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Field Flatteners & Reducers

Most refractors and Schmidt-Cassegrains focus light onto a slightly curved surface, while camera sensors are flat. The centre stays sharp, but toward the corners stars stretch into lines. A field flattener corrects the curvature so stars stay round across the sensor. A reducer-flattener does the same and also shortens the focal length, for a wider field and faster exposures.

Each corrector is designed for specific telescopes and a specific back-focus. We carry flatteners and reducers from Askar, William Optics, Sky-Watcher, Celestron, SharpStar, Baader, ZWO, Starizona, Tele Vue, SVBONY and Explore Scientific, and we will tell you which one belongs on your tube.

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Starizona HyperStar 14 v4
$1,399.00 USD - $1,528.00 USD
$1,399.00 USD - $1,528.00 USD
$1,399.00 USD - $1,528.00 USD
$1,399.00 USD

Starizona HyperStar 14 v4

Converts Celestron C14 telescopes to an f/2 optical system 715 mm focal length 25× faster imaging than the native f/10 focal ratio 3.45° coma-free...

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$1,399.00 USD - $1,528.00 USD
$1,399.00 USD - $1,528.00 USD
$1,399.00 USD - $1,528.00 USD
$1,399.00 USD
Starizona HyperStar 6 v4
$499.00 USD - $628.00 USD
$499.00 USD - $628.00 USD
$499.00 USD - $628.00 USD
$499.00 USD

Starizona HyperStar 6 v4

Converts a Celestron C6 SCT into an f/1.9 astrograph 300 mm focal length provides a massive 4.1° field of view 25× faster than the telescope's nat...

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$499.00 USD - $628.00 USD
$499.00 USD - $628.00 USD
$499.00 USD - $628.00 USD
$499.00 USD
$1,299.00 USD - $1,428.00 USD
$1,299.00 USD - $1,428.00 USD
$1,299.00 USD - $1,428.00 USD
$1,299.00 USD

Starizona HyperStar V4 for Celestron 11"

Converts Celestron 11" SCT/EdgeHD to an f/1.9 imaging system 540mm focal length for wide-field astrophotography Delivers a 3.7° coma-free, flat fi...

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$1,299.00 USD - $1,428.00 USD
$1,299.00 USD - $1,428.00 USD
$1,299.00 USD - $1,428.00 USD
$1,299.00 USD
$999.00 USD - $1,128.00 USD
$999.00 USD - $1,128.00 USD
$999.00 USD - $1,128.00 USD
$999.00 USD

Starizona HyperStar V4 for Celestron 8"

Converts Celestron 8" SCTs to an f/1.9 imaging system 390mm focal length provides a massive 4.1° field of view Illuminates sensors up to 28mm in d...

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$999.00 USD - $1,128.00 USD
$999.00 USD - $1,128.00 USD
$999.00 USD - $1,128.00 USD
$999.00 USD
$1,199.00 USD - $1,328.00 USD
$1,199.00 USD - $1,328.00 USD
$1,199.00 USD - $1,328.00 USD
$1,199.00 USD

Starizona HyperStar V4 for Celestron 9.25"

Converts Celestron 9.25" SCTs to an f/2.2 optical system Reduces focal length to 525mm for wide-field imaging Delivers a coma-free, flat field of ...

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$1,199.00 USD - $1,328.00 USD
$1,199.00 USD - $1,328.00 USD
$1,199.00 USD - $1,328.00 USD
$1,199.00 USD
Starizona SCT Corrector IV - 0.63x Reducer / Coma Corrector in the box with the 35.3 mm M42 spacer
Starizona SCT Corrector IV - 0.63x Reducer / Coma Corrector
$399.00 USD - $399.00 USD
$399.00 USD
$399.00 USD - $399.00 USD
$399.00 USD

Starizona SCT Corrector IV - 0.63x Reducer / Coma Corrector

Reduces focal ratio by a factor of 0.63x, making your telescope 2.5x faster Corrects for off-axis coma inherent in Schmidt-Cassegrain designs Prov...

