Askar FRA400 Review

 

Askar is a Chinese brand that markets a bewildering array of scopes of all sorts and sizes, but this one is especially popular, with a reputation as a good-value small imaging scope so I thought I’d review it (thanks to Richard for the loaner!)

 

Like other popular imaging scopes, The FRA400 is a Petzval (i.e. it has a built-in correcting lens to reduce the focal length and flatten the field). I’m curious how that integrated approach compares to something Tak’s FS-60 (or new FC-65D) that requires a separate flattener (or reducer) for imaging and I’ll hopefully be able to do a comparison in due course.

 

Note: I’ve restricted the example images below to just 30s due to increased white light pollution in my local area of late.

At A Glance

Telescope	Askar FRA400
Aperture	72mm
Focal Length	400mm (280mm w/reducer)
Focal Ratio	F5.6 (F3.9 w/reducer)
Length	295mm + 20mm visual back
Weight	3.2Kg incl. rings, plates

 Data from Me.

What’s in the Box?

The FRA400’s oversized shipping carton has marketing pics on the outside, like a regular consumer product! On the inside is a very thick and protective chunk of cut ethafoam that contains just the tiny OTA complete with its rings, dovetail and little accessory plate on top.

 

 

 

Design and Build

This type of small quintuplet imaging scope made in China has proliferated in recent years and some aspects (focuser type, ring style, colourful anodising) will be familiar across many scopes and brands. That’s because ‘Askar’ is (I believe) just one marketing brand of Kunming United Optics. The question then is whether you can cross-shop on price with their other brands that produce similar scopes, or whether there are subtle differences in materials, specs or (especially) quality? I just don’t know.

 

Optics

The FRA400 employs an optical configuration known as a Petzval that contains a second lens group within the OTA. This was originally found in camera lenses and was re-discovered by Al Nagler of TeleVue for use in scopes. There’s a lot to discuss here, so this will be a long section – just skip it if you’re not interested!

 

So what is a Petzval anyway?

 

A Petzval is a compact, highly-corrected, short focal-length refractor. It achieves this by combining a long focal length objective with a smaller Petzval lens group in front of the focuser that acts as a reducer/flattener. The Petzval lens group corrects many of the aberrations inherent in the objective, and halves the focal length (so an F5.6 Petzval will have an objective operating at ~F11). It reduces the physical length of the OTA as well. However, the Petzval lens only corrects monochromatic aberrations, like off-axis astigmatism and coma. It doesn’t correct for chromatic aberrations - false colour and spherochromatism, the variation of spherical aberration across wavelengths - which are (mostly) determined by the objective.

 

Many Petzvals – e.g. TeleVue’s NP-101 and Takahashi’s FSQ-106 – have a four element configuration with a doublet objective operating at ~F11 and a doublet Petzval lens. This isn’t the only way to do it. For example, Vixen’s current AX103 imaging refractor has a triplet objective and a single Petzval element (likely only acting as a flattener, not a reducer). Meanwhile, Vixen’s VSD70SS and VSD90SS imaging scopes have a doublet objective and a triplet Petzval group (all with huge air gaps – great for correction but problematic in terms of de-centring).

 

The Askar FRA400 also boasts five elements. So it’s the same as the Vixen VSDs then? No! The FRA400 seems to have an ED triplet objective with a doublet Petzval lens (also with an ED element). Both the objective and Petzval groups have either tiny air gaps between the elements or they’re cemented. There is no sign of foil spacers (good news for star images), but I think I can see a ring spacer in the objective, so this is likely a conventional air-spaced triplet with a central ED element.

 

Now let’s unpack all that. An ED triplet objective (72mm operating at ~F11!) will give the scope outstanding false colour correction at this aperture. Small air gaps are simpler and more robust, less likely to suffer from de-centring (a real problem btw). However, they offer less options for correcting aberrations, so we might expect less perfect correction than say a VSD because Petzvals suffer two main optical limitations/issues:

1)    Vignetting, unless the rear group is of large aperture

2)    Off-axis astigmatism

The FRA400’s rear Petzval lens group is oversized at ~57mm and with a clear aperture of ~55mm, so vignetting shouldn’t be a problem and Askar claim a 44mm image circle (i.e. good for full frame sensors). Askar sell a reducer for the FRA400, but it’s interesting that it apparently doesn’t need a flattener for full frame, unlike Takahashi’s FSQ-85.

