GTO ZOOM review (short & long :-)

GTO ZOOM Review

In brief

Spec

- US$60
- 22mm-7.4mm (40-60deg AFOV)
- 1.25 inch barrel
- Just enough eye relief at 22mm for when wearing
glasses, eyecup folded down

Cons

- ridiculously cheap
- narrow AFOV at low mag (as with most zooms)
- not parfocal (as with most zooms)
- fussy about eye position for sharp image
- some ghosting with bright objects
- bright yellow tinge around moon
- light halo around edge of field at higher mags
- image wonky at very edge
- eye relief wearing glasses not enough at 7mm end

Pros

- ridiculously cheap
- lightweight and compact
- roll-down eyecup
- surprising sharpness if you hold your head right
- instant hit as “dust cap” ep, ready to go
- visitors have fun playing with mag
- watch that sky darken - a contrast knob for your scope
- with non-tracking scope, zoom out to re-find object
- effortlessly try out and dial up the ideal magnification

The long version

I posted here a few months back asking about barlow+lenses vs lenses only ep
options, and some people suggested considering a zoom. I did the usual fish
around, and came up with price categories of small, medium and large (US$60,
150, and 300+). They all offer very similar specs of about 7-22mm, 60-40
AFOV. I find my SLR’s 28-200mm zoom indispensable, so I figured zooming on
the telescope was worth at least worth a look.

The GTO seemed ridiculously cheap at US$60. However, it gets some
half-decent reviews (e.g. www.excelsis.com). Since I don’t have a try
before-you-buy option, the GTO was the cheap way to check out the whole zoom
concept. I ordered it from Hands On Optical (along with an Anteres 3x
barlow). Well packed and timely delivery.

The lens is compact & lightweight. One reviewer commented on its cheap feel,
but I found it was made of metal and glass and nothing fell off :-) More to
the point, it shouldn’t be prejudged for not being a 1-pound hand-grenade.

Bad points which are standard for this category of zooms, i.e. non-parfocal
(I knew this, a nuisance all the same, though I think some more pricey zooms
might be parfocal?), and 40deg AFOV at 22mm, which I also knew.

My scope is an 8 inch f/6 Guan Sheng dob (sweet unit). The lens barely
accommodated the whole moon in at 22mm, and put a substantial yellow fringe
around the lit edge. It wasn’t there in my GS standard 25mm plossl. This ep
clearly ain’t perfect. But, twist the zoom and…Houston, the eagle has
landed! You fly down towards the surface.

I took some time swapping between my GS standard 9mm plossl (Nagler? What’s
that?) and the zoom dialled in to an estimated 9mm (it has markings at 7.4,
11.0 and 22mm). The moon really is an exquisite object. I got distracted
just cruising around. I picked features that had both fine detail and low
contrast, and swapped back and forth between eps. The GTO seemed to be fussy
with eye position: sometimes it was as sharp as the plossl, other times a
tad off. Might have been ghosting related, though I noticed the same thing
with stars. However it did seem to pretty consistently match or better my GS
25mm plossl on star sharpness.

Images were wonky right at the edge, but pretty flat across the field, even
at 60deg. Mars had a little ghost running around, but no more annoying than
diffraction spikes. I wear glasses and there’s just enough eye relief to
catch the whole 22mm field with the eyecup rolled down. Beyond about half
zoom, the lens gave slight glow around the outer 10%. A few times I thought
I was looking at dark nebula in the middle of the field, except it followed
me around. Annoying but livable.

I’d be interested to compare it to its upmarket counterparts, and to some
premium fixed eps. I started to get used to the 40deg AFOV at low mag, but
dopped in my 12.5mm/70deg WA for a reality check - a totally different
viewing experience. WA provides object context and a sense of immersion; for
me this so important aesthetically.

All that said, the GTO Zoom is a keeper. It instantly became my “dust cap”
ep, sitting in the scope ready for a quick look (the scope has become a
piece of lounge room furniture, sitting inside the sliding glass door and
ready to be lugged out on to the deck in one piece). Roz and the kids like
the zoom; it offers the casual viewer more active participation in the
observing experience through effortless tuning of magnification. Perfect for
FANS 2003 (Festival of Astronomy, North Sydney) a few weeks back. One of the
most striking effects is watching the sky go from grey to black as you zoom
in - a contrast knob on your scope.

A stand-out benefit is when using a manual scope at high mag. If you lose
the object (as you do), it’s very handy to be able to zoom out, pan and
recapture, then go back in. My Mars glass is the GTO zoom + 3x Anteres
barlow, giving a mag range of 164 to 486 (should cover the most freakishly
good seeing). A zoom is nice with an object like Mars: you can precisely
tune the ep viewing conditions.