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$399.00 USD - $399.00 USD
$399.00 USD
$399.00 USD - $399.00 USD
$399.00 USD
$499.00 USD - $499.00 USD
$499.00 USD
$499.00 USD - $499.00 USD
$499.00 USD

Starizona SCT Corrector LF - Large Format Reducer/Coma Corrector

Focal Reducer: 0.7x, f/7 on a C11 and f/7.2 on a C14 Coma Corrector: Corrects inherent off-axis coma in standard SCTs Image Circle: 42mm, desig...

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$499.00 USD - $499.00 USD
$499.00 USD
$499.00 USD - $499.00 USD
$499.00 USD
Svbony 0.5x Focal Reducer 1.25" for Telescope Photography & Observing
$15.19 USD - $15.19 USD
$15.19 USD
$15.19 USD - $15.19 USD
$15.19 USD

SVBONY 0.5X Focal Reducer - 1.25"

Reduces telescope focal length by a 0.5x factor Fits standard 1.25" eyepieces and accessories Threads on via standard M28.5x0.6 filter threads Ful...

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$15.19 USD - $15.19 USD
$15.19 USD
$15.19 USD - $15.19 USD
$15.19 USD
SVBONY SV193 0.8X Focal Reducer / Field Flattener - 2"
SVBONY SV193 0.8X Focal Reducer / Field Flattener - 2"
$83.59 USD - $83.59 USD
$83.59 USD
$83.59 USD - $83.59 USD
$83.59 USD

SVBONY SV193 0.8X Focal Reducer / Field Flattener - 2"

0.8x Focal Reduction Factor Specifically designed for the SVBONY SV503 102ED Telescope Corrects for field curvature for flat, sharp stars 3-Elemen...

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$83.59 USD - $83.59 USD
$83.59 USD
$83.59 USD - $83.59 USD
$83.59 USD
Svbony SV199 1.25" ADC Atmospheric Dispersion Corrector
$79.64 USD - $79.64 USD
$79.64 USD
$79.64 USD - $79.64 USD
$79.64 USD

SVBONY SV199 ADC Atmospheric Dispersion Corrector - 1.25"

Corrects atmospheric dispersion for planetary viewing 2° to 2.5° prism deviation angle 24mm clear optical aperture Fits standard 1.25" focusers an...

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$79.64 USD - $79.64 USD
$79.64 USD
$79.64 USD - $79.64 USD
$79.64 USD
SVBONY SV209 1.0X Field Flattener for SV550 80F6
SVBONY SV209 1.0X Field Flattener for SV550 80F6
$119.99 USD - $119.99 USD
$119.99 USD
$119.99 USD - $119.99 USD
$119.99 USD

SVBONY SV209 1.0X Field Flattener for SV550 80F6

1.0x focal correction factor Designed for the Svbony SV550 80F6 telescope 45mm fully illuminated image circle M63x1 telescope-side connection Prov...

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$119.99 USD - $119.99 USD
$119.99 USD
$119.99 USD - $119.99 USD
$119.99 USD
Tele Vue 0.8x Focal Reducer 1
$403.00 USD - $403.00 USD
$403.00 USD
$403.00 USD - $403.00 USD
$403.00 USD

Tele Vue 0.8x Focal Reducer

Reduction Factor: 0.8x Optical Design: Reducer and Field Flattener Telescope Connection: 2-inch Barrel Camera Connection: M42x0.75 T-Ring Thread O...

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$403.00 USD - $403.00 USD
$403.00 USD
$403.00 USD - $403.00 USD
$403.00 USD
Tele Vue 0.8x Reducer for NP Scopes 2
Tele Vue 0.8x Reducer for NP Scopes 1
$572.00 USD - $572.00 USD
$572.00 USD
$572.00 USD - $572.00 USD
$572.00 USD

Tele Vue 0.8x Reducer for NP Scopes

Focal Length Reduction Factor: 0.8x Telescope Interface: Tele Vue 2.4" Imaging System Thread Camera Interface: Threaded for Tele Vue Wide T-Adapte...

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$572.00 USD - $572.00 USD
$572.00 USD
$572.00 USD - $572.00 USD
$572.00 USD
Tele Vue 0.8x Reducer-Flattener for 102 Scopes 2
Tele Vue 0.8x Reducer-Flattener for 102 Scopes 1
$446.00 USD - $446.00 USD
$446.00 USD
$446.00 USD - $446.00 USD
$446.00 USD

Tele Vue 0.8x Reducer-Flattener for 102 Scopes

Reduction Factor: 0.8x Effective Focal Length (on TV-102): 704mm Effective Focal Ratio (on TV-102): f/6.9 Compatibility: TV-102 and 800-1000mm f...

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$446.00 USD - $446.00 USD
$446.00 USD
$446.00 USD - $446.00 USD
$446.00 USD
Tele Vue Large Field Corrector- NP101-NP101is-NP127is 2
Tele Vue Large Field Corrector- NP101-NP101is-NP127is 1
$343.00 USD - $343.00 USD
$343.00 USD
$343.00 USD - $343.00 USD
$343.00 USD

Tele Vue Large Field Corrector- NP101-NP101is-NP127is

Corrects Field Curvature for Large Format Sensors Designed for Tele Vue NP101, NP101is, and NP127is Telescopes Recommended for 35mm (43mm Diagonal...

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$343.00 USD - $343.00 USD
$343.00 USD
$343.00 USD - $343.00 USD
$343.00 USD
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$278.00 USD
$278.00 USD - $278.00 USD
$278.00 USD
$264.10 USD
$264.10 USD - $264.10 USD
$264.10 USD

William Optics Adjustable Flat61 for Z61

1.0x Flattener Power Designed for William Optics Zenithstar 61 Full-Frame Sensor Coverage Adjustable Back Focus Mechanism M54 Telescope Thread &am...

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$278.00 USD
$278.00 USD - $278.00 USD
$278.00 USD
$264.10 USD
$264.10 USD - $264.10 USD
$264.10 USD
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$269.00 USD
$269.00 USD - $269.00 USD
$269.00 USD
$255.55 USD
$255.55 USD - $255.55 USD
$255.55 USD

William Optics Adjustable Flat6AIII

0.8x Focal Reducer & Field Flattener Optimized for GT71, GT81, Z81 & Z103 Refractors Illuminates Full-Frame Sensors Adjustable Back Focus ...

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$269.00 USD
$269.00 USD - $269.00 USD
$269.00 USD
$255.55 USD
$255.55 USD - $255.55 USD
$255.55 USD
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$348.00 USD
$348.00 USD - $348.00 USD
$348.00 USD
$330.60 USD
$330.60 USD - $330.60 USD
$330.60 USD

William Optics Adjustable Flat6AIII for FLT91

Dedicated Field Flattener for the William Optics FLT91 Telescope Corrects Field Curvature for Pinpoint Stars Edge-to-Edge Integrated Adjustment Ri...

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$348.00 USD
$348.00 USD - $348.00 USD
$348.00 USD
$330.60 USD
$330.60 USD - $330.60 USD
$330.60 USD
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$278.00 USD
$278.00 USD - $278.00 USD
$278.00 USD
$264.10 USD
$264.10 USD - $264.10 USD
$264.10 USD

William Optics Adjustable Flat73A for Z73

Designed specifically for the William Optics ZenithStar 73 APO Delivers a 1.0x, perfectly flat field across full-frame sensors Connects to the Z73...

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$278.00 USD
$278.00 USD - $278.00 USD
$278.00 USD
$264.10 USD
$264.10 USD - $264.10 USD
$264.10 USD
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$284.00 USD
$284.00 USD - $284.00 USD
$284.00 USD
$269.80 USD
$269.80 USD - $269.80 USD
$269.80 USD

William Optics Adjustable Reducer Flattener Flat61R for Z61

Adjustable reducer and field flattener for William Optics Z61 telescope Improves image sharpness and reduces distortion Description ...