 

The only other thing to note is that all elements appear coated and the external ones at least are of high quality.

Laser confirms objective is a regular triplet with no large air gaps.

 

The Petzval group, seen through the objective.

Large diameter Petzval lens group seen through the focuser drawtube (visual back unthreaded).

Tube

The OTA is very short. From the front of the metal push-fit dew-cap to the M68 male thread on the back of the draw-tube measures 295mm, but add another 20mm for the 2” visual back that threads onto it. The short dewshield slides on a felt bushing – action is firm so a tension screw isn’t needed. Small it may be, but the hefty focuser and all that glass make the FRA400 heavy at 3.2Kg including the rings and plates.

 

External finish is the kind of pebble powder coat used by Tele Vue and typically more chip-resistant than gloss paint. The entire OTA and focuser are baffled internally with machined-in micro ridge baffles, as well as flat black-painted. The lens ring and accessories are red anodised, but this appears to fade. Otherwise, quality appears very high.

Focuser

The focuser is a hefty CNC-made unit, with a broad cross-cut rack and a 3” (76mm) diameter drawtube with 55mm travel. Like a Feather Touch, it has an inner fine-focus wheel (gold here, red on some). The fine-focus action is smooth and precise, if not quite up to Feather Touch standards. The coarse knob is a little granular and stiff feeling.

 

There is a lock knob on the pinion and the focus tube, but the latter doesn’t feel very strong or progressive. The end of the drawtube incorporates a camera-angle adjuster (rotator). It doesn’t rotate the focuser body, so the knobs stay in the same position. Its action is smooth, but it doesn’t lock very solidly.

 

Another minor demerit is the lack of any threads on the visual back – you’re stuck with a 2” nose piece by default. The 2” eyepiece holder does have a compression ring with three screws for secure fastening, but I’d prefer a way of using a threaded camera mount for better orthogonality (there’s no tilt adjustment either).

 

The whole visual back threads off the focuser tube to expose male M68/female M64 (I think) threads onto which the reducer attaches. But you’d need to get creative with adapters (ironically, probably from Borg) to fit a camera mount without the reducer.

 

It’s interesting to compare this focuser with the ‘old-fashioned’ cast unit fitted to the latest small Takahashi imaging refractors – the FC76DP, FS-60CP and FCT-65D. On paper the FRA400’s is better, with its CNC construction, fine-focus wheel and big drawtube with scale. But in some ways – smoothness and precision, the secure progressive action of the draw-tube lock and connectivity options too – I actually prefer the Takahashi.

 

Mounting

The FRA400 is short but fairly heavy for its size. It should go on most small equatorial mounts or a medium alt-az for visual with the included split CNC rings and Vixen-compatible plate. One minor issue is that to adjust/balance the tube position means slackening off a pair of Allen bolts, but the tube is so short there’s not much room for adjustment anyway.

Accessories

The FRA400 ships with split CNC rings, a little Vixen-compatible dovetail plate and a small female dovetail on top intended for attachment of a guide-scope but that you’ll use as a handle. There’s no finder and for visual you don’t absolutely need one at the this focal length, but for imaging it’s handy because of the need to refocus between eyepiece and camera.

 

Askar sell a 0.7x reducer for the FRA400 that brings the focal ratio down to an ultra-fast 280mm/F3.9 with an image circle of 44mm (full frame). It achieves this with three widely separated elements ~55mm in diameter. All glass surfaces seem very well coated. It’s a nicely made piece of kit mechanically, too, with thread-on metal covers.

 

The reducer threads into the focuser draw-tube in place of the whole visual back, via an M68 (I think) thread concealed in the reducer’s flange. This means the reducer sits inside the focuser draw-tube (making for a neat and compact combo).

 

On the camera side, the reducer connects with a standard M48 male thread to fit a wide-T adapter from the likes of Baader.

 

 

 

Reducer body fits inside focuser drawtube for a compact arrangement, ends in an M48 thread to reduce vignetting.

