Astro-Physics
92mm Stowaway Review
Anyone who’s read my refractor reviews
will probably know that I’ve been moaning about not being able to get hold of a
Stowaway for many years.
I’ve always regarded the 90mm class as
the ideal travel scope, for my needs at least, so obviously I wanted what was
likely the best of breed. Unfortunately they’ve been waitlisted and unavailable
forever.
Personally, I’d been on an AP waiting list for almost
twenty years... but it was the wrong one (back then I’d wanted a big refractor,
a 155 or 160). Could I swap list? Err... no, sorry.
Then, most unexpectedly, I received an email from Marj at AP
on the 23rd July 2021, saying they were opening a brand-new list on
July 30th to close just a week later. But the surprising thing was
that, instead of a queue, the new list was to be a random draw.
Long story short, I got one. If you’re interested in the
order process, I’ve documented it here. Now we just need to find out if the
legendary AP Stowaway really lives up to its reputation...
At
A Glance
|
Telescope |
Astro-Physics
Stowaway 2021 model |
|
Aperture |
92mm |
|
Focal
Length |
612mm |
|
Focal
Ratio |
F6.65 |
|
Length |
19.5” (495mm) |
|
Weight |
3.6 Kg incl rings, no dovetail |
Data from AP.
What’s
in the Box?
Since I’m highly
unlikely ever to buy another new AP scope (or even get the chance to), I’ve
included a full set of unboxing pics:
The Stowaway
arrived just in time for Christmas!
The Stowaway
is quite lavishly spec’d for such a premium product. Everything you see was
bundled for free, including that Peli case with custom dividers, super-thin CNC rings and an
AP Vixen dovetail plate; all the visual back adapters too. Only the handle you see in some photos was an
after-market accessory. This goes a long way towards justifying the price.
Kudos to AP here – they could charge more.
Design
and Build
AP
scopes have a unique look and build that stretches back to my thirty-year-old
130 EDT, even though recent models are a bit more sophisticated. But that look
helps brand identity and TeleVue have long adopted a
similar approach.
So
this 3rd generation Stowaway looks much the same as the 2nd
but in detail it’s different. It now has an air-spaced objective with the same
aperture (92mm) but a slightly longer focal length. Consequently, though
slightly larger than the original, it’s still almost identical in size and
weight to a TV-85, itself a very compact scope.
AP
has given in, like TEC before them, to using a 2.5” Starlight FeatherTouch focuser in place of their own. It reduces the
distinct AP character a bit, but it’s the perfect focuser for the multi-purpose
photo-visual role the Stowaway aims to fill.
Attention
to detail is the usual AP near-obsessive, with clever features to make it
light, easy to use and deliver the very highest contrast. Build quality is of
the highest.
Optics
The Stowaway
has a typical ED triplet with the soft centre crown element made of high-end
FPL-53 (fairly common these days), sandwiched between two hard flints. It’s an
arrangement that offers very high correction at this aperture and focal length,
along with protection from dew and wiping. As usual with triplets, cool-down
will be a bit longer and the objective a bit heavier, but at this size not
significantly so (by 7” aperture, triplets become very heavy and slow cooling).
AP claim
that the objective maintains a minimum of 90% Strehl
across the whole visual spectrum, so spherochromatism that can soften the view
of Mars and bloats O-A stars in images shouldn’t be a problem.
My old 130
EDT has an air-spaced objective, but many recent AP refractors are oil-spaced.
Enough to say that whilst oil-spaced has some advantages, it allows for less
freedom in selecting curves and so potentially a relatively lower level of
correction. Then there’s the possibility of leaks and that it may need
horizontal storage to deliver it’s best. Overall, I reckon the decision to go
air-spaced is the right one, even if these days the more conventional too.
Given that
the similar 90mm/600mm Chinese triplet has an excellent reputation, you might
ask what extra you’re getting from AP? The answer is basically that the normal
distribution for optical quality – including, but not only, Strehl
- will be much narrower for the AP.
