REVIEW OF THE ERIDANUS OPTICS EYEPIECE KIT 19/06/2005
Today the amateur astronomer has a large choice of telescope accessories to choose from. The most popular suppliers are the wellknown brand names such as Celestron, Meade and Orion. The telescopes as well as their accessories are marketed and distributed from the USA. A fact that is not that well known is that many of these products are manufactured in Japan and more recently in Russia and China.
The products are then exported to the USA and from there they are distributed worldwide using a brand label.
The ‘One Star’ kit (distributed by Eridanus Optics CC) shown in photo 1 consists of the following:
· A 15mm focal length Plössl with a 1.25” barrel
· A 2X Barlow lens
· A moon filter
· Black carrying case
The three optical components in the kit have no identifying marks to indicate their source of manufacture.
The eyepiece mechanical quality is very high, having the same quality as expected of a Japanese optical product. The barrel of the eyepiece is chrome-plated and has an indentation to prevent the eyepiece falling out should the focuser thumbscrew not be fully tightened. The comparison eyepiece, a 12.5mm orthoscopic from University Optics and of Japanese origin does not have this indentation on it’s barrel and as a result the user must be extremely careful to avoid damage to the eyepiece as a result of the eyepiece falling out of the focuser. The eyepiece also has a rubber ring with a knurled surface giving the eyepiece a nice feel when handled. The eyepiece rubber eyeguard can easily be removed and be replaced if desired.
The Plössl eyepiece is the most popular eyepiece used by amateur astronomers today having taken over from the orthoscopic eyepiece. The Plössl uses 2 doublet lenses instead of a triplet. The Plössl is easier to manufacture and has very similar optical properties to the orthoscopic.
· The focal length is 15mm
· The eyepiece is fully multicoated with antireflection coatings on each air-glass surface.
· The apparent field of view (FOV) = 52°
The Barlow lens is of the same quality as the eyepiece but does not have an indentation on the barrel, as a result extreme caution must be observed when handling the Barlow with eyepiece in the dark. When the Barlow falls out the eyepiece comes out with it. It would have been nice if the chromed barrel of the Barlow lens also had an indentation.
The Barlow lens is useful to have with the popular f4 to f5 focal ratio Newtonians doubling the focal length of the telescope. With the Barlow lens the user effectively has 2 different eyepieces with each eyepiece purchased. With the 15mm Plössl and Barlow lens the user also has a 15/2=7.5mm eyepiece. Future eyepiece focal lengths must therefore be chosen not to be multiples of 2. Normally 3 to 4 eyepieces are enough for observing and the user should initially decide on 3 eyepieces or a Barlow with 2 eyepieces.
The moon filter has a yellow-green color when viewing a white surface. The percentage transmission is 18%. Viewing the moon without a filter is an unpleasant experience especially with a large aperture telescope at low magnifications and a filter is highly recommended. Viewing the moon with the moon filter also gives a more pleasant viewing color than is obtained when viewing with a polarizing filter.
The kit was used on an Orion Atlas 10” equatorial telescope with a f4.8 focal ratio. The telescope is of Chinese origin, being manufactured by Skywatcher(Synta) and being resold by Orion in USA.
Two eyepieces were used to compare:
A 10mm Orion Sirius Plössl which comes standard with the telescope and a 12.5mm orthoscopic of Japanese origin from University Optics in USA.
A side-by-side comparison reveals no difference in the quality of the products.
The Orion Sirius is marked fully coated implying that a single antireflection coating is used on each air-glass surface as opposed to the multi-coatings of the Eridanus Optics eyepiece. The orthoscopic eyepiece is also multi-coated.
Three objects were used for viewing:
In the case of α-Centaurii the double star was viewed in the center of the field and then slowly moved to the edge of the field while being on the lookout for image deterioration. In all 3 eyepieces the image deterioration was dominated by the coma(off-axis image distortion) caused by the main mirror and not by the eyepieces.
It was however noticed that the eyerelief of the Eridanus Optics eyepiece was a bit less than that of the orthoscopic and Orion eyepieces.
Looking at Jupiter the aim was to determine if one of the eyepieces revealed more contrast or detail on the planets surface. Again what the one eyepiece displayed all the others displayed too indicating that the eyepieces are all similar and of high quality.
The moon was used to detect internal eyepiece reflections due to bright sources.
Again the eyepieces performed as if it was the same eyepiece.
Next the Barlow lens was used with the 15mm eyepiece from Eridanus Optics giving an effective magnification of X163 and equivalent eyepiece fl=7.5mm.
The surface of Jupiter was viewed for detail and image quality.
The Barlow was then used with the 12.5mm ortho and then the 10mm Orion Sirius.
It was found that increased magnification improved detail with the 12.5mm ortho but not with the 10mm Orion. The conclusion reached was that 6mm eyepiece focal length is the shortest that can effectively be used with this telescope.
Next the moon filter was tested using another 25mm Orion Sirius eyepiece. The 10” aperture with the X48 magnification and 18% transmission was found to be too bright for comfort when viewing the moon after 1st quarter. Using the higher magnifications of the 15mm, 12.5mm and 10mm without the Barlow solved the glare problem. Viewing the moon through the filter with it’s yellow-green color is nicer than with a variable polarizing filter.
My 1st conclusion was that the quality of the optical products from China is becoming as good as those from Japan and at a lower cost. The complete Eridanus Optics Kit costs the same as a single Japanese eyepiece of similar quality. If you need a 15mm eyepiece the Eridanus Optics Kit gives you a 15mm eyepiece an equivalent of a 7.5mm and a moon filter for the cost of a single eyepiece.