{"id":8655,"date":"2025-06-25T11:27:27","date_gmt":"2025-06-25T09:27:27","guid":{"rendered":"https:\/\/deep-space-astronomy.ch\/?p=8655"},"modified":"2025-07-08T16:15:06","modified_gmt":"2025-07-08T14:15:06","slug":"askar-fra600-vs-sqa106","status":"publish","type":"post","link":"https:\/\/deep-space-astronomy.ch\/en\/askar-fra600-vs-sqa106\/","title":{"rendered":"An Askar FRA600 or the SQA106?"},"content":{"rendered":"
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The astrograph Askar FRA600<\/strong> 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.<\/p>\n\n\n\n

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The apochromatic telescope SQA106<\/strong> (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<\/strong> very low dispersion) to provide a wide image circle of 55 mm<\/strong> corrected, covering full-format and even medium-format sensors . The stars remain fine and punctual over the entire field (RMS spot size <2.2 \u00b5m at the corner of the 24\u00d736 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" (\u224871 mm) Crayford eyepiece holder with 30 mm of travel and a 360\u00b0 rotator<\/strong> graduated for framing . A set of rear adapters (M68, M54, M48) is supplied for easy connection to any type of camera.<\/p>\n\n\n\n

Mechanical details: weight, dimensions and equipment<\/strong><\/h2>\n\n\n\n

Both instruments feature a high level of finish, suitable for demanding astrophotography. The table below summarizes their main mechanical characteristics:<\/p>\n\n\n\n

Mechanical characteristics<\/strong><\/th>Askar FRA600<\/strong> (108 mm f\/5.6)<\/strong><\/th>Askar SQA106 (106 mm f\/4.8)<\/strong><\/th><\/tr><\/thead>
Tube length<\/strong> (fog shield retracted)<\/td>~493 mm<\/td>~516 mm (retracted), 586 mm (extended)<\/td><\/tr>
Tube diameter<\/strong><\/td>125 mm<\/td>~115 - 120 mm (estimate, not specified)<\/td><\/tr>
Tube weight<\/strong><\/td>6.5 kg (with Losmandy collars & tail)<\/td>5.82 kg (bare OTA), ~8.12 kg with collar & tail<\/td><\/tr>
Lens holder<\/strong><\/td>Crayford rack 4.2\u2033, gear ratio 1:10 (high load capacity)<\/td>Crayford 2.8\u2033 gearbox (30 mm stroke) (motorizable)<\/td><\/tr>
Angle rotator<\/strong><\/td>Yes - integrated (M90x1 threaded ring)<\/td>Yes - integrated 360\u00b0 with graduated scale<\/td><\/tr>
Rear thread<\/strong><\/td>M90 \u00d7 1 (rotator) + M68\/M54\/M48 adapters (+ 2\u2033\/1.25\u2033 runner)<\/td>M68\/M54\/M48 (adapters supplied)<\/td><\/tr>
Fasteners & accessories<\/strong><\/td>Two clamps + multifunction handle (M6\/M4), 300 mm Losmandy shank, M54 & M48 bushings<\/td>One-piece clamp\/handle (openwork) with M4\/M6 pitch, 300 mm Losmandy shank, soft carrying case<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Weight and dimensions :<\/strong> The FRA600 weighs approximately 6.5 kg<\/strong> 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).<\/p>\n\n\n\n

Eyepiece holder and mechanical compatibility :<\/strong> Askar FRA600 features a large eyepiece holder 4.2 inches<\/strong> 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\u2033<\/strong>(i.e. ~71 mm), which is also rack-and-pinion geared. It offers 30 mm of travel and is compatible with<\/strong> of the market. Each bezel incorporates a field rotator<\/strong> This graduated rotator allows the camera to be rotated through 360\u00b0 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.<\/p>\n\n\n\n

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Both instruments come with threaded adapters for easy connection of various accessories. The FRA600 offers an M90\u00d71 (rotator) thread that can be reduced via tapered adapters to M68, M54 or M48 - in addition, eyepiece holders with 2\u2033 and 1.25\u2033 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<\/strong>\u00a0All 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.<\/p>\n\n\n\n

Clamps and fasteners :<\/strong> The Askar FRA600 is equipped with two necklaces<\/strong> 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<\/strong> 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<\/strong> (~11.8\u2033 long) ensuring stable attachment to the equatorial mount . The SQA106 also comes with a quilted Oxford fabric carrying case to protect the tube.<\/p>\n\n\n\n