I did a bit of DSO (galaxy) hunting, and ended up just leaving the zoom in
for most of the night. Partly new-toy novelty, but I was consciously willing
to trade some low mag FOV for the ability to dip in at any time for closer
look. I’m still planning to get a premium 25mm WA; it will be interesting to
see how often the zoom comes out then.

Mark

Mark,

I have the Vixen 8-24 zoom EP, and it is my workhorse. I occasionally=20
pop something else in at the wide end or the low end (Lanthanums), but I =

do use it at least 90% of the time.

My review of the Vixen would be similar to yours of the GTO except for=20
the following items:

- fussy about eye position for sharp image
- some ghosting with bright objects
- bright yellow tinge around moon
- light halo around edge of field at higher mags
- image wonky at very edge
- eye relief wearing glasses not enough at 7mm end

My scopes are a 10" GS Dob, 5" C5+ SCT and 8" NexStar 8GPS SCT and it=20
seems to work well with each (though providing nearly 2X the=20
magnification with the latter at 2032 mm or so focal length). Finding=20
something fuzzy and being able to zoom in to see what it is without=20
changing EPs is a real plus -- especially with a Dob where changing an=20
EP often loses the object.

Phil

Mark & Roslyn Elkington wrote:
GTO ZOOM Review
=20
In brief
=20
Spec
=20
- US$60
- 22mm-7.4mm (40-60deg AFOV)
- 1.25 inch barrel
- Just enough eye relief at 22mm for when wearing
glasses, eyecup folded down
=20
Cons
=20
- ridiculously cheap
- narrow AFOV at low mag (as with most zooms)
- not parfocal (as with most zooms)
- fussy about eye position for sharp image
- some ghosting with bright objects
- bright yellow tinge around moon
- light halo around edge of field at higher mags
- image wonky at very edge
- eye relief wearing glasses not enough at 7mm end
=20
Pros
=20
- ridiculously cheap
- lightweight and compact
- roll-down eyecup
- surprising sharpness if you hold your head right
- instant hit as =93dust cap=94 ep, ready to go
- visitors have fun playing with mag
- watch that sky darken - a contrast knob for your scope
- with non-tracking scope, zoom out to re-find object
- effortlessly try out and dial up the ideal magnification
=20
The long version
=20
I posted here a few months back asking about barlow+lenses vs lenses on=
ly ep
options, and some people suggested considering a zoom. I did the usual =
fish
around, and came up with price categories of small, medium and large (U=
S$60,
150, and 300+). They all offer very similar specs of about 7-22mm, 60-4=
0
AFOV. I find my SLR=92s 28-200mm zoom indispensable, so I figured zoomi=
ng on
the telescope was worth at least worth a look.
=20
The GTO seemed ridiculously cheap at US$60. However, it gets some
half-decent reviews (e.g. www.excelsis.com). Since I don=92t have a try=

before-you-buy option, the GTO was the cheap way to check out the whole=
zoom
concept. I ordered it from Hands On Optical (along with an Anteres 3x
barlow). Well packed and timely delivery.
=20
The lens is compact & lightweight. One reviewer commented on its cheap =
feel,
but I found it was made of metal and glass and nothing fell off :-) Mor=
e to
the point, it shouldn=92t be prejudged for not being a 1-pound hand-gre=
nade.
=20
Bad points which are standard for this category of zooms, i.e. non-parf=
ocal
(I knew this, a nuisance all the same, though I think some more pricey =
zooms
might be parfocal?), and 40deg AFOV at 22mm, which I also knew.
=20
My scope is an 8 inch f/6 Guan Sheng dob (sweet unit). The lens barely
accommodated the whole moon in at 22mm, and put a substantial yellow fr=
inge
around the lit edge. It wasn=92t there in my GS standard 25mm plossl. T=
his ep
clearly ain=92t perfect. But, twist the zoom and=85Houston, the eagle h=
as
landed! You fly down towards the surface.
=20
I took some time swapping between my GS standard 9mm plossl (Nagler? Wh=
at=92s
that?) and the zoom dialled in to an estimated 9mm (it has markings at =
7.4,
11.0 and 22mm). The moon really is an exquisite object. I got distracte=
d
just cruising around. I picked features that had both fine detail and l=
ow
contrast, and swapped back and forth between eps. The GTO seemed to be =
fussy
with eye position: sometimes it was as sharp as the plossl, other times=
a
tad off. Might have been ghosting related, though I noticed the same th=
ing
with stars. However it did seem to pretty consistently match or better =
my GS
25mm plossl on star sharpness.
=20
Images were wonky right at the edge, but pretty flat across the field, =
even
at 60deg. Mars had a little ghost running around, but no more annoying =
than
diffraction spikes. I wear glasses and there=92s just enough eye relie=
f to
catch the whole 22mm field with the eyecup rolled down. Beyond about ha=
lf
zoom, the lens gave slight glow around the outer 10%. A few times I tho=
ught
I was looking at dark nebula in the middle of the field, except it foll=
owed
me around. Annoying but livable.
=20
I=92d be interested to compare it to its upmarket counterparts, and to =
some
premium fixed eps. I started to get used to the 40deg AFOV at low mag, =
but
dopped in my 12.5mm/70deg WA for a reality check - a totally different
viewing experience. WA provides object context and a sense of immersion=
; for
me this so important aesthetically.
=20
All that said, the GTO Zoom is a keeper. It instantly became my =93dust=
cap=94
ep, sitting in the scope ready for a quick look (the scope has become a=

