The PowerMate was a piece of luck in more ways than one. I bought
it as part of a deal, intending to dispose of it – I’d
always disliked barlows. Now it’s one of my favourite and most-used
bits of kit. Now it just happens that the focal length of the C8
(2000 mm) is exactly 2.5 times that of the APO (800 mm), so for the
tests I was able to compare objects with exactly the same eyepiece
giving exactly the same magnification.
The TMB is the bigger of the two when set-up.
Setting The ‘Scopes Up
The Celestron isn’t really so difficult to set-up, easier
than I recalled. It is very compact for an 8 inch telescope. The
tripod is light enough, but awkward to move because folding it involves
turning each leg through 180 degrees. Consequently it stays unfolded
in the garage and moving it involves many near misses with car and
bike paintwork. The frustration has started. The tube/fork assembly
is heavier than any component of the APO and it attaches with three
bolts which are fiddly to get in, despite the original hex-bolts
having been replaced with knurled knobs years ago (otherwise it would
be a real pain!). Surprisingly, once set-up, the Celestron as a complete
unit is lighter and easier to move around the garden than the TMB/GP – one
very obvious plus point for the SCT.
The biggest problem with the Celestron is that it takes ages to
cool down. I have to leave it pointed vertically down with the focuser
tube open to the air for at least a couple of hours before I can
us it. Any observing session which lasts less than three hours is
a non-starter with the Celestron, which is perhaps why it has been
used so little.
The APO is that much easier to get going. The tripod legs fold inwards
in a trice, just like a big photo-tripod. The whole lot goes under
my arm, legs ready-extended with the counterweight attached. Slot
in the dovetail plate with scope attached, tighten a single screw
and we’re done already. A quick squint down the polar-finder
built-in to the GP mount and I’m aligned well enough for visual
use; half an hour later I can start observing. Meanwhile I can still
feel warm air pouring out of the Celestron’s focuser tube...
It’s just two weeks past opposition, so the first object of
study has to be The Red Planet. I have it in the APO’s field
in a few seconds. I don’t bother mounting the finder for bright
objects because the field of view is plenty big enough with the 32mm
TV Plossl - one advantage of the APO’s (relatively) short focal
length. As an aside, I notice how smoothly the GP slews and tracks.
The tripod maybe light-as-a-feather, but it damps vibration well
and is extremely stable. It seems very tolerant of different loads
at the focuser too. I notice these things with pleasure. One real
annoyance, though, is the lack of back focus available – with
a 1.25 diagonal, long focus eyepieces like the 32mm Plossl take loads
of fiddling to get to focus at all.
It’s frustration time back at the Celestron as well. Mars
is centred in the almost-invisble cross-hairs of the finder, but
it’s nowhere to be seen, even with the 32mm Plossl. I spent
ages realigning the finder just recently, but somehow I’ve
knocked it out of line again. Five minutes of sweeping and I’ve
finally got it. But as I’m sweeping I almost push the whole
scope over (my garden is on a slope and the tripod doesn’t
Back with the TMB again, Mars focuses with a pleasing snap. How
I love that Feathertouch! I step up to one of my favourite eyepiece
combinations - the 15mm plossl and 2.5x PowerMate give 133 times
with a nice broad FOV. The seeing is poor, as it often is here, maybe
3-4, but Mars is still really nice. The image scale is small, but
Mars is a sharp disc with lovely colouring and not a hint of chromatic
aberration. The south polar cap is clear and I can see dark markings
on the orange disk.
The Celestron gives, on the face of it, a much brighter view. The
15mm Plossl gives me the same magnification without the PowerMate
in the way. Trouble is the image is all blurry. Actually, the much-derided
Celestron focuser is fine – smooth with little image shift
- but I can’t seem to get a good focus. Mars boils. It can’t
be cool-down time; the scope’s been out over three hours by
now. I assume the problem is the adverse affect of large aperture
and central obstruction in bad seeing. To cap it all, I notice how
unpleasantly jerky the Celestron fork feels after the GP mount.
I repeat the experiment a few nights later when the C8’s had
five full hours to cool. The image is a little better, at least there’s
a trace detail on the disk now, but the TMB still wins easily on
One final go with Mars well past its best almost six weeks after
opposition. The seeing is bad again, but occasionally it steadies
for a moment to give me the best views yet through the APO. Syrtis
Major is clearly visible and unmistakable. The South polar ice cap
has shrunk to a dot in the Martian summer, but it’s clear too.
When the seeing steadies for a moment, I get a mini-Hubble type view
with lovely delicate shading on the surface and the dark area around
the north pole clearly visible.
The C8 still delivers a big, bright orange ball that just hints
at the details the APO shows clearly.
My wife agrees – round one to the APO in these conditions.
A few nights later and there’s a gibbous moon. The sky is
crystal clear, but as so often here in Northern England, the seeing
is mediocre at best. The telescopes are side-by-side and I swap back
and forth with the 15mm Plossl and the 9mm ortho, using the PowerMate
to produce the same magnification in both scopes.
The moon is thirteen days old and I track carefully down the terminator,
concentrating on the Gassendi region, Vallis Schroteri, and Mons
Rumker. I’m expecting the aperture of the C8 to produce a clear
win here, but it doesn’t happen. The first thing I notice is
that whilst the APO can handle 220x with the 9mm, even in the poor
seeing, the C8 simply can’t – it’s a mush. So I
settle for the 15mm Plossl again, giving about 133x.
