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Correcteurs et réducteurs

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.

Filtres

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

Askar 0,6x Réducteur pour 103APO

ASK-ASKRE10306
1 en stock

Optimisé pour l'Askar 103APO Description L'Askar 103 APO propose trois accessoires premium en option : un aplatisseur 1,0x, u...

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

Askar 0.75x 71F Reducer

ASK-ASKAR71R

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
CA$291.00
CA$291.00 - CA$291.00
CA$291.00
CA$368.00 - CA$368.00
CA$368.00
CA$368.00 - CA$368.00
CA$368.00

Réducteur Askar 0.76x pour 80PHQ

ASK-ASKAR80R

Optimisé pour l'Askar 80PHQ Description Le nouveau réducteur plein format Askar de 3 pouces 0,76x, conçu spécifiquement pour ...

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CA$368.00 - CA$368.00
CA$368.00
CA$368.00 - CA$368.00
CA$368.00
CA$538.00 - CA$538.00
CA$538.00
CA$538.00 - CA$538.00
CA$538.00

Réducteur universel Askar 0,7x pour 107PHQ/130PHQ/151PHQ

ASK-ASF107130RE

Optimisé pour l'Askar 107PHQ/130PHQ/151PHQ Description Le nouveau réducteur plein format 3" 0,7x d'Askar est conçu pour les a...

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

Askar 0,8x Réducteur pour 103APO

ASK-ASKRE10308

Optimisé pour l'Askar 103 APO Description Caractéristiques L'Askar 103 APO propose trois accessoires premium en option : un ...

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

Askar 0.8x Reducer for 120APO

ASK-ASKRE12008

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

ASK-ASAPO111R

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
CA$419.00
CA$419.00 - CA$419.00
CA$419.00
CA$2,099.00 - CA$2,099.00
CA$2,099.00
CA$2,099.00 - CA$2,099.00
CA$2,099.00

Askar 111F Flat-Field Astrograph

ASK-ASKAR111F
1 en stock

111mm Aperture Quadruplet APO Optics 766mm Focal Length at f/6.9 44mm Full-Frame Corrected Image Circle Integrated Field Flattener Design 5.74kg N...

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CA$2,099.00 - CA$2,099.00
CA$2,099.00
CA$2,099.00 - CA$2,099.00
CA$2,099.00
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

ASK-ASKAR131FRD

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

ASK-ASKRE18508
1 en stock

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

Askar 185APO 1x Full-frame Flattener

ASK-ASKFL18510

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$460.00 - CA$460.00
CA$460.00
CA$460.00 - CA$460.00
CA$460.00
CA$307.00 - CA$307.00
CA$307.00
CA$307.00 - CA$307.00
CA$307.00

Askar 1x aplatisseur de champ pour 103APO

ASK-ASKFL10310
1 en stock

Corrige la courbure du champ et le coma Usiné CNC dans l'ensemble Le poids total est de 0,58 kg. Description L'apl...

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

Askar 1x Field Flattener for 120APO

ASK-ASKFL12010
1 en stock

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
CA$306.00
CA$306.00 - CA$306.00
CA$306.00
CA$384.00 - CA$384.00
CA$384.00
CA$384.00 - CA$384.00
CA$384.00

Réducteur plein format Askar 2,5" F/3,9 pour FRA400 et FRA500

ASK-ASKAR7256RD
2 en stock

Réducteur de focale de 2,5" conçu pour les télescopes Askar FRA400 et FRA500 Réduit le rapport focal à f/3,9, optimisé pour les capteurs ...

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CA$384.00 - CA$384.00
CA$384.00
CA$384.00 - CA$384.00
CA$384.00
CA$615.00 - CA$615.00
CA$615.00
CA$615.00 - CA$615.00
CA$615.00

Réducteur plein cadre Askar 3" F/3.9 pour FRA600

ASK-ASKAR656RD

Réducteur de focale 3" conçu spécifiquement pour le télescope Askar FRA600 Réduit le rapport focal à f/3,9, optimisé pour les capteurs pl...

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CA$615.00 - CA$615.00
CA$615.00
CA$615.00 - CA$615.00
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

ASK-ASKAR60R

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

ASK-ASKAR91R

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

Baader Télécompresseur Alan Gee Mark II

BAA-2454400

Une limitation courante qui afflige les propriétaires des télescopes Schmidt-Cassegrain les plus populaires est la taille de champ étroite et les g...

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CA$401.00 - CA$401.00
CA$401.00
CA$401.00 - CA$401.00
CA$401.00
CA$1,063.00 - CA$1,063.00
CA$1,063.00
CA$1,063.00 - CA$1,063.00
CA$1,063.00

Baader Convertisseur Fluorite Flatfield

BAA-2458200

Système de lentilles en fluorite apochromatique multicouches Résolution de ligne 10 fois supérieure à celle des meilleurs oculaires de projectio...

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CA$1,063.00 - CA$1,063.00
CA$1,063.00
CA$1,063.00 - CA$1,063.00
CA$1,063.00
CA$1,056.00 - CA$1,056.00
CA$1,056.00
CA$1,056.00 - CA$1,056.00
CA$1,056.00

Baader Aplanisseur de champ M68

BAA-2458260

Correcteur de champ à 3 lentilles pour BAADER APO 95/560 CaF2 Travel Companion Backfocus de 76,11 mm, champ de vision corrigé de 52 mm Filetage...

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CA$1,056.00 - CA$1,056.00
CA$1,056.00
CA$1,056.00 - CA$1,056.00
CA$1,056.00
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 (Correcteur de Coma Polyvalent) - 2"

Options available
2 variants in stock

Correcteur de coma pour télescopes Newton, qui ne réduit ni la distance focale ni le champ image de votre télescope Grands objectifs pour des ex...

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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 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
Baader Planetarium Glasspathcorrector 2" / 1.7x for Newtons
CA$316.00 - CA$316.00
CA$316.00
CA$316.00 - CA$316.00
CA$316.00

Baader Planetarium Glasspathcorrector 2" / 1.7x for Newtons

BAA-2456300

1.7x focal length multiplier Enables binoviewer use in Newtonian telescopes Integrated coma corrector for sharp edge-of-field stars Designed for 2...

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CA$316.00 - CA$316.00
CA$316.00
CA$316.00 - CA$316.00
CA$316.00
CA$277.00 - CA$277.00
CA$277.00
CA$277.00 - CA$277.00
CA$277.00

Baader Correcteur de Coma RCC I Rowe

BAA-2956800

Le RCC I (Rowe Coma Corrector) est un correcteur de coma de Dave Rowe avec un design Triplet Lense pour f/4 Newtons Le RCC fonctionne de f/3.5 à...

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

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.