In Use – Daytime

My usual test of branches in silhouette against a bright cloudy sky at ~100x (actually 108x with a 3.7mm Ethos) yields almost no false colour, even focusing through, and a commendably sharp view. This is super-APO performance. The view of a Magpie sitting on top of a pine tree 100m from my window, at a 16x spotting-scope magnification with a 25mm Plössl, is superb – ultra sharp and bright with no false colour at all.

 

The FRA400 is happy to focus close, too. At perhaps just 20m, views into trees in autumn leaves at 32x with a Nikon NAV 12.5mm are stunningly bright, sharp and immersive, the field stop vanishing into peripheral vision.

 

Perhaps surprisingly (it’s an astrograph), the FRA400 would make a marvellous little field scope. Too bad few birders will ever find out.

In Use – Astrophotography (400mm/F5.6)

The FRA400 needs a short extension to come to focus natively (but not with the reducer/flattener). For connection to my DSLR, I used a Baader Protective Wide-T camera adapter which has a nosepiece fitted to a 52mm bayonet. I then found live-view focusing very easy: an advantage of imaging with a small APO is that perfect focus is easy to find.

 

A frame of the starfield around M33 shows excellent coverage and correction. Star images are good off axis, with just a tiny amount of distortion in the very corners, probably due to astigmatism, but I’m being very fussy here. There is very little vignetting. Bloating on O-A stars seems well controlled (see also crop of Pleaides below). Even though I was using a nosepiece not a threaded connection, there is little evidence of tilt (those triple set-screws work well.

 

You wouldn’t choose the FRA400 for imaging the Moon, but the snap I took with the FRA400 is very good for just 400mm FL: more evidence of the strong optical quality.

 

Minor imaging issues included the weak locks on the drawtube and rotator. A more significant one was the short dew-shield. Actual dewing might be a problem, but the more immediate one is stray light: unless you’re working in very dark ambient conditions (as opposed to the overall light pollution level), you’ll get stray light fogging your images. To fix this I knocked up a long extension from card and secured it with a cable tie, but a better solution would be an extension from the likes of Kendrick.

 

Overall, the FRA400 should produces excellent images, even without the reducer.

 

Single unprocessed (hot pixel crosses and all!) frame of M33, Askar FRA400 F5.6 with Canon EOS 6D MkII: 30s, ISO 3200.

 

Bottom left corner crop of same image.

Single unprocessed crop of M45, Askar FRA400 F5.6 with Canon EOS 6D MkII: 30s, ISO 3200.

 

Despite small image scale, FRA400 takes a very decent snap of the Moon.

In Use – Astrophotography (280mm/F3.9)

An adapter ring on the back of the 0.7x reducer threads onto the focuser to give a secure and orthogonal connection. On the camera side, it ends in an M48 thread to which I attached the Baader Protective Wide-T again, but this time using its M48 insert (if you’ve got one of these, you need to unscrew the M42 collar from the insert first).

 

Again, focusing was easy and the results good, with very minor distortion of stars in the corners. The FRA400/Reducer captures a giant area of sky at just 280mm FL, enough to frame even the largest DSOs. However, some vignetting is now evident at the corners and edges too. I didn’t see any evidence of an increase in chromatic aberrations, but I did note some spikes on brighter stars that weren’t there natively, not sure why.

 

I was slightly disappointed by the reducer, especially compared to the excellent native optics.

 

Single unprocessed frame of M31, Askar FRA400 at F3.8 with Canon EOS 6D MkII: 30s, ISO 3200.

 

Bottom left corner crop of same image.

 

In Use – Observing the Night Sky

General Observing Notes

The focuser a little less oily smooth than the best, but precise and with little image shift except above 100x. The rotator is useful visually, but it suddenly gave way and would have dumped a (very) expensive eyepiece if it hadn’t been securely tightened into the diagonal.

 

It’s not really possible to balance the short OTA with the rings (just as well since they need an Allen key). Instead, you have to (try to) adjust the plate in the dovetail to balance different focuser loads.

 

The very short tube also makes eyeball sighting harder – a finder would be useful. The dew-shield is too short when working around streetlamps and allows some veiling flare but is more of a problem for imaging (see above).

 

The field is not perfectly corrected with simple eyepieces (see note below) and eyepieces with built-in extenders (Naglers, Ethos, Delos, etc) work better for extended DSOs.

