The astrograph Askar FRA600 is an apochromatic refractor with 108 mm aperture and 600 mm focal length (f/5.6). This Petzval quintuplet integrates a front triplet and a rear doublet (including 2 ED lenses), ensuring a flat field of 66 mm in diameter with no additional corrector. The FRA600 features a sturdy 4.2" Crayford rack-and-pinion eyepiece holder with 1:10 focus reduction, designed to support heavy equipment without slipping. Its construction is meticulous, with a 125 mm-diameter tube equipped with a retractable mist guard, two red anodized collars linked by a multifunction handle, and a 300 mm dovetail in Losmandy format.

The apochromatic telescope SQA106 (marketed under the Askar brand) is an apochromatic astrograph with an aperture of 106 mm and a focal length of 509 mm, i.e. f/4.8. It also adopts a Petzval 5-lens design (2 glass elements SD very low dispersion) to provide a wide image circle of 55 mm corrected, covering full-format and even medium-format sensors . The stars remain fine and punctual over the entire field (RMS spot size <2.2 µm at the corner of the 24×36 format) thanks to this optimized design. The SQA106's gray tube incorporates a lightened one-piece collar/handle with multiple screw threads for accessories, as well as a 2.8" (≈71 mm) Crayford eyepiece holder with 30 mm of travel and a 360° rotator graduated for framing . A set of rear adapters (M68, M54, M48) is supplied for easy connection to any type of camera.

Mechanical details: weight, dimensions and equipment

Both instruments feature a high level of finish, suitable for demanding astrophotography. The table below summarizes their main mechanical characteristics:

Weight and dimensions : The FRA600 weighs approximately 6.5 kg with clamps and dovetail (tube only ~5 kg). It measures 493 mm with mist guard retracted, ensuring good portability for a 108 mm instrument. The SQA106 is a hair lighter (tube ~5.8 kg) thanks to its lightened single collar, but once fitted with its Losmandy tail and accessories it reaches ~8 kg . Its tube is a little longer (516 mm folded, 586 mm with mist-shield extended). In both cases, a robust equatorial mount is required due to the weight (~7-8 kg in imaging configuration).

Eyepiece holder and mechanical compatibility : Askar FRA600 features a large eyepiece holder 4.2 inches with 1:10 micrometric dial. This large-diameter focuser offers excellent rigidity and can support heavy imaging configurations (full-frame cameras, filter wheel, etc.) without flexing. The SQA106 features a slightly smaller eyepiece holder (2,8″(i.e. ~71 mm), which is also rack-and-pinion geared. It offers 30 mm of travel and is compatible with of the market. Each bezel incorporates a field rotator This graduated rotator allows the camera to be rotated through 360° for framing without losing focus. On the FRA600, the rotator is part of the tube (M90 thread); on the SQA106, it is also included and fitted with an angular scale.

Both instruments come with threaded adapters for easy connection of various accessories. The FRA600 offers an M90×1 (rotator) thread that can be reduced via tapered adapters to M68, M54 or M48 - in addition, eyepiece holders with 2″ and 1.25″ threads are supplied for visual use or with barrel cameras. The SQA106 directly offers M68, M54 and M48 outputs (with adapters included) , covering most photo fittings (APN, astro cameras, etc.). In both cases, no backfocus ring required All you have to do is insert the camera and focus, since the field of view is already flat and the optics wide enough to accommodate the equipment.

Clamps and fasteners : The Askar FRA600 is equipped with two necklaces sturdy, red-anodized aluminum, connected by a multifunctional top handle. This handle (also painted red) features several tapped holes (M6, M4) on the top and sides for attaching accessories (finder, guide bezel, etc.) . The SQA106 takes a different approach: it has a one-piece tubular collar This unique collar is open-worked to reduce weight. This unique collar is open-worked to reduce weight and also incorporates side screw threads (M4/M6) for attaching accessories, as well as a top handle with finder base. Both scopes are supplied with a 300 mm Losmandy dovetail (~11.8″ long) ensuring stable attachment to the equatorial mount . The SQA106 also comes with a quilted Oxford fabric carrying case to protect the tube.

