Scope review by Maurice Gavin www.astroman.fsnet.co.uk...my homepage ..Ewell AS homepage. my spectro books
review of Bresser Skylux telescope - Lidl stores £49.99
There's
been much publicity on Internet newsgroups recently regarding the seasonal
release of telescopes at UK Lidl Stores - in this case the Bresser Skylux
70mm f/10 refractor. Mine was bought locally when the shop opened on release
day Dec 15th. The telescope comes complete with metal equatorial
head and adjustable tripod - worth the price alone! All the screws
are chromed metal. The remainder of the 'scope is plastic but
seems quite robust although you are advised in the Instruction Manual [in
6 languages] to avoid undue tensioning of locking screws etc. The
main tube and finder are coloured 'Meade dark blue' - all remaining non-chromed
surfaces are semi-matt black.
The
optical tube
The plastic telescope tube
has a large and extended fixed dew shield with cap. The metal drawtube
has a rack and pinion focuser and accepts standard 1-1/4 inch pushfit eyepieces.
The drawtube is pretty rigid and receives my 750g Canon 300D DSLR in lieu
of an eyepiece without complaint. The drawtube has two locking screws to
secure eyepiece or camera - an excellent idea.
The internal surfaces within the drawtube [and star-diagonal] are bright chromed and can introduce extraneous glare when viewing the moon. It's easily resolved by the user securing thin matt-black card over the offending surfaces.
The OG is quoted as 70mm aperture and 700mm focal length and I've no reason to doubt it. If the OG is coated it reveals little evidence of such on casual inspection. Viewing down the tube from the OG shows no vignetting of the full bore of the 1-1/4 inch drawtube indicating no internal stops are blocking the 'scope's full 70mm aperture - a trick played by lesser manufacturers to improve optical performance. One [and maybe a second] tube stop blocks off-axis light bouncing off the tube inner walls into the eyepiece.
Solar
observing
The Manual wisely advises
against any solar observing with the telescope. Due to the plastic tube
construction it's equally unwise to project the sun's image onto a card.
Any slight misalignment could melt the tube internally! A secure
full aperture solar filter over the OG [finder capped!] is the only safe
way to observe the sun and this will be amongst my prime uses for the Skylux.
Equatorial
head and tripod
These are all metal construction
and robust. The rigid tripod has adjustable legs and rubber feet
with a solid plastic eyepiece tray locking legs apart. When deliberately
tapped vibration stopped a remarkable couple of seconds later when an object
was viewed through an eyepiece.
The head [less counterweight] weighs 630g and has provision for rotation on the tripod in azimuth and altitude - the latter is set to the user's latitude via a cam. RA is divided at 10 min intervals and Dec at 3.3o and each axis has a locking key to its shaft and hand slow-motion knobs *-these are poorly located and foul each other in specific positions*. A 96 teeth 50mm diameter chromed wheel on the RA axis slow-motion worm [*@ 6 r/p/hr*] presumably takes an optional drive motor.
The plastic 'scope cradle is secured to the Dec axis with a single locking screw and opens to receive the telescope tube. The head is clearly designed to receive a larger cradle and telescope perhaps up to a 100mm refractor. The Skylux tube is slid for-and-aft on a felt liner for balance. The sliding counterweight on the opposite end of the Dec shaft balances the whole set-up.
Finder
The
5 x 25 finder, with cross-hairs and rubber eyecup clips onto the seated
recess on the main telescope. It's adequate, if easily dislodged
and is adjusted with two set-screws against a spring. *Belatedly
'discovered' [and not mentioned in Manual] the finder gives a covenient
view where 'up' is to the top - probably via an internal erecting lens*.
Eyepieces
The telescope comes with
three simple but adequate eyepieces of 20mm, 12mm [both with rubber eyecups]
and 4mm focal length giving nominal powers of x35, x58 and x175 respectively.
All the eyepieces are nearly, but not quite, parafocal which helps when
swapping to a higher power. Small extensions to the collars could
make them parafocal when used with say the star-diagonal. Surprisingly
the 4mm eyepiece worked quite well on planet Mars and some adjacent close
double stars. No Barlow lens is supplied but a Barlow-like
tube containing a small deeply recessed 12mm diameter lens is.
It proves to be a x1.3 erecting devise so the [terrestrial] world is the
right-way-up! It's pretty useless but presumably included for the
general public unfamiliar with the upside-down world of telescope viewing
- I've already converted
mine to a simple spectroscope. An ever-useful star-diagonal to
avoid stargazer's cricked-neck syndrome is included and seems of fair quality.
Under
test
After assembly, which was
straightforward, the telescope was tested on a few sky objects in hazy
conditions. The tripod was set-up on my patio with the polar axis
roughly aimed in the direction of Polaris. Regular tweaking the RA
and Dec knobs kept Mars centred even in the high-powered x175 [4mm fl]
eyepiece. With the lowest power x35 the field is ~1o across - the
Full Moon had plenty of space around it and could drift across the field
for maybe three minutes before recentering.
The
OG reveals some chromatic aberration [CA=colour fringing] around bright
objects as to be expected for a simple 2-element achromat. Somewhat
disappointing was evidence of spherical aberration [SA] e.g. inability
of inner and outer zones of OG to come to a common focus. This produced
a slight fuzz on high powers around bright objects like Mars but was less
obvious at low powers or the Moon which is probably the most tolerant of
all sky objects. It needs further investigation. There was
no evidence of OG astigmatism.
The eyepieces, especially the 4mm, added a slight prismatic colouring of their own but it's at minimum with an object dead centre. Curiously this eyepiece colouring can be put to good use. On this evening with Mars at least 40o altitude, prismatic dispersion caused by the Earth's atmosphere was clearly evident under high power. However if Mars was shifted slightly below field centre, the atmospheric dispersion and eyepiece CA cancelled each other out for a sharp colour-free view! This trick was used decades ago by planetary observers before the wonders of highly corrected widefield eyepieces.
Extras
Apart from the concise but
adequate Manual, there is a simple Moon map, planisphere and Skylux starchart
CD [not tested] for Windows 95-XP.
Maurice Gavin aka Nytecam
