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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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CA$461.00 - CA$461.00
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Askar 0.6x Reducer for 103APO

Transforms Askar 103APO to an f/4.08, 420.24mm focal length system Quadruplet optical design provides field flattening for full-frame sensors Stan...

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CA$461.00 - CA$461.00
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CA$461.00
CA$291.00 - CA$291.00
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CA$291.00 - CA$291.00
CA$291.00

Askar 0.75x 71F Reducer

0.75x Reduction Factor Transforms Askar 71F to f/5.2 New Focal Length: 369mm Standard 55mm Back Focus Triplet Optical Design Description FAQ Sp...

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CA$291.00 - CA$291.00
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CA$368.00 - CA$368.00
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Askar 0.76x Reducer for 80PHQ

0.76x reduction factor specifically for the Askar 80PHQ Reduces focal ratio from f/7.5 to a faster f/5.7 Creates a new focal length of 456mm Gener...

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CA$368.00 - CA$368.00
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CA$538.00 - CA$538.00
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Askar 0.7x Universal Reducer for 107PHQ/130PHQ/151PHQ

0.7x Focal Reduction Factor 44mm Full-Frame Image Circle Maintains a Standard 55mm Backfocus 3-Element Air-Spaced Design with ED Glass Optimized f...

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CA$538.00 - CA$538.00
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CA$307.00 - CA$307.00
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CA$307.00

Askar 0.8x Reducer for 103APO

Reduces telescope focal ratio to a faster f/5.44 Shortens 103APO focal length to 560.32mm for wider fields Triplet optical design provides field f...

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Askar 0.8x Reducer for 120APO

Reduces Askar 120APO to a fast f/5.6 focal ratio Shortens focal length to 672mm for wider fields of view Triplet optical design provides field fla...

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CA$306.00 - CA$306.00
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CA$461.00 - CA$461.00
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Askar 0.8x Reducer for 140APO

Reduces 140APO Focal Ratio to f/5.6 Shortens 140APO Focal Length to 784mm Standard 55mm Back Focus Requirement Triplet Optical Design with Field F...

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CA$461.00 - CA$461.00
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CA$461.00
Askar 111F 0.74× Reducer
CA$419.00 - CA$419.00
CA$419.00
CA$419.00 - CA$419.00
CA$419.00

Askar 111F 0.74× Reducer

Reduces Telescope Focal Ratio to f/5.1 Creates a 566mm Focal Length Imaging System Triplet Optical Design for Field Flattening Provides Standard 5...

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CA$419.00 - CA$419.00
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CA$419.00
Askar 131F 0.74× Reducer
CA$419.00 - CA$419.00
CA$419.00
CA$419.00 - CA$419.00
CA$419.00

Askar 131F 0.74× Reducer

Reduces telescope focal ratio to f/5.6 Achieves a 733.6mm final focal length Triplet optical design for field flattening Standard 55mm back focus ...

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CA$419.00 - CA$419.00
CA$419.00
CA$419.00 - CA$419.00
CA$419.00
Askar 185APO 0.8x Full-frame Reducer
CA$460.00 - CA$460.00
CA$460.00
CA$460.00 - CA$460.00
CA$460.00

Askar 185APO 0.8x Full-frame Reducer

Reduces Askar 185APO to f/5.6 Resulting Focal Length: 1036mm 4-Element Quadruplet Optical Design Standard 55mm Back Focus Illuminates Full-Frame S...

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CA$460.00 - CA$460.00
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CA$460.00
Askar 185APO 1x Full-frame Flattener
CA$460.00 - CA$460.00
CA$460.00
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CA$460.00

Askar 185APO 1x Full-frame Flattener

Maintains Native f/7 Focal Ratio Maintains Native 1295mm Focal Length Triplet Optical Design Standard 55mm Back Focus Includes M68, M54 & M48 ...

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CA$307.00 - CA$307.00
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CA$307.00

Askar 1x Field Flattener for 103APO

Corrects field curvature and coma for the Askar 103APO Maintains the native 700.4mm focal length and f/6.8 ratio Triplet optical design delivers s...

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CA$307.00 - CA$307.00
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CA$306.00 - CA$306.00
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CA$306.00 - CA$306.00
CA$306.00

Askar 1x Field Flattener for 120APO

Designed specifically for the Askar 120APO Telescope 1x Magnification Factor Triplet Optical Design Maintains Native f/7 Focal Ratio Standard 55mm...