Internal construction quality : The inside of both tubes is matt and fitted with baffles to suppress stray reflections. The SQA106 in particular uses a matt black paintwork and optimized light-cutting rings to eliminate diffuse light and internal reflections. On the FRA600, an independent test revealed the presence of a very slight arc ("rainbow") reflection in imaging when an extremely bright star (Sirius) is in the field. This phenomenon, although weak and rare, indicates the reverberation of a bright internal surface. In normal use, most users will not encounter this problem (very specific conditions are required), and no noticeable halo or ghost image appears on bright stars with the FRA600, even with the reducer . Nevertheless, the internal anti-reflective coating on the SQA106 can be considered slightly superior, which has not reported any such reflections in feedback to date. Overall, the mechanical quality of both tubes is judged by the community to be excellent, in keeping with the high-end positioning of these astrographs.

Optical details: aperture, focal length, design and coating

Optically, both instruments are astrographs with flat field incorporating an internal field corrector. They share a Petzval-type design, with 5 elements divided into two main groups (front focusing group and rear flattener group). The following table compares their main optical specifications:

Aperture and field : The Askar FRA600 is an instrument for 108 mm diameter, slightly larger than the 106 mm of the SQA106. In practice, this 2mm difference is negligible in terms of light collection (less than 4% difference in collecting surface). The FRA600 offers a native focal length of 600 mm (f/5.6), while the SQA106 is shorter, 509 mm (f/4,8) . The SQA106 is therefore approximately 1 IL brighter than the native FRA600 (f/4.8 vs. f/5.6), enabling ~1.36× shorter exposure times for the same signal. On the other hand, the FRA600 initially covers a slightly narrower field at equal sampling (600 mm focal length corresponds to ~4.7° on the long side of a full-frame sensor, vs. ~5.5° for 509 mm).

Optical design and ED/SD glass : Both glasses use a apochromatic quintuplet. The FRA600 consists of a front triplet and a rear doublet field corrector, two of which are made of low-dispersion ED glass. The SQA106 also features 5 elements (air-spaced system), with two glass lenses SD (Super Low Dispersion) glass with very high chromatic correction. This choice of SD glass (similar to the FPL-53) on the SQA106 is designed to minimize the effect of the lens.chromatic aberration residual. In fact, the manufacturer claims near-perfect apochromatic correction: even bright stars show virtually no colored fringing on the SQA106, even in the corners of the field. The FRA600 also offers excellent color correction (known as "Super APO"), with tests only noting a lateral chromatism minor at the extreme edges of the full frame, easily corrected in post-processing. No marked longitudinal chromatic aberration (on centered stars) is reported, a sign of good color control over the entire useful wavelength range.

Anti-glare and contrast treatments : Although the data sheets do not detail the layers, both instruments feature multi-layer anti-reflective coatings on all optical surfaces, essential for maximizing transmission and contrast. The SQA106 features a very high transmission rate (MTF values > 0.9 at low spatial frequencies) thanks to the quality of its optics and processing. In practice, images obtained with either of these astrographs show very good contrast and tight stars, with no annoying halos on bright stars (the FRA600 with reducer showed no noticeable halos or ghosts on Rigel in a thorough test).

Corrected field and image circle : A major advantage of these glasses is their wide field of view corrected right out of the box, with no need for additional correctors. The Askar FRA600 provides an illuminated image circle of 66 mm diameter - far greater than the 24×36 format (43 mm diagonal). However, this 66 mm figure corresponds to total illumination; the portion of the field actually well corrected for star sharpness is closer to ~45 mm diameter according to field tests. In other words, on a full-format sensor (∅ ~44 mm), the FRA600 delivers sharp stars over almost the entire field (see performance section), while on a 33×44 mm medium-format sensor (55 mm diagonal) stars at the extreme edges start to degrade optically.