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Internal construction quality :<\/strong> The inside of both tubes is matt and fitted with baffles to suppress stray reflections. The SQA106 in particular uses a matt black paintwork<\/strong> 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,<\/strong> 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.<\/p>\n\n\n\n

Optical details: aperture, focal length, design and coating<\/strong><\/h2>\n\n\n\n

Optically, both instruments are astrographs with flat field<\/strong> 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:<\/p>\n\n\n\n

Optical characteristics<\/strong><\/th>Askar FRA600<\/strong> (Quintuplet APO)<\/strong><\/th>SQA106 (Quintuplet SD APO)<\/strong><\/th><\/tr><\/thead>
Opening<\/strong> (diameter)<\/td>108 mm (4.25\u2033)<\/td>106 mm (4.17\u2033)<\/td><\/tr>
Focal length<\/strong> (native)<\/td>600 mm<\/td>509 mm<\/td><\/tr>
Focus report<\/strong> (focal length\/diameter)<\/td>f\/5,6<\/td>f\/4,8<\/td><\/tr>
Optical package<\/strong><\/td>Petzval quintuplet (triplet + doublet) with 2 glasses ED<\/strong> (Extra-low Dispersion)<\/td>Petzval Quintuplet (5 air-spaced lenses) with 2 lenses SD<\/strong> (Super ED)<\/td><\/tr>
Optical treatments<\/strong><\/td>Multilayer anti-reflective (all surfaces)<\/td>High-performance multilayer (high-transmission SD glass)<\/td><\/tr>
Corrected image circle<\/strong><\/td>66 mm diameter (flat field announced) - full format<\/strong> covered (\u2205 ~44 mm); illumination ~100% on 24\u00d736<\/td>55 mm diameter (plane field) - native full format (\u2205 44 mm) and medium format<\/strong> up to \u2205 55 mm (illumination ~90% at 44 mm, ~75% at 55 mm)<\/td><\/tr>
Aberration correction<\/strong><\/td>Apochromatic (reduced chromatic aberration), slight corner aberration on full format (see performance)<\/td>Apochromatic (SD lenses minimize chromatism), correction right to the corners of the 24\u00d736 field (~2 \u00b5m spots)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Aperture and field :<\/strong> The Askar FRA600 is an instrument for 108 mm<\/strong> diameter, slightly larger than the 106 mm<\/strong> 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<\/strong> (f\/5.6), while the SQA106 is shorter, 509 mm<\/strong> (f\/4,8) . The SQA106 is therefore approximately 1 IL<\/strong> brighter than the native FRA600 (f\/4.8 vs. f\/5.6), enabling ~1.36\u00d7 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\u00b0 on the long side of a full-frame sensor, vs. ~5.5\u00b0 for 509 mm).<\/p>\n\n\n\n

Optical design and ED\/SD glass :<\/strong> Both glasses use a apochromatic quintuplet<\/strong>. The FRA600 consists of a front triplet<\/strong> and a rear doublet<\/strong> field corrector, two of which are made of low-dispersion ED glass. The SQA106 also features 5 elements<\/strong> (air-spaced system), with two glass lenses SD<\/strong> (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<\/strong> 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<\/strong> 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.<\/p>\n\n\n\n

Anti-glare and contrast treatments :<\/strong> 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<\/strong> (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).<\/p>\n\n\n\n

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Corrected field and image circle :<\/strong> A major advantage of these glasses is their wide field of view<\/strong> corrected right out of the box, with no need for additional correctors. The Askar FRA600 provides an illuminated image circle of 66 mm<\/strong> diameter - far greater than the 24\u00d736 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<\/strong> diameter according to field tests. In other words, on a full-format sensor (\u2205 ~44 mm), the FRA600 delivers sharp stars over almost the entire field (see performance section), while on a 33\u00d744 mm medium-format sensor (55 mm diagonal) stars at the extreme edges start to degrade optically. <\/p>\n\n\n\n

For its part, the SharpStar SQA106 boasts a circle corrected by 55 mm<\/strong> diameter, ideally covering 24\u00d736 mm and extending to 33\u00d744 mm. The distribution of illumination over the SQA106's field of view is excellent. > 90 % illumination at 22 mm from center<\/strong> (edge of a full-frame sensor) and ~75 % at the 27.5 mm from center<\/strong> (corner of a 44\u00d733 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<\/strong> 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<\/strong>.<\/p>\n\n\n\n

Astrophotography performance: flat fields, full-format sensors and aberrations<\/strong><\/h2>\n\n\n\n

Dedicated to deep-sky imaging, the Askar FRA600 and SharpStar SQA106 have been field-tested with modern cameras, including APS-C, full format 24\u00d736 mm and even medium format 33\u00d744 mm<\/strong>. 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.<\/p>\n\n\n\n

Star quality in the field<\/strong> - On a APS-C sensor<\/strong> (~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\u00d715 mm), showed stars \"absolutely nothing to reproach\"<\/strong> 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.<\/p>\n\n\n\n

On a full-format sensor (24\u00d736 mm)<\/strong>both instruments cover the entire field with a high degree of sharpness, but the SQA106 features cleaner corners and virtually no chromatism<\/strong>. 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 \u00b5m in the center to <2.2 \u00b5m in the corners<\/strong> . This means that even at the edges of the 24\u00d736 format, the stars remain concentrated in a disk of ~2 \u00b5m radius, a fraction of a pixel for today's sensors (for example, 2 \u00b5m corresponds to 0.4 pixel on a sensor with 4.5 \u00b5m photosites). In practice, images taken with the SQA106 on a full frame show from punctual stars to corners<\/strong>without coma or noticeable astigmatism. The coma<\/strong> and the field curvature<\/strong> are effectively zero thanks to the Petzval design, and no spherical aberration<\/strong> There is nothing to report on the plan.<\/p>\n\n\n\n

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FRA600 spot diagram<\/figcaption><\/figure>\n\n\n\n
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Spot diagram of the SQA106, showing superior performance. <\/figcaption><\/figure>\n\n\n\n

The FRA600, with 600 mm f\/5.6 (without gearbox)<\/strong>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 corners<\/strong>a slight deterioration is observed: the stars in the four corners are a little tangentially stretched<\/strong> (elongation in the shape of a \"radial coma\/astigmatism)<\/strong> . 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<\/em> is a notch lower for image corners on full frame. An advanced user indicates that for optimal use on a 24\u00d736 sensor, he considers the stars perfectly corrected on ~45 mm circle<\/strong> and the very edges (beyond 22 mm from the center) are \"acceptable limits<\/em> 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<\/strong> on full frame by demanding testers. In a nutshell, on full format without additional corrector, the SQA106 takes the lead<\/strong> 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).<\/p>\n\n\n\n

With regard tochromatic aberration<\/strong>Both instruments perform in exemplary fashion. The SQA106<\/strong> shows almost no evidence of chromaticism<\/strong> on the stars, thanks to the use of SD lenses and optimized focusing across the entire spectrum. L'Askar FRA600<\/strong> has negligible longitudinal chromatism and simply a slight lateral chromatism<\/strong> 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\u00d7<\/strong> (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.<\/p>\n\n\n\n

Vignetting and field illumination :<\/strong> As mentioned above, the optical vignetting<\/strong> 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\u00d744 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<\/strong> (the slight vignetting measured was due mainly to the obstruction of the SLR mirror). Used with a mirrorless or astro camera (no reflex mirror)<\/strong>the FRA600 provides a very even illumination right to the corners<\/strong> 24\u00d736 format. On a 33\u00d744 format, the FRA600 without reducer continues to illuminate the sensor correctly (corners >60% illumination), as does the SQA106 (~75%). In all cases, a flat <\/strong>calibration will compensate for the slight residual vignetting. No shade<\/strong> due to the eyepiece holder has been reported (internal diameters are oversized to avoid this).<\/p>\n\n\n\n

Backfocus and accessory mounting :<\/strong> 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<\/strong> 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<\/strong> (55 mm is the recommended configuration). This ~30 mm backfocus range is designed to accommodate a typical SLR camera + adapter + filter. For complex assemblies<\/strong>The SQA106 is a little more cramped, but still leaves plenty of room for an OAG, a filter wheel and, of course, the camera. <\/p>\n\n\n\n

Impact of using the 0.7\u00d7 gearbox with the FRA600<\/strong><\/h2>\n\n\n\n

The Askar FRA600 has the unique feature of being able to be used with a dedicated 0.7\u00d7 focal reducer<\/strong> (optional). The addition of this corrector-reducer significantly changes its characteristics and performance, so it is worth describing them in detail:<\/p>\n\n\n\n