safer. The eyepiece barrel exterior has an undercut and, as with all of Celestron’s eyepieces, the barrel interior is threaded to accept (1.25”) filters.
To work out what magnification you will get with an eyepiece, simply divide the focal length of your telescope by the focal length of the eyepiece. For example a 6″ SCT with a 1500mm focal length with a 9mm eyepiece will give ~167x magnification. However don’t get carried away with magnification. It is often said that “under [turbulent] UK skies” about ~250x magnification is often considered to be about the maximum. If you over magnify the image, it will become dim, but also “soft and blurry”. Having a range of eyepieces with different focal lengths (and thus magnifications) can allow you to select the best eyepiece magnification for your telescope for the sky/atmospheric conditions at the time.
Below is a simulated image from Stellarium of the approximate field of view you would get if you pointed a Celestron C8 SCT telescope at Jupiter and used a 9mm X-Cel LX eyepiece. This configuration would give a magnification of ~225x. Jupiter’s bands would be easily seen as well it’s moons. The final “real-life” view you would see of course with such a set up would be dependant on the atmospheric conditions and if your telescope was properly collimated.