FOVMath

Askar SQA, FRA and PHQ astrographs: designs, reducers and back-focus reference points

Askar, a brand of Sharpstar Optics, sells three self-flattening astrograph lines: SQA Petzvals at f/4.6–f/4.8 with no reducer, FRA quintuplets at f/5–f/5.6 with 0.7x reducers, and PHQ refractors at f/6.4–f/7.7 with 0.7x–0.76x reducers. Askar publishes most reduced focal lengths outright, but its back-focus figures start from different threads.

Published October 15, 2026 . Sources are listed at the end of the page.

Askar SQA, FRA and PHQ: published specifications
Model Design Aperture (mm) Focal length (mm) Focal ratio Image circle (mm) Back focus (mm) Weight (kg) Official reducer or flattener
SQA55 Quintuplet air-spaced Petzval APO (one SD glass, one ED glass) 55 264 f/4.8 44 55 1.84 none listed on the product page
SQA60 pro Sextuplet air-spaced Petzval APO (2 SD glass elements) 60 276 f/4.6 44 55 2.79 none listed on the product page
SQA70 Quintuplet air-spaced Petzval APO (2 ED glass elements) 70 336 f/4.8 44 55 2.68 none listed on the product page
SQA85 Quintuplet air-spaced Petzval APO (2 SD glass elements) 85 408 f/4.8 not published 55 3.64 none listed on the product page
SQA106 Quintuplet air-spaced Petzval APO (2 SD glass elements) 106 509 f/4.8 55 55 5.82 none listed on the product page
SQA130 Quintuplet air-spaced Petzval APO (2 SD glass elements) 130 624 f/4.8 55 55 9.18 none listed on the product page
65PHQ Quintuplet air-spaced APO with two ED glass (self-flattening flat-field astrograph) 65 416 f/6.4 44 not published 2 65PHQ 0.75x Full-Frame Reducer: 312 mm, f/4.8
80PHQ Quadruplet air-spaced APO with two ED glass (3+1 integrated flat-field design) 80 600 f/7.5 44 not published 3.9 80PHQ 0.76x Full Frame Reducer: 456 mm, f/5.7
107PHQ Quadruplet air-spaced APO with two ED glass (built-in flat-field lens) 107 749 f/7 44 not published 5.7 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer: 524 mm, f/4.9
130PHQ Quadruplet air-spaced APO with two ED glass (self-flattening) 130 1000 f/7.7 60 not published 10.5 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer: 700 mm, f/5.4
151PHQ Quadruplet air-spaced APO with two ED glass (self-flattening) 151 1057 f/7 60 not published 11.6 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer: 740 mm, f/4.9
FRA300 Pro Quintuplet fully air-spaced Petzval APO (one ED glass) 60 300 f/5 44 not published 2.26 none listed on the product page
FRA400 Quintuplet dual-ED air-spaced APO flat-field refractive astrograph 72 400 f/5.6 44 140 2.56 F3.9 Full Frame Reducer for FRA400/FRA500: 280 mm, f/3.9
FRA400C Quintuplet dual-ED air-spaced APO 72 400 f/5.6 44 55 2.68 FRA400C 0.7x Full-Frame Reducer: 280 mm, f/3.9
FRA500 Quintuplet air-spaced APO with two ED glass (flat-field) 90 500 f/5.6 55 not published 4.1 F3.9 Full Frame Reducer for FRA400/FRA500: 350 mm, f/3.9
FRA600 Quintuplet flat-field APO with two ED elements 108 600 f/5.6 66 160 6.5 F3.9 Full Frame Reducer for FRA600: 420 mm, f/3.9

Askar is Sharpstar

Sharpstar Optics’ about page names Sharpstar and Askar as the company’s two brands and introduces Askar as its newer one. Askar product pages, manuals and reducers all live on sharpstar-optics.com, which is why this site cites them there. The Sharpstar-branded reflectors and refractors are on the Sharpstar page.

Three lines at three speeds

The SQA line is the fastest refractive group: Petzval designs from the SQA55 (264 mm, f/4.8) to the SQA130 (624 mm, f/4.8), with the six-element SQA60 pro at f/4.6. Askar lists no reducer for any of them. Image circles are 44 mm for the 55, 60 pro and 70, 55 mm for the 106 and 130; the SQA85 page says only “Full-frame”, so its circle is not published as a number.

The FRA line runs f/5 to f/5.6, from the FRA300 Pro (60 mm aperture, 300 mm) to the FRA600 (108 mm, 600 mm, 66 mm circle). The PHQ tubes are slower still, f/6.4 to f/7.7 at 416–1057 mm, and their pages stress that no flattener is needed.

Focal ratio means something concrete when focal length is held fixed. The SQA85 (85 mm, 408 mm) and FRA400 (72 mm, 400 mm) frame almost the same field, 3.36° × 2.25° for the FRA400 on an ASI2600MC Pro. The SQA85’s larger objective gathers (85 ÷ 72)² = 1.39 times as much light from each object onto pixels of nearly the same angular size; that is the f/4.8 versus f/5.6 difference.

Reducers with published focal lengths

Askar prints the reduced focal length for most combinations, and the figures match native focal length × factor:

TelescopeReducerPublished resultNative × factor
65PHQ0.75x312 mm, f/4.8312 mm
80PHQ0.76x456 mm, f/5.7456 mm
107PHQ0.7x universalnot published524 mm
130PHQ0.7x universal700 mm, f/5.4700 mm
151PHQ0.7x universal740 mm, f/4.9740 mm
FRA400F3.9, 0.7x280 mm280 mm
FRA400C0.7x280 mm, f/3.9280 mm
FRA500F3.9, 0.7xf/3.9 only350 mm
FRA600F3.9, 0.7x420 mm420 mm

Going from f/5.6 to f/3.9 on an FRA raises the per-pixel signal rate on extended objects by (5.6 ÷ 3.9)² = 2.06, at a scale 1.43 times coarser. The reducers themselves use a 55 mm back focus. The reducer calculator handles the 107PHQ and FRA500 cases where only the factor is printed.

Back focus starts from different threads

The spec table’s back-focus column mixes reference points, so the numbers are not comparable at a glance:

  • SQA tubes and the FRA400C: a recommended 55 mm connection length, with a supported range (50–60 mm on the SQA55, 46–76 mm on the SQA130).
  • FRA400: 140 mm, measured from the end of the rotator’s M68×1 thread.
  • FRA600: 160 mm from the end of the rotator’s M90×1 thread; its sectional adapter steps down through M68 and M54 to M48.
  • FRA500: no single value, but a maximum connection range of 85 mm from the M48 base on the conical extender, or 158 mm from the M86 rotator thread.
  • PHQ and FRA300 Pro: no single value; the pages give maximum accessory connection distances instead.

Before buying spacers, convert each figure to the same reference, usually the M48 face your camera adapter threads onto. The back focus guide shows the bookkeeping.

Field of view with common sensors

Width × height of the field and image scale for ZWO ASI2600MC Pro (IMX571), ZWO ASI533MC Pro (IMX533), ZWO ASI585MC (IMX585), ZWO ASI6200MC Pro (IMX455), computed from each camera's published pixel count and pixel size. Reducer focal lengths are the manufacturer's figure where published, otherwise native focal length × the published factor.

Telescope and configuration Focal length ASI2600MC ProASI533MC ProASI585MCASI6200MC Pro
SQA55, native 264 mm 5.10° × 3.41° 2.94″/px 2.45° × 2.45° 2.94″/px 2.42° × 1.36° 2.27″/px 7.80° × 5.21° 2.94″/px
SQA60 pro, native 276 mm 4.87° × 3.26° 2.81″/px 2.35° × 2.35° 2.81″/px 2.31° × 1.30° 2.17″/px 7.46° × 4.98° 2.81″/px
SQA70, native 336 mm 4.00° × 2.68° 2.31″/px 116′ × 116′ 2.31″/px 114′ × 64′ 1.78″/px 6.13° × 4.09° 2.31″/px
SQA85, native 408 mm 3.30° × 2.20° 1.90″/px 95′ × 95′ 1.90″/px 94′ × 53′ 1.47″/px 5.05° × 3.37° 1.90″/px
SQA106, native 509 mm 2.64° × 1.77° 1.52″/px 76′ × 76′ 1.52″/px 75′ × 42′ 1.18″/px 4.05° × 2.70° 1.52″/px
SQA130, native 624 mm 2.16° × 1.44° 1.24″/px 62′ × 62′ 1.24″/px 61′ × 35′ 0.96″/px 3.31° × 2.21° 1.24″/px
65PHQ, native 416 mm 3.23° × 2.16° 1.86″/px 93′ × 93′ 1.86″/px 92′ × 52′ 1.44″/px 4.96° × 3.31° 1.86″/px
65PHQ, 65PHQ 0.75x Full-Frame Reducer 312 mm 4.31° × 2.88° 2.49″/px 2.08° × 2.08° 2.49″/px 2.04° × 1.15° 1.92″/px 6.60° × 4.41° 2.49″/px
80PHQ, native 600 mm 2.24° × 1.50° 1.29″/px 65′ × 65′ 1.29″/px 64′ × 36′ 1.00″/px 3.44° × 2.29° 1.29″/px
80PHQ, 80PHQ 0.76x Full Frame Reducer 456 mm 2.95° × 1.97° 1.70″/px 85′ × 85′ 1.70″/px 84′ × 47′ 1.31″/px 4.52° × 3.02° 1.70″/px
107PHQ, native 749 mm 108′ × 72′ 1.04″/px 52′ × 52′ 1.04″/px 51′ × 29′ 0.80″/px 2.75° × 1.84° 1.04″/px
107PHQ, 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer 524 mm 2.57° × 1.72° 1.48″/px 74′ × 74′ 1.48″/px 73′ × 41′ 1.14″/px 3.94° × 2.63° 1.48″/px
130PHQ, native 1000 mm 81′ × 54′ 0.78″/px 39′ × 39′ 0.78″/px 38′ × 22′ 0.60″/px 2.06° × 1.38° 0.78″/px
130PHQ, 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer 700 mm 115′ × 77′ 1.11″/px 56′ × 56′ 1.11″/px 55′ × 31′ 0.85″/px 2.95° × 1.97° 1.11″/px
151PHQ, native 1057 mm 76′ × 51′ 0.73″/px 37′ × 37′ 0.73″/px 36′ × 20′ 0.57″/px 117′ × 78′ 0.73″/px
151PHQ, 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer 740 mm 109′ × 73′ 1.05″/px 53′ × 53′ 1.05″/px 52′ × 29′ 0.81″/px 2.79° × 1.86° 1.05″/px
FRA300 Pro, native 300 mm 4.48° × 3.00° 2.59″/px 2.16° × 2.16° 2.59″/px 2.13° × 1.20° 1.99″/px 6.87° × 4.58° 2.59″/px
FRA400, native 400 mm 3.36° × 2.25° 1.94″/px 97′ × 97′ 1.94″/px 96′ × 54′ 1.50″/px 5.15° × 3.44° 1.94″/px
FRA400, F3.9 Full Frame Reducer for FRA400/FRA500 280 mm 4.80° × 3.21° 2.77″/px 2.31° × 2.31° 2.77″/px 2.28° × 1.28° 2.14″/px 7.36° × 4.91° 2.77″/px
FRA400C, native 400 mm 3.36° × 2.25° 1.94″/px 97′ × 97′ 1.94″/px 96′ × 54′ 1.50″/px 5.15° × 3.44° 1.94″/px
FRA400C, FRA400C 0.7x Full-Frame Reducer 280 mm 4.80° × 3.21° 2.77″/px 2.31° × 2.31° 2.77″/px 2.28° × 1.28° 2.14″/px 7.36° × 4.91° 2.77″/px
FRA500, native 500 mm 2.69° × 1.80° 1.55″/px 78′ × 78′ 1.55″/px 77′ × 43′ 1.20″/px 4.12° × 2.75° 1.55″/px
FRA500, F3.9 Full Frame Reducer for FRA400/FRA500 350 mm 3.84° × 2.57° 2.22″/px 111′ × 111′ 2.22″/px 109′ × 62′ 1.71″/px 5.89° × 3.93° 2.22″/px
FRA600, native 600 mm 2.24° × 1.50° 1.29″/px 65′ × 65′ 1.29″/px 64′ × 36′ 1.00″/px 3.44° × 2.29° 1.29″/px
FRA600, F3.9 Full Frame Reducer for FRA600 420 mm 3.20° × 2.14° 1.85″/px 93′ × 93′ 1.85″/px 91′ × 51′ 1.42″/px 4.91° × 3.28° 1.85″/px

Try another camera in the field of view calculator, or check star sampling for your sky with the sampling calculator.

