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Imaging Train

The imaging train is the stack of parts between the telescope's corrector and the camera sensor: adapters, spacers, a filter wheel or drawer, an off-axis guider, sometimes a rotator or tilt plate. Each part has a thickness and a thread, and together they must place the sensor at the exact distance the corrector was designed for, often within half a millimetre, and perfectly square to the optical axis.

When stars are elongated in the corners, or sharp on one side and soft on the other, the imaging train is usually the cause. This collection gathers the parts that solve it, from Baader, PrimaLuceLab, William Optics, ZWO, Player One, SVBONY, Wanderer Astro, Pegasus Astro, QHYCCD, Tele Vue and many more.

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William Optics Longer adjusting adapter for FLAT68III, FLAT7A

Connects FLAT68III & FLAT7A Flatteners to M48 Imaging Trains Provides a Fixed 45mm Optical Length Input Thread: M80 x 0.75 Output Thread: M48 ...

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William Optics M42 Adapter for Elite Drawer OAG Kit Save 6% Save %
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William Optics M42 Adapter for Elite Drawer OAG Kit

Adds an M42 x 0.75 (T2) Camera-Side Connection to the Elite Drawer OAG Connects Cameras and Accessories with M42 x 0.75 (T2) Threads Dovetail Conn...

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William Optics M48 Female to M42 Male Adapter

Connects M48 Female Threads to M42 Male Threads Adds Only 5.3mm of Optical Path Length Standard 2" Filter Thread (M48x0.75) to T-Thread (M42x0.75)...

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William Optics M48 Push-in Nosepiece for WO 2" Diagonals & UniGuide Scope

Connects M48 Threaded Accessories to 2" Push-in Focusers Female M48 Threads for 2" Filter Attachment Adds a Fixed 36 mm of Optical Length Male M48...

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William Optics M54 Camera Angle Rotator (CAA)
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William Optics M54 Camera Angle Rotator (CAA)

360° of precise framing rotation Standard M54 male and female threads Adds a minimal 30.2 mm to the optical path Securely locks orientation for lo...

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William Optics M63 Female to 2" Push-in Adapter for P-FLAT6AIII

Connects P-FLAT6AIII Flattener to 2" Focuser Female M63 Threads for Flattener Connection Male 2" Push-in Barrel for Focuser Internal M48 Female Th...

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William Optics M63(F) to M48(M) Photo Adapter

Adds 80mm of Optical Length Connects to M63 Female Threads Outputs to M48 Male T-Threads Enables Focus Without a Field Flattener Designed for Will...

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William Optics M92 to M63 Adapter for William Optics FLT91
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William Optics M92 to M63 Adapter for William Optics FLT91

Connects William Optics FLT91 Telescope to Flat6AIII Flattener Input Thread: M92 Male Output Thread: M63 Female Optical Path Length: 10.5 mm De...

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William Optics Micro 4/3 48mm T-Mount for Olympus - Black

Connects M48 Correctors to Olympus Micro 4/3 Cameras Fixed 35.6 mm Optical Length for Precise Back Focus Light-In Connection: M48 (Female) Thread ...

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William Optics Slide-Base 50mm Guiding Rings

Securely holds 50mm-class guidescopes and finders with tubes from 33 to 58 mm Slide-base design allows for fore-and-aft adjustment for precise bal...

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William Optics Slide-Base 50mm Guiding Rings - No Adjustments Screws

Seamlessly integrate with your existing astrophotography gear. Ensures stable attachment of your telescope to your mount. Description In th...

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William Optics Slide-Base UniGuide 32mm Scope

32mm Doublet Objective Lens Fast f/3.75 Focal Ratio 120mm Focal Length Integrated Vixen/Synta-Style Slide-Base Ultra-Lightweight at 0.23 kg (0.51 ...

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William Optics Slide-Base UniGuide 50mm Scope

50mm Aperture Doublet Lens 200mm Focal Length (f/4.0) Integrated 1.25" RotoLock Adapter Slide-Base for William Optics Handles Total Weight: 0.5 kg...