The more
complete answer will point out that AP is very fussy over the quality of glass
blanks it uses and reputedly rejects a lot due to too much inhomogeneity,
striae, bubbles etc. It will also mention more careful polishing, mounting and
collimation and, perhaps, better coatings too. All that is surprisingly
expensive to deliver.
Yes, but can
you see the difference between this and a similar, cheaper lens? I believe so,
but the differences are subtle and often only apparent in fine seeing at high
power. Also, when combined with the custom flattener this objective promises
pinpoint, bloat-free stars to the edge of a 50mm image circle.
Tube
The tube is
a beautifully made thing, with a powder coat that’s more subtly textured than a
Tele Vue. Quality feels even higher than a TV-85’s, if in a less heavy-weight
way.
The sliding
dew-shield, finished with a micro-baffled and anodised end-ring and flocking,
has a perfectly weighted action and a stainless lock-screw with AP’s signature
knurling.
Internally,
the Stowaway has multiple knife-edge baffles, rather than the usual two or
three, for supreme suppression of stray light and the highest contrast.
Focuser
As I
mentioned before, this 3rd generation Stowaway has dropped the
classic AP focuser for a dual-speed 2.5”
Starlight FeatherTouch rack-and-pinion with a rotator
and a special visual back. It’s sufficiently heavy duty for bigger cameras or
Bino’s, but doesn’t add too much weight.
If
you’re familiar with FeatherTouch focusers, you’ll
know that manual focusers don’t come any better, which is why they’ve slowly
taken over at the high end. Smooth, super-precise and stable, with a lovely
feel and build.
The
visual back is unique and has a full-aperture (i.e. 2.5”) circular dovetail with
three thumbscrews called ‘DoveLoc’ to take AP’s flattener
or reducer (see accessories section), in addition to the usual 2” and 1.25”
eyepiece holders. This feature should support the largest sensors (AP always
made a point of being medium-format friendly back in the days of emulsion).
The
Stowaway came with the first adapter (from the full DoveLoc
to 2”) held in with thumb screws, but they also supply replacement hex grub
screws if you’re not going to be using it much (see images). Why? So you don’t
loosen the wrong ones in the dark – more of that obsessive attention to detail.
FTs
may be fitted to other scopes, but given the AP branding and custom visual back
components, this FeatherTouch is still a unique
variant. Adopting it over their own was a doubtless a difficult decision for
AP, but the right one - to me the focuser just feels perfect for the job, ‘nuff said.
AP
warn that the focuser isn’t up to the very largest and heaviest cameras, unlike
the 3.5” focuser on the 110 and 130 GTX models.
Mounting
The Stowaway
comes with a set of rings and a Vixen dovetail plate. You can buy other
dovetails to fit the rings, including Losmandy-D
pattern, for larger mounts. The rings aren’t hinged, but they easily
disassemble and do make it very easy and safe to slide the tube around for
balance.
The
Stowaway’s small size and light weight mean it’s OK for visual on a small
mount, like the Vixen Porta shown; but something a bit more solid would work
better for higher powers. You’d need a medium mount for imaging and I found the
Stowaway very stable on my Vixen SX2.
Accessories
The Peli 1525 case is a standard item that AP has customized with
the expensive TrekPak insert to fit the Stowaway, but
the dividers can be moved about to suit your own needs. Spare dividers and
retaining hasps are provided. The case is light for a Peli
and it’s carry-on sized.
The
super-thin CNC rings are made in-house and the Vixen-fit dovetail plate is likewise
an AP item. These are of the highest quality and as light as they can be.
If you want
to fit a finder, you’ll need to fit it via a mini dovetail plate you can buy
for the top of the rings. Numerous other accessories are available, including a
reducer. The only one I’ve bought so far is the handle, which fits atop the
rings and helps handle the tube safely.
