wpo - review : Celestron 8-inch [20cm] Ultima 2000 SCT
astro-optics pagetext
& images [c]Maurice Gavin 1997/2001- Astronomy
Now 1997 May issue page 55/56
The Celestron 8-inch Ultima 2000
telescope, a top-of-the-range computer controlled SCT
is reviewed for Astronomy Now by
Maurice Gavin
In
the aperture-fever stakes it is nice to have a telescope that is both powerful
and manageable. The Celestron 8-inch Ultima 2000 is Celestron's top-of-the-range
SCT under full electronic control and it took just a few minutes to set
up the tripod, locate the telescope base onto the tripod's raised steel
pin, secure it with three locking bolts and start observing.
The Ultima comes in three cartons: the complete fork mounted optical tube assembly and drive system, the assembled tripod and a smaller box with accessories and manual. The telescope is contained in a handsome and sturdy black PVC foam lined travelling case with pockets for accessories. The accessories include the controlling hand-set, 7 x 50mm finder, 1.25-inch backplate adapter and star-diagonal, a 26mm focal length (fl) Plossl 1.25-inch push-fit eyepiece and Allen keys for collimation etc. The single x80 power eyepiece gave excellent views but the user will soon need at least a good second eyepiece (say about 10mm fl) and a x2 Barlow lens. This will give powers of x80, x160, x200, x400 - the latter reserved for those perfect nights.
Another vital accessory is a dew cap as the exposed front corrector plate, in common with all SCTs, will dew-up at the least provocation at night. The focusing knob has a nice positive grip and was silky smooth in operation. Some mirror 'slop' was evident as the focusing knob was turned back and forth which caused a horizontal image shift of about 30 arc-seconds. This is acceptable and of little concern for visual or photographic use. The optical tube assembly, finder and cover plate to the electronic 'brain' in drive base have a handsome silver grey anodised finish with a raised logo. The collars to the tube and the drive base have a fine black etched finish. The glossy black crackle finish to the sturdy fork assembly of cast aluminium was somewhat less impressive with some sharp exposed edges. The forks include two strong silver anodised handles for carrying the instrument to the tripod. The collapsed tripod occupies a modest 2.5 cubic feet.
When the legs are spread and braced, the tripod is very sturdy and adjustable in height from 5ft to 2.5ft. The latter was particularly effective from a relaxed seated position. The tripod has a black etched finish like parts of the telescope. The rubber feet, apart from giving a good grip on smooth surfaces, absorbed vibration much better than my permanent pier-mounted telescope nearby. However in common with most portables, jarring the telescope will temporarily spoil the view.
The finder is
of sensible size and gave nice clear views perfect for its task. It is
secured by two rings - one adjustable - and can remain on the telescope
when stored in its case. In addition to the simple crosshairs at the eyepiece
focal plane, this finder incorporates a circular graticule divided into
24 sections like a 24-hour clock face. These are used during polar alignment
in equatorial mode and represent the offset of Polaris from the true north
celestial pole. The on-board computer remains active even when the power
is switched off. Power is supplied by eight AA replaceable batteries
which pop into two covered recesses in the telescope base. The batteries
(to quote the manual) will last about 20 hours in use and the handset will
reveal their status and current voltage. The telescope can also be
powered by an external 12VDC supply such as a car battery and an input
socket is included. A phono socket and lead are included for controlling
the Ultima remotely.
Balancing act The Ultima needs to be carefully balanced to ensure the small motors are not stressed. Two fixed weights are permanently mounted on one of the forks for horizontal balance whilst a sliding weight along the underside of the tube balances the vertical axis against changes of eyepiece, star-diagonal or dew cap. A set of four smaller additional weights are included as standard and should balance heavier items like a camera, although this was not tested. As the telescope is factory balanced horizontally there is no locking nut or mechanical knob to provide centring adjustments on a target. This has to be done via the handset, once the correct tracking speed is set. I found this irritating as just manhandling the pointing was too crude. A locking nut to the vertical (up-down/declination) axis applies sufficient friction to ensure the motor drives engage.
The Ultima's built-in computer uses the two star option to visualise the complete sky and works in both altazimuth (horizontally and vertically motion) and equatorial systems. The Ultima has abandoned setting circles (denoting RA and declination in equatorial mode) and has no bubble level to set the tripod precisely level. An equatorial wedge was not supplied for this review so the telescope was tested in altazimuth mode only. This is perfectly acceptable for visual observations and proved very convenient, especially when seated. With the star-diagonal in place, viewing any object no matter where in the sky, remained in a relaxed downward direction. In this altazimuth mode the field-of-view rotates slowly (once per day) but sufficient to blur photos hence the need for a derotating prism. A more cost effective solution for amateur astro-imaging is to mount the telescope on an equatorial wedge and align the instrument on the celestial pole.