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William Optics STL Adapter for FLT Flattener

Connects SBIG STL-11000 Series CCD Cameras Attaches to P-FLAT68 Field Flatteners via M80 Female Thread Provides a Precise 69 mm Optical Path Lengt...

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William Optics Super High Precision COPPER T-Mount for Canon EOS Full Frame

Solid Copper Construction for Maximum Rigidity M48 (2") Female Thread for Wide-Field Correctors Connects to Canon EOS Camera Bodies Precise 10.6 m...

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William Optics Super High Precision COPPER T-Mount for Nikon Full Frame

Solid Copper Construction for Maximum Rigidity M48 x 0.75 Female Thread for Wide-Field Correctors Designed for Nikon F-Mount Full-Frame Cameras Pr...

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ZWO 30mm f/5 APO Guide Scope

30mm Aperture 150mm Focal Length (f/5.0) Triplet Apochromatic (APO) Lens Design Precise Helical Focuser Lightweight at 0.77 lb. Description FAQ...

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ZWO Adapter - 2mm M54(M)/M48(F)

Connects M54 Filter Wheels to M48 Accessories Adds Only 2 mm to Optical Path Maintains 55 mm Back Focus Standard Knurled Edge for Secure Grip Desi...

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ZWO CAA Rotator

Motorized rotation with 0.02° step resolution Adds only 16.5 mm of backfocus 48 mm clear aperture for full-frame sensors ASCOM and ASIAIR compatib...

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ZWO M42 Adapter for OAG

M42 adapter for main imaging camera Specifications

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ZWO M42 Extension - 21mm

Adds exactly 21mm of spacing to an M42 optical train M42x0.75 female threads on one side, male threads on the other Machined aluminum with a black...

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ZWO M42 Plate for CAA Rotator

Converts ZWO CAA Rotator to M42 T-Threads Maintains 55mm Backfocus Standard CAA with M42 Plate Stays at 16.5mm Ideal for ASI533, ASI2600, and Othe...

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ZWO M42-M48 Adapter - 16.5mm

Adds a precise 16.5mm of optical path length Connects male M42 (T2) threads to female M48 threads Essential for achieving standard 55mm back focus...

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ZWO M42e to M48i Extension - 22.5mm

Establishes precise 55mm back focus with specific ZWO camera/filter wheel combinations Provides exactly 22.5 mm of optical path length Connects M4...

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Parts of the Imaging Train

  • Thread adapters and spacers: Convert between M42, M48, M54, M68 and SCT threads and set the distance. See T-rings, spacers and thread adapters.
  • Off-axis guiders: Pick off a guide star in front of the sensor, eliminating flexure between guide scope and main telescope. See off-axis guiders and guide scopes.
  • Rotators: Turn the camera to frame the target without loosening anything. Motorized rotators make framing repeatable across nights.
  • Tilt adjusters: Push-pull plates that square the sensor to the light path. See rotators and tilt adjusters.

Back-Focus in Practice

  • Start with the number: Most flatteners need 55 mm from their thread to the sensor. Some need 56.2, 63 or something else entirely. Check your corrector.
  • Count everything: Camera internal distance, filter wheel or drawer, OAG, adapters and spacers.
  • Add for filters: A filter adds about one third of its thickness. A 2 mm filter needs about 0.7 mm more spacing.
  • Prefer threads to compression: Threaded connections hold squareness much better than 2-inch nosepieces with thumb screws.

We Plan Your Train for You

  • Spacing sheet: Send us your corrector, camera and accessories. We return the list of parts and the exact distances.
  • Diagnosis: Send a raw frame and we will tell you whether the spacing is too long, too short or tilted.

Imaging Train: Frequently Asked Questions

How do I know if my back-focus is wrong?

Stars stretched radially in all corners point to spacing too short or too long. Stars that are good on one side only point to tilt.

Can I use a 2-inch nosepiece for imaging?

It works, but threaded connections are stiffer and more square. For larger sensors, go threaded.

Need a back-focus plan?

Send us your telescope, corrector and camera. We will list every part and distance.