piece of lounge room furniture, sitting inside the sliding glass door a=
nd
ready to be lugged out on to the deck in one piece). Roz and the kids l=
ike
the zoom; it offers the casual viewer more active participation in the
observing experience through effortless tuning of magnification. Perfec=
t for
FANS 2003 (Festival of Astronomy, North Sydney) a few weeks back. One o=
f the
most striking effects is watching the sky go from grey to black as you =
zoom
in - a contrast knob on your scope.
=20
A stand-out benefit is when using a manual scope at high mag. If you lo=
se
the object (as you do), it=92s very handy to be able to zoom out, pan a=
nd
recapture, then go back in. My Mars glass is the GTO zoom + 3x Anteres
barlow, giving a mag range of 164 to 486 (should cover the most freakis=
hly
good seeing). A zoom is nice with an object like Mars: you can precisel=
y
tune the ep viewing conditions.
=20
I did a bit of DSO (galaxy) hunting, and ended up just leaving the zoom=
in
for most of the night. Partly new-toy novelty, but I was consciously wi=
lling
to trade some low mag FOV for the ability to dip in at any time for clo=
ser
look. I=92m still planning to get a premium 25mm WA; it will be interes=
ting to
see how often the zoom comes out then.
=20
Mark
=20
=20
=20

Phil,

I have the Vixen 8-24 zoom EP, and it is my workhorse. I occasionally
pop something else in at the wide end or the low end (Lanthanums), but I

do use it at least 90% of the time.

Yes, they do make you lazy like that :-)


My review of the Vixen would be similar to yours of the GTO except for
the following items:

- fussy about eye position for sharp image
- some ghosting with bright objects
- bright yellow tinge around moon
- light halo around edge of field at higher mags
- image wonky at very edge
- eye relief wearing glasses not enough at 7mm end

Near-perfect? How would you say it compares with a premium fixed lens
at a given focal length?

My scopes are a 10" GS Dob, 5" C5+ SCT and 8" NexStar 8GPS SCT and it
seems to work well with each (though providing nearly 2X the
magnification with the latter at 2032 mm or so focal length). Finding
something fuzzy and being able to zoom in to see what it is without
changing EPs is a real plus -- especially with a Dob where changing an
EP often loses the object.

Indeed.

Cheers,
Mark

Mark Elkington wrote:

Phil,



I have the Vixen 8-24 zoom EP, and it is my workhorse. I occasionally
pop something else in at the wide end or the low end (Lanthanums), but I

do use it at least 90% of the time.

........

Yes, they do make you lazy like that :-)

.........

My review of the Vixen would be similar to yours of the GTO except for
the following items:

- fussy about eye position for sharp image
- some ghosting with bright objects
- bright yellow tinge around moon
- light halo around edge of field at higher mags
- image wonky at very edge
- eye relief wearing glasses not enough at 7mm end

..........

Near-perfect?

..............

No. The GTO review also said:

- narrow AFOV at low mag (as with most zooms)
- not parfocal (as with most zooms)

And that is true of mine, too.

.............

How would you say it compares with a premium fixed lens
at a given focal length?

.............

I do not have any premium EPs, I'm afraid. My best are two Vixen
Lanthanums, 4 mm and 10 mm. I don't often get to use the 4 mm. The 10
mm is a tad better than the zoom at 10 mm. I also have an Apogee 9.5
mm; it is supposed to be good, but I've not really put it through its
paces (forgot it when I went to the desert last weekend).

The zoom is really best for what I am doing mostly now: Trolling for
faint fuzzies. I should likely be trying them on the 10 or 9.5 mm EP
with my UHC filter in place (I keep forgetting to use that, too!).

Phil

PS GTO and other zooms reviewed:

http://members.tripod.com/irwincur/gto_zoom.htm
http://www.cloudynights.com/eyepieces2/zooms.htm
http://www.cloudynights.com/eyepieces/zooms.htm

Mark