For its part, the SharpStar SQA106 boasts a circle corrected by 55 mm diameter, ideally covering 24×36 mm and extending to 33×44 mm. The distribution of illumination over the SQA106's field of view is excellent. > 90 % illumination at 22 mm from center (edge of a full-frame sensor) and ~75 % at the 27.5 mm from center (corner of a 44×33 mm sensor) . By comparison, the FRA600 also offers very even illumination on full-frame (moderate vignetting mainly due to the SLR body in the test), and remains usable on medium-format from a brightness point of view (corners at ~60% or more, with no mirror to obstruct). No severe vignetting with these two goggles, even on large sensors: their design with a large rear corrector (80 mm diameter doublet in the FRA600 ) makes it easy to illuminate a wide photographic field.

Astrophotography performance: flat fields, full-format sensors and aberrations

Dedicated to deep-sky imaging, the Askar FRA600 and SharpStar SQA106 have been field-tested with modern cameras, including APS-C, full format 24×36 mm and even medium format 33×44 mm. The results show that both instruments offer excellent overall performance, with some differences in the extreme corners of the image and in terms of flexibility.

Star quality in the field - On a APS-C sensor (~28 mm diagonal format), the stars are perfectly round and pitted to the edges for both scopes, without any additional correction. The SQA106, tested with an APS-C color sensor (ASI2600MC, 23×15 mm), showed stars "absolutely nothing to reproach" according to one user, with the corners as sharp as the center. The FRA600, with its longer focal length, also produces a perfectly flat and sharp field on APS-C, making it suitable for APS-C or 4/3 type cameras without any reservations.

On a full-format sensor (24×36 mm)both instruments cover the entire field with a high degree of sharpness, but the SQA106 features cleaner corners and virtually no chromatism. According to SharpStar's specifications, the quality difference between the center and the corner on the SQA106 is minimal: the RMS spot radius from <1.7 µm in the center to <2.2 µm in the corners . This means that even at the edges of the 24×36 format, the stars remain concentrated in a disk of ~2 µm radius, a fraction of a pixel for today's sensors (for example, 2 µm corresponds to 0.4 pixel on a sensor with 4.5 µm photosites). In practice, images taken with the SQA106 on a full frame show from punctual stars to cornerswithout coma or noticeable astigmatism. The coma and the field curvature are effectively zero thanks to the Petzval design, and no spherical aberration There is nothing to report on the plan.

The FRA600, with 600 mm f/5.6 (without gearbox)offers a very sharp center of field, approaching the performance of a reference like the Takahashi FSQ-106 according to one tester. However, on the full-format cornersa slight deterioration is observed: the stars in the four corners are a little tangentially stretched (elongation in the shape of a "radial coma/astigmatism) . This elongation remains moderate (eccentricity of around 0.5-0.6 in the corners) and the stars retain a generally acceptable shape - a far cry from the pronounced coma of some poorly corrected telescopes. Nevertheless, compared with the SQA106, the FRA600 native is a notch lower for image corners on full frame. An advanced user indicates that for optimal use on a 24×36 sensor, he considers the stars perfectly corrected on ~45 mm circle and the very edges (beyond 22 mm from the center) are "acceptable limits without being catastrophic. This performance is still quite respectable for a 108 mm lens at f/5.6 in this price range, and is judged to be "very good". "marginally acceptable on full frame by demanding testers. In a nutshell, on full format without additional corrector, the SQA106 takes the lead with more punctual stars in the corners, while the FRA600 shows slight astigmatism/coma aberrations at the edges (without rendering the field unusable - many users are happy with it as it is on full frame).

