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Closed October 10–12 for Thanksgiving weekend
Closed October 10–12 for Thanksgiving weekend

Correctors and Reducers

Round stars in the corners are not a processing achievement — they are a spacing achievement. Field flatteners and reducers correct the curved focal plane and off-axis aberrations that every telescope has to some degree, and they only work when spaced to within about a millimetre of their design distance. David Astro carries field flatteners and reducers in Canada, shipping from Canadian stock.

This is the category where our back-focus calculation service saves the most frustration. Send us your telescope, camera and filters and we will specify the corrector and the exact spacers to go with it.

Filters

CA$271.00 - CA$328.00
CA$271.00 - CA$328.00
CA$271.00 - CA$328.00
CA$271.00

Baader MPCC Mark III (Multi Purpose Coma Corrector) - 2"

Options available
2 variants in stock

Corrects Coma in Newtonians as Fast as f/3.5 Zero Change in Focal Length or Field Size Fits Standard 2" Focusers Features Baader Planetarium Phant...

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CA$271.00 - CA$328.00
CA$271.00 - CA$328.00
CA$271.00 - CA$328.00
CA$271.00
Baader Planetarium Alan Gee Mark II Centering Ring for SC 9¼"
CA$40.00 - CA$40.00
CA$40.00
CA$40.00 - CA$40.00
CA$40.00

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

BAA-2454410

Adapts Alan Gee II Telecompressor to larger SCTs Ensures precise optical alignment Designed for Celestron 9.25" and 11" Schmidt-Cassegrain OTAs Pr...

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

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

BAA-2454405

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
CA$286.00
CA$286.00 - CA$286.00
CA$286.00
CA$277.00 - CA$277.00
CA$277.00
CA$277.00 - CA$277.00
CA$277.00

Baader RCC I Rowe Coma Corrector

BAA-2956800

Triplet optical design corrects coma in fast Newtonian telescopes Engineered for a long back focus to accommodate complex imaging trains Ideal for...

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CA$277.00 - CA$277.00
CA$277.00
CA$277.00 - CA$277.00
CA$277.00
CA$278.00 - CA$278.00
CA$278.00
CA$278.00 - CA$278.00
CA$278.00

Celestron Reducer - Corrector

CEL-94175

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$278.00 - CA$278.00
CA$278.00
CA$278.00 - CA$278.00
CA$278.00
CA$1,180.00 - CA$1,180.00
CA$1,180.00
CA$1,180.00 - CA$1,180.00
CA$1,180.00

Celestron Reducer Lens .7x - EdgeHD 1100

CEL-94241
1 in stock

Reduces EdgeHD 1100 focal ratio to f/7.7 5-element optical design with Lanthanum glass Increases field of view by 43% Maintains EdgeHD flat-field ...

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

Celestron Reducer Lens .7x - EdgeHD 1400

CEL-94240

Reduces EdgeHD 1400 focal ratio by a factor of 0.7x Custom 5-element optical design preserves flat-field imaging Provides a generous 146mm of back...

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CA$1,180.00 - CA$1,180.00
CA$1,180.00
CA$1,180.00 - CA$1,180.00
CA$1,180.00
CA$582.00 - CA$582.00
CA$582.00
CA$582.00 - CA$582.00
CA$582.00

Celestron Reducer Lens .7x - EdgeHD 800

CEL-94242

Reduces focal length by a factor of 0.7x, changing the EdgeHD 800 from f/10 to f/7 4-element optical design maintains the native flat-field perfor...

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CA$582.00 - CA$582.00
CA$582.00
CA$582.00 - CA$582.00
CA$582.00
CA$610.00 - CA$610.00
CA$610.00
CA$610.00 - CA$610.00
CA$610.00

Celestron Reducer Lens .7x - EdgeHD 925

CEL-94245
1 in stock

Reduces focal ratio by a factor of 0.7x for faster imaging 4-element design maintains the native flat-field performance of the EdgeHD 9.25" Provid...

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CA$610.00 - CA$610.00
CA$610.00
CA$610.00 - CA$610.00
CA$610.00
Sold out
CA$199.00 - CA$199.00
CA$199.00
CA$199.00 - CA$199.00
CA$199.00

David Astro 0.6x Universal Reducer - 2"

DAV-FF0.6X

55mm back focus Works with f/5 to f/7 refractors Compatible with APS-C size cameras or smaller. Accepts 2" filters Optimized for refractors with...