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$284.00 USD
$284.00 USD - $284.00 USD
$284.00 USD
$269.80 USD
$269.80 USD - $269.80 USD
$269.80 USD
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$284.00 USD
$284.00 USD - $284.00 USD
$284.00 USD
$269.80 USD
$269.80 USD - $269.80 USD
$269.80 USD

William Optics Adjustable Reducer Flattener Flat73R for Z73

Reduces focal length by a factor of 0.8x Designed for the William Optics Zenithstar 73 telescope Provides edge-to-edge flat field for full-frame s...

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$284.00 USD
$284.00 USD - $284.00 USD
$284.00 USD
$269.80 USD
$269.80 USD - $269.80 USD
$269.80 USD
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$788.00 USD
$788.00 USD - $788.00 USD
$788.00 USD
$748.60 USD
$748.60 USD - $748.60 USD
$748.60 USD

William Optics Flattener 68III

1.0x Flattener Power preserves native focal length Corrects field curvature for Full Frame sensors Designed for William Optics FLT132, GT102, and ...

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$788.00 USD
$788.00 USD - $788.00 USD
$788.00 USD
$748.60 USD
$748.60 USD - $748.60 USD
$748.60 USD
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William Optics Ultra Flat 132 (0.79x Reducer)
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$1,068.00 USD
$1,068.00 USD - $1,068.00 USD
$1,068.00 USD
$1,014.60 USD
$1,014.60 USD - $1,014.60 USD
$1,014.60 USD

William Optics Ultra Flat 132 (0.79x Reducer)

Reduces focal ratio by a factor of 0.79x Provides a flat field for Full Frame, APS-C, and M4/3 sensors 3-element, 3-group optical design Connects ...

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$1,068.00 USD
$1,068.00 USD - $1,068.00 USD
$1,068.00 USD
$1,014.60 USD
$1,014.60 USD - $1,014.60 USD
$1,014.60 USD
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William Optics Ultra Flat 156 (0.79x Reducer)
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$1,068.00 USD
$1,068.00 USD - $1,068.00 USD
$1,068.00 USD
$1,014.60 USD
$1,014.60 USD - $1,014.60 USD
$1,014.60 USD

William Optics Ultra Flat 156 (0.79x Reducer)

Reduces focal ratio by a factor of 0.79x Designed for Medium Format, Full Frame, and APS-C sensors 3-element, 3-group optical design 75.5mm optica...

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$1,068.00 USD
$1,068.00 USD - $1,068.00 USD
$1,068.00 USD
$1,014.60 USD
$1,014.60 USD - $1,014.60 USD
$1,014.60 USD
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Flattener or Reducer?

  • 1.0x flattener: Keeps native focal length. Best for small targets and when your camera's pixel scale already suits the telescope.
  • 0.7x to 0.85x reducer-flattener: Wider field and faster focal ratio. A 0.8x reducer cuts exposure time by about a third.
  • SCT reducers: f/6.3 reducer-corrector for standard SCTs, 0.7x reducer for EdgeHD.
  • Dedicated or universal: A corrector designed for your exact telescope almost always beats a universal one, especially with larger sensors.

Getting the Back-Focus Right

Each corrector has a required distance to the sensor, often 55 mm but not always. Too short or too long and corner stars stretch. Plan the imaging train before ordering.

What We Confirm

  • Model match: We confirm which corrector the manufacturer designed for your telescope and its focuser thread.
  • Image circle: We check that the corrected field covers your sensor.
  • Spacing: We give you the full list of spacers to reach the exact distance.

Flatteners and Reducers: Frequently Asked Questions

Does my telescope need a flattener?

Doublets and triplets used with anything larger than a small sensor almost always do. Petzval and quintuplet designs have one built in.

Can I use a flattener for visual observing?

It works but adds glass and back-focus. Most observers remove it for visual use.

My corner stars are still elongated. What now?

Send us a raw image. Stars pointing toward the centre mean spacing is too short; pointing away means too long.

Which corrector fits your telescope?

Send us your telescope model and camera. We will name the corrector and the spacing.