With regard tochromatic aberrationBoth instruments perform in exemplary fashion. The SQA106 shows almost no evidence of chromaticism on the stars, thanks to the use of SD lenses and optimized focusing across the entire spectrum. L'Askar FRA600 has negligible longitudinal chromatism and simply a slight lateral chromatism at the edge of the full-frame field (due to the corrector), resulting in tiny bangs of color around stars far from the center. This minor defect can be corrected by separating and realigning the R, G, B layers during image processing. With the reducer 0.7× (see next section), the FRA600 sees a little more lateral chromatism at the edges (the image spreads differently according to color), but here again, layer-by-layer registration in post-processing solves the problem to a large extent. Even at f/4.8, the SQA106 doesn't suffer from noticeable chromatism - an advantage of its high-end design.

Vignetting and field illumination : As mentioned above, the optical vignetting is very contained on both models. The manufacturer's measurements for the SQA106 show ~10% of light loss at the edges of the full frame (which is excellent), and ~25% of loss at the corners of a 33×44 mm sensor. The FRA600, with its 80 mm rear aperture, illuminates an even wider field (66 mm); on a full frame, a test showed that the sensor was fully informed (the slight vignetting measured was due mainly to the obstruction of the SLR mirror). Used with a mirrorless or astro camera (no reflex mirror)the FRA600 provides a very even illumination right to the corners 24×36 format. On a 33×44 format, the FRA600 without reducer continues to illuminate the sensor correctly (corners >60% illumination), as does the SQA106 (~75%). In all cases, a flat calibration will compensate for the slight residual vignetting. No shade due to the eyepiece holder has been reported (internal diameters are oversized to avoid this).

Backfocus and accessory mounting : In astrophotography, it's important to be able to insert various accessories (filter wheel, optical divider, electronic rotator, etc.) while retaining the ability to focus. In this respect, the FRA600 offers a generous rear draft of approx. 160 mm from the end of the rotator . This means that by removing or adding rings, you can insert numerous elements into the optical train (e.g. a camera with filter wheel and tilt corrector) without any focus problems. The SQA106, for its part, supports a print of 48 mm to 78 mm (55 mm is the recommended configuration). This ~30 mm backfocus range is designed to accommodate a typical SLR camera + adapter + filter. For complex assembliesThe SQA106 is a little more cramped, but still leaves plenty of room for an OAG, a filter wheel and, of course, the camera.

Impact of using the 0.7× gearbox with the FRA600

The Askar FRA600 has the unique feature of being able to be used with a dedicated 0.7× focal reducer (optional). The addition of this corrector-reducer significantly changes its characteristics and performance, so it is worth describing them in detail:

• Focal ratio and resultant field : With the 0.7× reducer, the focal length of the FRA600 increases from 600 mm to 420 mmand its focal ratio opens from f/5.6 to f/3,9 . The result is a approx. 2× illumination gain (the exposure time is halved for the same image depth) and a photographic field enlarged by a factor of 1.43 in linear terms (~2× larger field area). For example, an object spread over 2° of sky will occupy ~33% of the sensor in length at 600 mm, but ~47% of the sensor at 420 mm. This gain in field of view is highly appreciable for large nebulae or extended galaxies.
• Standardized backfocus : The FRA600's 0.7× reducer (a 4-element, 3″ diameter model) screws onto the rear of the eyepiece holder. It offers 55 mm optical draft to the sensor, which is exactly the distance of a DSLR with T2 ring, or a typical camera + filter wheel + optical splitter. This choice of a standard 55 mm makes it much easier to use: the reducer+FRA600 system can be treated like any conventional refractor + flattener in terms of backfocusing. The reducer also incorporates a 2″ (M48) filter thread within it, handy for adding an L-Pro or Hα filter without increasing the drawdown .
• Image circle and sensor coverage : This f/3.9 full-format gearbox has been designed to cover at least 24×36 mm. Sound free opening of approx. 70 mm is wide enough to illuminate a 44×33 mm sensor (55 mm diagonal) almost entirely. Illumination measurements show that with a mirrorless housing, the 24×36 field remains very well illuminated (corners not vignetted by the optics), and that the 33×44 format also receives abundant light (better than 60% illumination in the corners, which is comparable to other medium-format astrographs). In terms of sharpness on the other hand, the reducer improves the full-frame field but does not make the FRA600 miraculously perfect on medium format: tests show that on 44×33 sensors, image corners remain aberrant (coma/astigmatism) both without and with . The use of the reducer does not degrade the corrected circle, but it does not alter it.does not expand A full-frame sensor benefits from sharp stars right up to the edge with the reducer, while a 33×44 sensor will still have slightly blurred corners in both configurations. We can conclude that the FRA600+reducer is optimized for full format (and below), with medium format still usable but with poorer corners - similar to the native SQA106, which barely covers 33×44.
• Sharpness and aberration improvement : Adding the 0.7× reducer significantly refines star size and the overall optical correction of the FRA600. A quantitative test measured a decrease in stellar FWHM by ~20% with the reducer compared with the native configuration (smaller stars). Above all, the corner aberrations observed without the reducer are largely eliminated: with the reducer, stars at the edge of the full-format field become almost round and much sharper . Star eccentricity tends to even out at around ~0.58-0.62 across the entire field, with no marked elongation peaks in the corners. At f/3.9, the FRA600's corners thus offer performance that we judge to be "very good, especially for such an open instrument". . One tester goes so far as to say that he has thethe impression that the FRA600 has been optimized for use with its gearboxThe f/3.9 combo gives good results - which is the opposite of most other astrographs, where the native mode is optimal and the reducer a compromise. In a nutshell, the FRA600 delivers its best with the 0.7× gearbox. A wide field, very well corrected and extremely fast in terms of brightness.
• Residual aberrations with the reducer : The counterpart of this f/3.9 aperture is the appearance of slight lateral chromatic aberrations. As mentioned above, at the edge of the field there is a slight dispersion of colors (the stars may show a tiny red border on one side and a blue border on the other). This defect, known as "lateral coloris can be corrected in post-processing by shifting the color layers relative to each other. Aside from this lateral chromatism, no coma or spherical aberration of note is apparent with the reducer. A very positive point: no ghosting or halos on bright stars - a test on Rigel revealed no ghosting despite long, highly-stretched exposures, where some Takahashi correctors produce glare. This is indicative of the high quality optical design of this reducer (effective anti-reflective coatings and absence of highly curved lenses inducing reflections).

All in all, the use of the 0.7× gearbox takes the FRA600 into another category to obtain a 108 mm f/3.9 astrograph ultra-bright, delivering a field of view of 5.4° × 3.6° on a full-frame sensor, while retaining fine, round stars right up to the edges. This configuration is ideal for large diffuse objects (e.g. galaxies M31, M33, North America + Pelican nebulae in a single shot, etc.) or simply to drastically reduce integration times. Visit save installation time is particularly useful for SHO (narrowband) photography, where f/3.9 captures twice as much signal as f/5.6 in a given time. On the other hand, if you're looking for a longest focal length for smaller targets, we have the freedom to remove the reducer and return to 600mm at f/5.6 - at the cost of a slight loss of sharpness on the corners in full-frame. This 2-in-1 versatility is a clear advantage of the FRA600 over the SQA106, which has no known dedicated reducer (being already very open at f/4.8, there are no plans to reduce it further).

Comparative conclusion

To conclude, here's a comparative overview based on key criteria:

• Optical design and corrected field : The two astrographs are flat-field apochromatic quintuplets of the highest quality. La SQA106 offers an impeccably corrected field of view up to 24×36 format, and even 33×44 mm, thanks to its 55 mm image circle and SD lenses ensuring extreme sharpness over the entire field of view. L'Askar FRA600 has a 66 mm circle, but in practice its native corners are slightly less perfect on a full frame.
• Astrophotography performance (full format) : SQA106 excels right from the start, with spot-on stars and no noticeable aberration right up to the edges of the full frame, no correction required. FRA600 is very good in the center, but a little less good at the edges at 600 mm f/5.6, although still acceptable. With the 420 mm f/3.9 reducer, the FRA600 offers smaller stars and better corner control than at 600 mm, at the price of a lateral chromatism that needs to be corrected. For uncompromising full-frame imaging, the SQA106 provides the simplicity of an optimal native system, while the FRA600 can achieve comparable or even superior sharpness performance via the reduction accessory, which adds an optical element and a cost.
• Focal/speed versatility : Visit FRA600 scores a point with his removable reducer Two configurations are available in a single tube: 600mm f/5.6 for classic deep sky (or a bit of lunar planetary), and 420mm f/3.9 for ultra-bright wide-field. The SQA106 remains fixed at 509mm f/4.8 - already a very good wide-field compromise - but cannot be adjusted in focal length. Note that SharpStar has announced a "Ultra Cat 108 mm (WO RedCat 108) in f/2.8, but that's a different matter. The FRA600 is the only lens in the range to offer such modularity.
• Mechanical aspects : Both instruments are very well built. The FRA600 is a little more compact (tube <50 cm folded) but heavier on the mount (~6.5 kg vs. 5.8 kg) . Its 4.2″ focuser supports large loads (APN, FF camera + accessories) without batting an eyelid. The SQA106, with its longer tube, has a lower weight. balancing on the frame (~20 cm tube protruding from each side of the rings) but remains in the same weight category. Its unique collar facilitates quick set-up and slightly reduces weight. The SQA106's 2.8″ eyepiece holder is up to the task too, with easy rotation and appreciated motor compatibility . One advantage of the FRA600 is its strong back draft available (160 mm), allowing complex set-ups, whereas the SQA106 is optimized for ~55 mm of backfocus (sufficient for most standard imaging applications, however).
• Glass selection and chromatism : The SQA106 uses top-of-the-range SD lenses (maximum chromatic reduction), which can be seen in the absence of blue/red fringing on bright stars at f/4.8. The FRA600, although very well corrected (ED lenses), shows a hint of lateral chromatism at the edge of the full-frame field, particularly at f/3.9 . For color photography on an OSC sensor, the SQA106 will deliver clean stars without colorimetric retouching. On the FRA600, it may be necessary to adjust the layers in post-processing to obtain the same result at pixel level.

All in all, this FRA600 vs SQA106 duel concludes with a excellent performance from both astrographseach with its own strengths:

• L'Askar SQA106 is a "premium" instrument that delivers an immediate ultra-net flat field on full framewith optimized mechanics and optics (SD lenses, spot size <2.2 µm) for uncompromising astrophotography. It is particularly well-suited to imagers using large color or monochrome 24×36 sensors, who want impeccable quality without additional adjustments. Product sheet available below:

• L'Askar FRA600 offers a highly successful and evolutionary at a more contained price (~2,599 $ per tube). Without the reducer, it already produces very fine images on APS-C and full-frame, with just a slight weakness at the extreme corners. By adding the reducer 0.7× (approx. 400-450 $), we obtain a f/3.9 astrograph that will delight all fans of large, fast field. In the end, this tube+reducer duo is a little less expensive than the SQA106 alone, while still offering a high level of performance. flexibility 600 mm vs 420 mm welcome. The downside is the management of an additional optical element and a slight chromatism to be processed in image processing for optimum results on stars. Product sheet available below:

Last but not least, these two instruments, from the same manufacturer (Jiaxing SharpStar/Askar), bear witness to recent advances in amateur optics. compete with benchmarks like the Takahashi FSQ-106, while offering modern features (massive rotating eyepiece holder, medium-format sensor compatibility, etc.). The choice between the FRA600 and the SQA106 will therefore depend above all on your needs. priorities : speed and versatility (FRA600 + gearbox) or high-end simplicity (native SQA106) - in both cases, you'll have an excellent instrument for astrophotography.

Sources : Independent tests (CloudyNights) of whwang on FRA600, user discussions on SQA106, SharpStar/Askar datasheets and resellers (HighPoint Scientific).