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CA$199.00 - CA$199.00
CA$199.00
CA$199.00 - CA$199.00
CA$199.00
Sold out
Sold out
CA$175.00 - CA$175.00
CA$175.00
CA$175.00 - CA$175.00
CA$175.00

David Astro 0.8x Universal Reducer - 2"

DAV-FF0.8X

55mm back focus Works with f/5 to f/7 refractors Compatible with APS-C size cameras or smaller. Accepts 2" filters Optimized for refractors with...

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CA$175.00 - CA$175.00
CA$175.00
CA$175.00 - CA$175.00
CA$175.00
Sold out
CA$175.00 - CA$175.00
CA$175.00
CA$175.00 - CA$175.00
CA$175.00

David Astro Universal Field Flattener - 2"

DAV-FF1.0X
Only 5 left!

55mm back focus Works with f/5 to f/7 refractors Compatible with APS-C size cameras or smaller. Accepts 2" filters Optimized for refractors with...

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CA$175.00 - CA$175.00
CA$175.00
CA$175.00 - CA$175.00
CA$175.00
Explore Scientific 0.8x Focal Reducer
CA$196.00 - CA$196.00
CA$196.00
CA$196.00 - CA$196.00
CA$196.00

Explore Scientific 0.8x Focal Reducer

ES-FR0.8x

Reduces focal length by a factor of 0.8x for wider fields of view Engineered for refractors with focal ratios from f/5 to f/7 Provides 55mm (+/- 2...

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CA$196.00 - CA$196.00
CA$196.00
CA$196.00 - CA$196.00
CA$196.00
CA$559.99 - CA$559.99
CA$559.99
CA$559.99 - CA$559.99
CA$559.99

Explore Scientific 3" Field Flattener .7x Focal Reducer

ES-FFFR507X-00

Reduces focal ratio by a factor of 0.7x for wider fields and shorter exposures Functions as a field flattener to correct edge-of-field aberrations...

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CA$559.99 - CA$559.99
CA$559.99
CA$559.99 - CA$559.99
CA$559.99
CA$629.00 - CA$629.00
CA$629.00
CA$629.00 - CA$629.00
CA$629.00

Lunt .8X Reducer/Field Flattener

LSS-CAA-RF

Reduces focal length by a factor of 0.8x Widens the photographic field of view Flattens the image field for sharp, edge-to-edge stars Optimized fo...

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CA$629.00 - CA$629.00
CA$629.00
CA$629.00 - CA$629.00
CA$629.00
Orion Optics UK AG W-C to fit SBIG STX 16803 89dia DT- 50mm BFD 4mm adj
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG W-C to fit SBIG STX 16803 89dia DT- 50mm BFD 4mm adj

OOUK-AG-W-C-SBIG-STX

4-lens ED corrector for the AG Astrograph range Machined to fit SBIG STX 16803 89dia DT- 50mm back focal distance Individually machined to order i...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne Corr to SBIG T thread using 61mm BFD with 4mm adj
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne Corr to SBIG T thread using 61mm BFD with 4mm adj

OOUK-AG-WYNNE-CORR-SBIG-T

4-lens ED corrector for the AG Astrograph range Machined to fit SBIG T thread 61mm back focal distance Individually machined to order in the UK ...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne corrector C Mount Adaptor camera needs 18mm+-3mmBFD
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne Corrector C-Mount Adapter - Camera Needs 18mm ±3mm Back Focus

OOUK-AG-WYNNE-CORRECTOR-C-MOUNT

Camera adaptor for the AG Wynne 4-lens corrector (AG Astrograph range) C Mount adaptor for the AG Wynne corrector For cameras needing 18mm (±3mm) ...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne corrector fit Atlas-70mm OAG 3.5mmBFD +-4mm
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne corrector fit Atlas-70mm OAG 3.5mmBFD +-4mm

OOUK-AG-WYNNE-CORRECTOR-ATLAS-70MM

4-lens ED corrector for the AG Astrograph range Machined to fit Atlas-70mm OAG 3.5mm back focal distance Individually machined to order in the UK ...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne Corrector for Takahashi TAK72
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne Corrector for Takahashi TAK72

OOUK-AG-WYNNE-CORRECTOR-TAK72-35MM

Custom-designed AG Wynne corrector for the Takahashi TAK72 Engineered for a 35mm back focus distance (BFD) Provides +4mm of fine adjustment for se...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne corrector to fit 2.005" FLI using 40mm BFD with 4mm adj
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne corrector to fit 2.005" FLI using 40mm BFD with 4mm adj