The next thing I notice is that image is so much crisper and more
contrasty in the APO that it seems the magnification must be lower,
but it’s not. Despite the seeing, the APO delivers superbly.
Shadows are dense, textures are 3d and there is so much detail. There
is no false colour, none – a remarkable achievement by Mr Back
and the Russian opticians at LZOS.
In the C8 the image is much brighter, but there’s less detail.
I keep swapping back and forth over a period of several hours to
check, but it’s true. A white smudge in the C8 resolves down
to a tiny crater in the APO. I see details in Gassendi – rilles,
slumping, craterlets, that are just a smear in the C8. From the domes
of Mons Rumker to the hills and embayments around Gassendi and the
edges of lava flows on the mare near Aristarchus, the APO shows more
Surprisingly, very surprisingly, the APO wins again.
The Double Cluster
The moon has set, so I can try some star-fields and then some faint
Through the APO, the double cluster is a beautiful sight. The stars
are so crisp, the colours so perfect. The core stars are so pin-sharp
there’s almost a 3-d effect and the wide field makes it a more
pleasing view than with the Celestron. There’s no escaping
it, the C8 goes deeper, shows more, but the image is duller and less
pleasing than with the APO. What’s worse, the whole double
cluster won’t fit in the field, even with the 50mm eyepiece.
An artist, at least, would prefer the APO.
The Ring Nebula
I have to lug both telescopes over to the tarmac near my garage
to avoid the trees which are an awkward reality in my garden. I’m
reminded that the Celestron is in fact easier to move.
It’s an overall win for the C8 here, because the Nebula’s
smoky ring is big, bright and easily visible with direct vision;
there’s even a hint of structure. The APO, by comparison, just
can’t keep up. With the TMB I really need averted vision to
see the fuzzy patch as a ring and the whole image is just dimmer
and less convincing. Aperture wins.
My wife points out that what we need is ‘A telescope like
that one [the APO] but with a lens as big as that one [the C8]’.
Who but my bank manager could argue with that?!
One deep sky, aperture wins.
The Andromeda Galaxy
Given that it’s another ‘faintish fuzzy’ the C8
should win here, but, strangely, it doesn’t. True, the C8 delivers
a slightly brighter image at 40x with the 50mm e.p., but for some
reason it’s just a fuzz. By contrast, the APO delivers just
a hint of the galactic structure. Perhaps it’s the wider field
of view in the APO, perhaps the contrast effects of the central obstruction
with the Celestron, I don’t know.
Overall, call it a draw. One thing I do notice, though, is how much
easier the C8 is to use on objects near the zenith. The TMB is a
typical refractor and the eyepiece ends up in some very awkward positions.
My wife simply said ‘Wow!’ the first time she looked
through the TMB at the Seven Sisters. The whole cluster easily fits
into the field of the 32mm Plossl (an e.p. which works superbly with
the TMB) and it’s one of the most beautiful sights available
with the scope. Jewels in velvet etc – you’ve heard it
all before. But, really, the pin-point stars, the perfect colours… The
C8 looks dull by comparison and once again the lack of field-width
lets it down.
Another easy win for the APO on star-fields.
I’m no expert here, but I’ll give it a shot. Polaris
resolves easily in both scopes, no surprise there. The double-double
is much harder. There’s a lot of moonlight on the night I try
it and the image in the APO at 220x is just too dim. The C8 is much
brighter and the stars just resolve into dumbells. Actually, the
stellar images are much smaller in the APO, so maybe under better
conditions it would give a better showing. Jury out on this one and
sadly I’ve no more time to re-run the comparison.
To be honest, I had been kind of hoping to break down the APO myth
a little here. I’d really hoped and expected a Gentleman’s
draw, with the APO producing the finer images and wider fields, but
the SCT trouncing it in reach and detail. It just didn’t work
out like that. Under the poor seeing conditions described, over a
number of nights of careful comparison, repeatedly swapping the same
eyepiece between the two, the APO won decisively. Particularly surprising
to me was the Moon, where I had anticipated an easy win for the C8.
Even hampered by the poorer diagonal (I ended up using the TV everbrite
exclusively on the C8 to give it the best chance) and all the extra
glass in the PowerMate, the APO still produced better images, with
more detail on most of the objects viewed. The C8 only beat the APO
in situations where aperture counted above all else.
The APO is undoubtedly a more pleasing telescope to use than the
Celestron. It’s quick to set up and cool down, giving gorgeous,
crisp images, even in poor conditions. It will give of its best over
a wide range of objects, on days when you only have an hour to spare.
It’s a superb all-purpose instrument, capable of a good showing
on everything from star fields through planets. But none of this
explains why it beat an 8 inch reflector – in theory it simply
At first I thought maybe the coatings on the C8 were the problem,
but no, they are absolutely pin-sharp, like new. Besides, image brightness
isn’t the problem. Then I checked collimation – spot
on. After 3-5 hours of cooling, the Celestron settled and more time
made no difference to the image, so I don’t think the problem
is cool-down. So we are left with just two possibilities to explain
the surprising result of this comparo’: