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 saying they were opening a brand-new list 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

 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 3^rd generation Stowaway looks much the same as the 2^nd 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 slightly shorter and just half a kilo heavier than a TV-85, itself a very compact scope (see comparison pics below).

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 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 3^rd 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. For visual use I actually prefer their smaller Crayford units, which are even smoother (but are less controllable with heavy cameras).

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 or Vixen AP (!) mounts.

Stowaway on Vixen AP mount (taken on an iPhone, I’ll replace with a proper one eventually).

AP Stowaway and Tele Vue TV-85 on Vixen Porta for comparison (both dew shields extended): Stowaway is slightly shorter with the dew shield retracted but 0.5 Kg heavier.

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:

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

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. It gave great views and images of the 2022 Mars occultation.

M42: 15s ISO 4000 Canon EOS 6D Mk II (single frame, unprocessed).

Mars approaches the Moon before occultation on 08/12/2022.

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. The dew shield slides just easily enough and the dew cap is a snug fit that won’t fall off but is easy to remove.

It cools fast (see below); focus snap is superb; all aberrations are low.

The focuser is highly stable and precise, for imaging or visual and there’s ample travel. The rotator works well with little image shift.

Now you see the point of those hinge-less rings: you can progressively loosen them on one side to move the OTA for balance without fear of it popping out.

I don’t feel the need for a finder at this focal length – just use a wider-field eyepiece.

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

At 165x with a 3.7mm Tele Vue Ethos, a 12 day Moon in stable seeing is a wealth of detail to explore. The Ethos is sharp to the edge and the whole terminator from Plato to Schiller is in the field.

(Can’t afford that SpaceX tourist Moon mission? A fine refractor and an Ethos is the closest to that experience you’ll ever get.)

Highlights include the Gruithuisen domes, the banded walls of Aristarchus and nearby Vallis Schroteri, lots of interesting craters in the south, including elongated Schiller, dark-floored Billy and Gassendi with several craterlets and a rille on view.

It’s a great view, with 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 showed 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.

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