Under control The small controlling handset fits neatly into the palm and a short coiled phone-lead plugs into the base console. All prompts are clearly visible on a two line 8-digit red LED screen. The LED brightness is adjustable but illegible in daylight where it would be nice to get familiar with the controls. The few buttons are raised and have a nice positive feel: one each for slewing the scope in any direction i.e. up, down, east, west, and four for menu selection. The latter are cycled and fairly intuitive.
Initially the telescope tube is inverted downwards to a stop and aligned to two markers on the base. From the menu a bright star is selected. The telescope is manually aimed at the star which is centred in the eyepiece. This is repeated for a second star. Alignment is then complete. The handset warns if the second star falls outside its error box or if the telescope was aimed at the wrong star. Accompanying the telescope is a set of simple monthly star charts which give adequate guidance on star selection. After perusal of the manual (A4, 126 pages) even a newcomer to the sky will have little difficulty programming the telescope.
Some 10,000 deep sky objects plus all the planets from the Sun outwards are included in the computer memory. The handset warns when the Sun is selected or when any object is too close to the Sun to be either seen or safely observed. The options available through the handset are very comprehensive. Included are PEC (periodic error correction), battery status/voltage, eight tracking speeds (slew, finder, centre, x2 sidereal, sidereal, solar, lunar, king), locate stars, planets and deep sky objects through name and catalogue number and much more.
I chose Vega and Altair in the west as my alignment stars and cycled through the menu of planets to Saturn then rising in the south-east. Entering the date and GOTO brought Saturn into the field-of-view moments later. A nudge or two on the control button centred it. In moments of good seeing the crisp ring shadow on the ball of the planet was visible together with subtle cloud belts. Four satellites were immediately seen, two very faint and close to the ring system. Thereafter I targeted a selection of deep sky objects which Ultima found with relative ease.
The precision with which the Ultima centres a target and tracks it during the observing session is very dependent on the care taken with the initial two star alignment so it is worthwhile doing this carefully. On a second occasion the Ultima was left tracking Saturn for over two hours and throughout this period it remained centred in a medium powered eyepiece. The test was only concluded when the planet could no longer be seen through increasing cloudcover. Admittedly Saturn was on the southern meridian arcing due west so, in theory, the computer and motors had the easy option. When following an object rising in the east (or setting in the west) the telescope tracks a series of minute step-like motions that appear smooth. Of course guidance for prime focus photography is an order of magnitude more demanding than the most critical visual tracking and there is no reason why the Ultima would not be up to the task.
On tour Of particular fun was the tour option. In auto tour mode, a month is selected and the telescope instantly starts zapping all over the sky through a series of up to 40 deep sky objects. This is fast and furious; once the scope has slewed to a target (just a few seconds) you have about ten seconds to peep through the eyepiece before it slews to the next object. But if that next object is lower in the sky, then the eyepiece would move upwards poking you gently in the eye if you don't move out of the way. In this mode, which is mainly for demonstration purposes, the Ultima assumes you are on a mountain top with clear horizons in the mid-30s latitude (to satisfy USA southern states) and will amusingly point to local obstructions like your home, garden fence and the ground during the tour. The visual tour mode allows the observer to tell the computer to move to the next selected object when ready.
There is no denying that the Ultima has personality. For example after viewing Vega, I selected the nearby epsilon Lyrae (the double double) and the telescope chose to perambulate the whole sky through 359 degrees west rather than move just one degree east! This apparently is a safety feature to stop the cable tangling. Following a clearing rainstorm the Ultima gave me some of the best views I can remember of old faithfulls like the Ring (M57) and Dumbbell (M27). Globulars were nicely resolved into a myriad of stars.
Was this only an 8-inches aperture telescope? I'm sure the Starbright enhanced coated optics was a major factor in giving bright, high contrast images with nice diffraction patterns around stars at high power during moments of good seeing.
The Ultima been some time coming but Celestron
now seem to have got it right. Whether you need a computer to find your
way about the sky depends on your interests. If they are confined
the Moon and brighter planets then the premium expenditure would be unjustified.
If, however, your interests are more far-reaching, then a computerised
telescope will increase your ability to target objects perhaps ten fold
(especially in light polluted skies) and make much better use of your observing
time.
Available from:
David Hinds Ltd., Unit 34, The Silk Mill, Brook Street, Tring, Herts HP23 5EF
Tel: 01442 827768; Fax: 01442 890763
Price £2599 incl VAT; carriage and insurance £24 extra [early 1997].
Maurice Gavin is BAA President and edited Astronomy Now's CCD Sky column for many years.