OOUK-AG-WYNNE-CORRECTOR-2-005

4-lens ED corrector for the AG Astrograph range Machined to fit 2.005" FLI 40mm back focal distance Individually machined to order in the UK De...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne corrector to fit 2.55" FLI using 50mm +-4mm
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne corrector to fit 2.55" FLI using 50mm +-4mm

OOUK-AG-WYNNE-CORRECTOR-2-55

4-lens ED corrector for the AG Astrograph range Machined to fit 2.55" FLI Custom back focal distance to order Individually machined to order in th...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne corrector to fit 3" FLI using 35mm BFD with 4mm adj
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne corrector to fit 3" FLI using 35mm BFD with 4mm adj

OOUK-AG-WYNNE-CORRECTOR-3-FLI

4-lens ED corrector for the AG Astrograph range Machined to fit 3" FLI 35mm back focal distance Individually machined to order in the UK Descri...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00
Orion Optics UK AG Wynne corrector to fit Atlas to 3" MOAG using 7mm BFD
CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Orion Optics UK AG Wynne corrector to fit Atlas to 3" MOAG using 7mm BFD

OOUK-AG-WYNNE-CORRECTOR-ATLAS-3

4-lens ED corrector for the AG Astrograph range Machined to fit Atlas to 3" MOAG 7mm back focal distance Individually machined to order in the UK ...

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CA$416.00 - CA$416.00
CA$416.00
CA$416.00 - CA$416.00
CA$416.00

Flatteners, Reducers and Coma Correctors

Each type solves a different optical problem, and using the wrong one degrades the field instead of correcting it.

  • Field flatteners: Correct focal plane curvature without changing focal length, so framing stays the same and only corner star shape improves.
  • Focal reducers: Flatten and shorten focal length, typically to 0.8x or 0.7x, widening the field and increasing the effective focal ratio for shorter exposures.
  • Coma correctors: For Newtonian reflectors, correcting the comet-shaped off-axis stars inherent to a parabolic mirror, essential below about f/6.
  • SCT reducer-correctors: Typically 0.63x units for Schmidt-Cassegrains, which both widen the field and considerably reduce exposure times at long focal lengths.
  • Telescope-specific versus universal: A corrector designed for your exact tube will outperform a universal one, particularly at the corners of large sensors.
  • Back-focus specification: Every corrector has a design distance from its rear surface to the sensor, commonly 55 mm. Missing it produces elongated corner stars pointing either inward or outward.

Why Choose David Astro for Field Flatteners and Reducers

A corrector is one of the few products where the accessory list matters as much as the product itself.

  • Back-focus calculated and spacers supplied: We provide the full component list including fine shims, and account for the focal shift your filter glass introduces.
  • Star shape diagnosis: If your corners are wrong, the direction of elongation tells us whether you are over- or under-spaced. Send us a corner crop and we will tell you which way to move.
  • Telescope-matched selection: We identify the corrector designed for your specific tube rather than defaulting to a universal unit that will underperform on a large sensor.
  • Authorized dealer: Genuine correctors with full manufacturer warranty, held in stock for fast domestic shipping.
  • Ships from Canada: No duties or brokerage fees for Canadian customers.

Field Flatteners and Reducers in Canada — Frequently Asked Questions

How precise does back-focus have to be?
Within about one millimetre for most correctors, and tighter at fast focal ratios. That is why filter thickness matters — a 3 mm filter shifts focus by roughly 1 mm, which is the entire tolerance.
My corner stars are elongated. Am I over or under spaced?
Stars elongated radially, pointing away from centre, generally indicate too much spacing. Tangentially elongated stars generally indicate too little. Send us a corner crop and we will confirm and give you a number.
Flattener or reducer?
Use a flattener if your framing is already right and only the corners are wrong. Use a reducer if you also want a wider field and shorter exposures, accepting that your image scale drops.
Will a universal corrector work on my telescope?
Sometimes acceptably, but a corrector matched to your specific tube will correct better at the edges, especially with an APS-C or larger sensor. Tell us your tube and we will check what exists for it.

Chasing corner stars?

Send us your imaging train and a corner crop. We will calculate the spacing and specify the parts. Held in Canada, shipped fast.