For imaging,
Astro Physics offer two options:
1) A custom 1.0x flattener – Part 92FF - with an image
circle of 50mm (!) that’s colour corrected deep into the violet for modern CMOS
chips
2) A 0.8x reducer/flattener – Part 92TCC - to reduce
the focal length to 488mm (F5.3) with an image circle of 40mm
These fit
into the circular dovetail called ‘DoveLoc’ that’s incorporated
into the focuser and should pull the reducer/flattener into perfect alignment.
AP make a
wide camera adapter with a 47.6mm bayonet to fit either of these, parts
DSLR25EOS for Canon or DSLR25NIK for (you guessed) Nikon.
In
Use – Daytime
Of course,
it’s not waterproof, but the Stowaway is just small enough to use for birding
or nature viewing in fine weather or from a hide – it delivers sharp and
aberration-free high-power views that no spotting scope can match. Even
focusing through silhouetted branches at 100x yields no false colour.
The Stowaway
turns out to be an excellent full-frame terrestrial telephoto lens, even
without a flattener – super sharp centre field, aberration free and with
minimal vignetting using a wide-T.
I used a
short AP extension tube to get focus (superbly baffled like the OTA and
focuser).
Full-frame
snaps through the Stowaway – Canon EOS 6D MkII w/ Baader wide-T. Straight from the camera.
Crop from
another snap – no other processing.
In
Use – Astrophotography
I used a Baader wide-T mount to allow the maximum coverage on a full
frame sensor. Sure enough, coverage is excellent and vignetting very modest at
full frame. There’s quite a bit of off-axis field curvature (and some tilt here
- my bad), so as you’d expect you would need a flattener for wide-field imaging
with the Stowaway. Violet bloating on bright O-A stars is well controlled.
AP offer
their own reducer and flattener for the Stowaway and the custom flattener looks
especially impressive (see accessories section). I’ll update this section if I
get the chance to try them.
The Stowaway
produces quite detailed lunar images, given the small image scale. The one
below was limited by seeing and I’ll update it in due course.
M42: 15s ISO
4000 Canon EOS 6D Mk II (single frame, unprocessed).
Unprocessed
crop of the Moon with EOS 6D Mk II.
In
Use – Observing the Night Sky
General
Observing Notes
The Stowaway
is just really easy to use. The small size and low weight make it simple to
mount up and the accessory handle helps too. It cools fast (see below); focus
snap is superb; all aberrations are low. The focuser is highly stable and
precise, for imaging or visual use and there’s ample travel.
Cool
Down
Triplets,
even small ones, can take a long time to cool. Not the Stowaway. Even from a
warm house into a frosty night, it was usable almost immediately and giving
perfect views within 20 minutes. This is a really great feature for this type
of scope and suggests thoughtful cell design.
Star
Test
The star
test is excellent, but confirms what we know – Roland hand finishes and tests
every optic to very high standards.
The
Moon
The Stowaway
delivers the Moon as perfectly as any 90mm aperture could, with a surprising
level of detail on stable nights and all with the highest contrast and no trace
of false colour wash or fringing, even focusing through the bright limb.
Very low
flare means mountains silhouetted against space on that limb are placed in
stark contrast with velvet black around, again a result of the highest optical
quality.
Planets
The Stowaway
gave me some of the finest planetary views I’ve had with any 4”-class
apochromat. On a freezing but very stable night up on the fell before
Christmas, its prowess was almost immediately obvious, even to my wife who
commented on it unprompted. So sharp, so crisp and full of contrast.
Venus
Crescent
Venus looked the way it rarely does in any scope – absolutely crisp and
dazzling at 153x with a Nagler zoom at 4mm, with no false colour, flare or
light bleed. Ashen light? Check. Slight indentations in the terminator? I think
so. Wow.
Mars
The Red
Planet troubles F6 ED doublets like the TV-85 with red blur and softness. Not
the Stowaway. There was no blur of deep red false colour, in or out of focus. With Mars at 16.9” near the 2022 opposition,
near transit at 57° Altitude in fine seeing, at 153x with the 4mm setting of a Nagler Zoom, it
even remained sharp at 204x with the 3mm in steady moments.