Questions

Are Askar and Sharpstar the same company?
Yes. Sharpstar Optics' about page lists Sharpstar and Askar as the company's two brands, and the Askar product pages are hosted on sharpstar-optics.com.
Why does the FRA400 list 140 mm of back focus when the SQA lines list 55 mm?
The FRA400 figure is measured from the end of its rotator's M68 thread, while the SQA figures are recommended connection lengths at the M48 adapter. They start from different reference points, so the two numbers can't be compared directly.
  • Askar APO, F and N series Askar APO triplets (700–1421 mm), self-flattened F refractors and f/3.6 N Newtonians: reducer focal lengths, a 28 mm image circle, and which sensors fit.
  • Sharpstar astrographs Sharpstar f/2.8 HNT Newtonians, SCA260 and SCA310 Cassegrains and the Z4 refractor: image circles, obstruction, and which EDPH models are discontinued.
  • Back focus and spacing What back focus is, why reducers and flatteners need an exact sensor distance, published values for real telescopes, and how to add up a spacer chain.
  • Reducer and Barlow Effective focal length, focal ratio, image scale and field with a reducer or Barlow, from its nominal factor or from lens focal length and spacing.
  • Small refractors under 400 mm Sixteen small refractors from 178 to 408 mm compared on APS-C field, image scale, focal ratio and image circle against APS-C and full-frame diagonals.

Sources

References for the text first, then the manufacturer specification pages for the telescopes and the reference cameras.

  1. About Sharpstar Optics Jiaxing Sharpstar Optical Instrument Co., Ltd.. Accessed October 12, 2026.
  2. 65PHQ 0.75x Full-Frame Reducer Sharpstar Optics (Askar). Accessed October 12, 2026.
  3. 80PHQ 0.76x Full Frame Reducer Sharpstar Optics (Askar). Accessed October 12, 2026.
  4. 107PHQ/130PHQ/151PHQ 0.7x Universal Reducer Sharpstar Optics (Askar). Accessed October 12, 2026.
  5. F3.9 Full Frame Reducer for FRA400/FRA500 Sharpstar Optics (Askar). Accessed October 12, 2026.
  6. F3.9 Full Frame Reducer for FRA600 Sharpstar Optics (Askar). Accessed October 12, 2026.
  7. FRA400C 0.7x Full-Frame Reducer Sharpstar Optics (Askar). Accessed October 12, 2026.
  8. Askar SQA55 specifications Askar. Accessed October 12, 2026.
  9. Askar SQA60 pro specifications Askar. Accessed October 12, 2026.
  10. Askar SQA70 specifications Askar. Accessed October 12, 2026.
  11. Askar SQA85 specifications Askar. Accessed October 12, 2026.
  12. Askar SQA106 specifications Askar. Accessed October 12, 2026.
  13. Askar SQA130 specifications Askar. Accessed October 12, 2026.
  14. Askar 65PHQ specifications Askar. Accessed October 12, 2026.
  15. Askar 80PHQ specifications Askar. Accessed October 12, 2026.
  16. Askar 107PHQ specifications Askar. Accessed October 12, 2026.
  17. Askar 130PHQ specifications Askar. Accessed October 12, 2026.
  18. Askar 151PHQ specifications Askar. Accessed October 12, 2026.
  19. Askar FRA300 Pro specifications Askar. Accessed October 12, 2026.
  20. Askar FRA400 specifications Askar. Accessed October 12, 2026.
  21. Askar FRA400C specifications Askar. Accessed October 12, 2026.
  22. Askar FRA500 specifications Askar. Accessed October 12, 2026.
  23. Askar FRA600 specifications Askar. Accessed October 12, 2026.
  24. ZWO ASI2600MC Pro specifications ZWO. Accessed October 12, 2026.
  25. ZWO ASI533MC Pro specifications ZWO. Accessed October 12, 2026.
  26. ZWO ASI585MC specifications ZWO. Accessed October 12, 2026.
  27. ZWO ASI6200MC Pro specifications ZWO. Accessed October 12, 2026.