Cool Down

Cooldown wouldn’t be a thing with a 72mm doublet, but this is a quintuplet and a Petzval (so it entrains air between the objective and rear elements). Consequently, I saw tube currents for the first hour from a warm house: initially Jupiter looked mushy and lacked contrast.

Star Test

Once fully cooled, the star test is virtually perfect with identical rings either side of focus and a good in-focus star image.

The Moon

The FRA400 gave a very sharp and detailed image of a 13-day Moon at 114x with a 3.5mm Nagler. From the Aristarchus plateau, through Gassendi with a hint of its craterlets and rilles, a portion of nearby Sirsalis rille and dark-floored Billy, there was lots to explore. Focusing through the limb I detected just a hint of gold false colour. Comparison with an FC-60 suggested a little more detail, but a marginally less contrast and a warmer tone.

Jupiter

At 108x with an Ethos 3.7mm, Jupiter was an outstanding view for a 72mm scope when fully cooled. The planet was perfectly focused with no stray light or softness and extreme focus snap from the steep light cone: a really beautiful view.

 

I noticed definite changes in thickness and density in the NEB and SEB and the grey polar hoods. Then I spotted a tiny black dot near the centre of the disk. I checked and sure enough – I’d caught a shadow transit of Io.

Mars

Mars at just 12” across, early in the 2024-25 opposition, was peeking over the roof of the house opposite and I quickly got it in the 3.7mm Ethos at 108x before the clouds rolled over.

 

When low down, Mars often boils red light into the seeing with objectives that aren’t perfectly corrected in the red (most ED doublets), but not here. Thank an ED triplet operating at ~F11 (LZOS’ best planetary refractor is a 130mm ED triplet of similar design operating at F9, so you get the idea!)

 

The FRA400 delivered a perfect gibbous Mars, with a strong red-orange colour and crisp focus. I could make out a lighter spot at the pole and hints of darker albedo markings.

Deep Sky

The Pleiades through a 25mm Plössl looked good, but I noticed astigmatic star images in the outer 25% or so of the field. Upping the power with a 12.5mm Nikon Nav cured all but a trace of astigmatism near the field stope to deliver a beautiful and immersive view. (A quick note on the NAV: those extra 10 degrees over an Ethos 13mm really make the field stop disappear to leave me hanging in space – amazing!)

 

The NAV gave a similarly excellent view of the Orion Nebula. Whilst in the area, I thought I’d try splitting Rigel, a tough target for this aperture. But I managed to spot the dim companion wobbling at the edge of the outer diffraction ring at 108x with the Ethos.

 

Castor was a very easy split at medium powers.

Summary

The FRA400 is primarily an astrograph. As such it’s excellent. I was particularly impressed with the results natively. The oversized Petzval group keeps vignetting and astigmatism under tight control out to the edges of a full frame and the ED triplet controls chromatic aberrations well. The absence of spacers in the objective means cleaner star images too.

 

I was slightly less impressed with the reducer, which still offers a well corrected field and doesn’t add false colour or bloating, but does vignette at the edges of a full frame. If you want something very fast for full frame at modest cost you might be better with the likes of Tak’s FC-65CP with its super reducer.

 

Oddly (for an astrograph) the FRA400 also works very well for visual! False colour is almost non-existent and views of Mars suggest very low sphero-chromatism. Askar have paid attention to high optical quality and alignment too, so the image is sharp and detailed with textbook star images at high magnifications – something most astrographs don’t do (or require extenders to achieve).

 

The choice to avoid large air gaps seems to me very wise. I’ve seen too many scopes with de-centring problems recently. The trade-off, compared to say a Vixen VSD, seems small, at least natively.

 

The few negative points all relate to the standard Chinese hardware. The focus action is ok, but a bit stickier and more granular than the best. The focuser lock knob is barely adequate and there is no obvious way to thread on a camera adapter without the reducer. The rings are only adjustable with an Allen key (why?) One other thing to note is the slow cooldown time: I wouldn’t recommend the FRA400 for quick looks (or images) despite its tiny size. But these are all minor gripes.

 

The FRA400 is a wonderful little imager, which also does surprisingly well as a super-compact visual scope. Highly recommended, but be aware of the long cooldown time if you only have short periods to observe/image.

 

 

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