Mars
was showing its classic ‘bikini’ of Syrtis Major just off centre extending into the lighter equatorial regions of Arabia to the
north and bright orange Hellas with its
clearly defined arc of northern boundary to the south-west. To the west, I noted the twin ‘bikini straps’ of dark albedo – Sabaeus Sinus and Mare Sarpentis
according to my atlas – leading to the prominent dark area of Meridiani Sinus
on the limb.
As a point
of reference, the TMB 115 showed just a little more contrast and detail on the
night, but much the same view.
Jupiter
Jupiter at a moderate 37” across just showed so much more subtly shaded
detail than I’m used to at this kind of aperture and completely sharp with
extraordinary contrast for such a small scope. Masses of subtle shading and
fine banding in the polar regions; the obviously pink north equatorial belt
with hints of pale storms and changes in thickness and density. I was surprised
too to perceive clear differences in the colour and brightness of the Galilean
moons, with Ganymede a noticeably greyer hue than Io.
Upping the magnification caused no softening of the view at all and it
would have taken lots more than 153x, the most the Vixen Porta mount would
allow.
Saturn
Saturn at 15” across showed a perfectly crisp ‘mini-Cassini’ view
etched into black space that I love and with all the main features visible: the
Cassini division, ring shadow and polar hood, hints of belts. Again, that
creamy colour was beautifully picked out.
Deep
Sky
92mm
aperture is small for deep sky, but the combination of peerless contrast and a
big field of view make it a lot of fun for clusters and bright nebulae. I had a
most enjoyable evening with it early in the New Year, viewing out over the bay
from a secluded and dark spot on the Prom’, mostly using a 19mm Panoptic
eyepiece giving 32x magnification.
The Great
Nebula in Orion revealed a lot of structure in the inner region that I expect
from apertures above 4”. I easily picked the oval misty patch of the Crab
Nebula out of the darkness above Zeta Tauri too.
This is a
great size scope for open clusters. The Pleiades were glitteringly brilliant
blue, sparkling in their misty nebulosity with a hint of structure around
Merope – beautiful! The Beehive was similarly a wonderful view – with the whole
cluster easily encompassed by the two-degree field.
The Starfish
in Auriga showed its sweeping arms of stars more clearly than I recall in a
scope of this aperture, whilst the Double Cluster was impressively bright and
well populated too.
The Owl
Cluster in Cassiopea was my favourite view of the
night. It’s spookily brilliant eyes really glowed out of the darkness and its
outstretched wings and splayed feet much more obvious than through smaller
apertures.
Summary
You probably
won’t be surprised if I tell you the Stowaway is one of the most perfect
telescopes I have tested and one of the most useful. Put the finest optics and
focuser in a superbly baffled and lightweight tube, add in a clever visual back
and beautifully made rings and place the lot in a thoughtfully modified Peli and you have a compelling combination. Then there’s
AP’s quality and customer service, which in my experience are second to none.
An aperture
of about 90mm is the sweet spot for travel scopes, so the Stowaway is good for
everything: wide field imaging of course, but for visual use on the Moon and
planets too (something smaller or less perfect scopes struggle with). And it
works fine on anything this side of a photo tripod, cools fast and is
super-easy to travel with in a way very few larger apochromats are, even my
favourite full-4” (100mm) ones.
So the
Stowaway is the perfect small scope then? Well not quite, because there’s the
availability problem.
I once wrote
“just buy a TV-85” in response to the Stowaway’s lack of availability and I
stand by that. Yes, the Stowaway is unquestionably better than the TV-85 in
almost every way and that adds up to a significantly more desirable scope
overall, compellingly so for some use cases. But that’s no help if you
can’t get one. And I’m using mine more carefully and sparingly than I might
because it’s unreplaceable.
The Stowaway is basically perfect: so
good and so useful that everyone in this hobby should have one. It gets my
highest recommendation... if you can afford and obtain one.