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CA$306.00 - CA$306.00
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CA$461.00 - CA$461.00
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Askar 1x Field Flattener for 140APO

Engineered for the Askar 140APO Triplet Refractor 1x Flattener Preserves Native f/7 Focal Ratio Corrects a 44mm Full-Frame Image Circle Standard 5...

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CA$461.00 - CA$461.00
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CA$384.00 - CA$384.00
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Askar 2.5" F/3.9 Full Frame Reducer for FRA400 and FRA500

Reduces focal ratio to a fast f/3.9 0.7x reduction factor 44mm image circle fully illuminates full-frame sensors Standard 55mm back focus for easy...

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CA$615.00 - CA$615.00
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Askar 3" F/3.9 Full Frame Reducer for FRA600

Reduces FRA600 focal ratio to F/3.9 Designed for full-frame sensors Maintains a standard 55mm backfocus Features integrated M48 (2-inch) filter th...

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CA$615.00 - CA$615.00
CA$615.00
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CA$615.00
Askar 60F 0.75x Reducer
CA$279.00 - CA$279.00
CA$279.00
CA$279.00 - CA$279.00
CA$279.00

Askar 60F 0.75x Reducer

0.75x Focal Reduction Reduces Focal Length to 311mm Creates a Fast f/5.1 Focal Ratio 44mm Full-Frame Image Circle Standard 55mm Back Focus Triplet...

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CA$279.00 - CA$279.00
CA$279.00
CA$279.00 - CA$279.00
CA$279.00
Askar 91F 0.75x Reducer
CA$279.00 - CA$279.00
CA$279.00
CA$279.00 - CA$279.00
CA$279.00

Askar 91F 0.75x Reducer

Reduces focal ratio to a fast f/5 0.75x reduction factor for wider fields of view Triplet optical design provides field-flattening correction Stan...

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CA$279.00 - CA$279.00
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CA$279.00
CA$401.00 - CA$401.00
CA$401.00
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CA$401.00

Baader Alan Gee Telecompressor Mark II

Dramatically widens the field of view of Schmidt-Cassegrain telescopes Engineered to produce a sharp, flat field for visual and photographic use C...

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CA$401.00 - CA$401.00
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CA$1,056.00 - CA$1,056.00
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CA$1,056.00

Baader M68 Field Flattener

Corrects field curvature for astrophotography Designed for Baader APO 95/560 Travel Companion Features large M68 threads for a secure, wide-apert...

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CA$1,056.00 - CA$1,056.00
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CA$1,056.00
Baader Planetarium Alan Gee Mark II Centering Ring for SC 9¼"
CA$40.00 - CA$40.00
CA$40.00
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CA$40.00

Baader Planetarium Alan Gee Mark II Centering Ring for SC 9.25"

Adapts Alan Gee II Telecompressor to larger SCTs Ensures precise optical alignment Designed for the Celestron 9.25" Schmidt-Cassegrain OTA Prevent...

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CA$40.00 - CA$40.00
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CA$40.00
Baader Planetarium Alan Gee Universal 2" Telecompressor (UAG II)
CA$286.00 - CA$286.00
CA$286.00
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CA$286.00

Baader Planetarium Alan Gee Universal 2" Telecompressor (UAG II)

Unique telecompressor designed for visual use with binoviewers Based on the flat-field Alan Gee design by Roland Christen of AstroPhysics Enables ...

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CA$286.00 - CA$286.00
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CA$286.00
CA$278.00 - CA$278.00
CA$278.00
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CA$278.00

Celestron Reducer - Corrector

Reduces telescope focal length by 37% Converts f/10 SCTs to f/6.3 and f/11 systems to f/7 Compatible with Celestron C5, C6, C8, C9.25, C11, and C1...

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CA$1,180.00 - CA$1,180.00
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CA$1,180.00

Celestron Reducer Lens .7x - EdgeHD 1100

Reduces EdgeHD 1100 focal ratio to f/7 5-element optical design with Lanthanum glass Increases field of view by 43% Maintains EdgeHD flat-field im...

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CA$1,180.00 - CA$1,180.00
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CA$1,180.00

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.