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Dial In Perfect Back Focus with Tele Vue Accessory Tubes
The Tele Vue Set of 2 (TLF+TLG) 2.4" Accessory Tubes provides the ultra-fine spacing adjustments required to achieve critical back focus for astrophotography. This set, containing 1mm and 2mm threaded spacers, is an essential tool for imagers using Tele Vue NP-series telescopes to eliminate field curvature and achieve perfectly sharp stars from corner to corner.
The Final Millimeters of Imaging Precision
Modern field flatteners and reducers are designed with a very specific back focus distance, the spacing between the corrector lens and the camera sensor. Deviating from this distance by even a small amount can introduce star elongation and other aberrations, particularly at the edges of your image frame. This set allows you to bridge the final gap in your imaging train with precision.
When your standard adapters and spacers get you close but not exactly to the prescribed 55mm or other target distance, these tubes are the solution. The 1mm and 2mm increments, used individually or together, provide the granular control needed to methodically test and lock in the optimal spacing for your specific camera and filter wheel combination.
The TLF-0040 (1mm) Fine-Tuning Spacer
The 1mm tube is your tool for the most delicate adjustments. When you have analyzed an image and see only slight stellar elongation in the corners, this spacer is often the exact amount of correction needed. Its minimal length allows you to incrementally walk the sensor plane into the perfect focal point without overshooting the mark.
This is particularly valuable when you introduce new components like a filter slide or off-axis guider that slightly alter your optical path length. The TLF-0040 provides a calibrated, repeatable way to compensate for these changes, saving you the frustration of trial-and-error with less precise shims or variable spacers.
The TLG-0080 (2mm) Coarse Adjustment Spacer
The 2mm tube serves as a foundational building block in your spacing toolkit. It is the perfect first step when you know your current setup is short by a few millimeters. Combining it with the 1mm tube gives you a 3mm option, expanding your adjustment range without needing to buy a separate spacer.
For imagers using DSLRs or mirrorless cameras with T-rings of non-standard thicknesses, the TLG-0080 is often the key to getting into the correct back focus zone. It provides a solid, measured starting point for further fine-tuning, ensuring your entire imaging train remains rigid and aligned.
Rigid, Zero-Flexure 2.4" Threaded Connections
Unlike slip-fit or compression ring connections, the Tele Vue 2.4" threaded interface on these tubes guarantees perfect coaxial alignment. Once screwed into your NP101is, NP127is, or other Imaging System components, they become a rigid extension of the optical tube. This eliminates any possibility of tilt, which is a primary cause of misshapen stars in one corner of an image.
The security of a threaded connection means you can assemble your entire camera train, from reducer to filter wheel to camera, without worrying about sag or misalignment as the telescope tracks across the sky. This mechanical stability is the bedrock of a successful imaging session, ensuring that your optical corrections perform exactly as designed.
Contrast-Preserving Internal Blackening
The interior of each accessory tube is treated with a matte black, anti-reflective finish. This surface is designed to trap any stray light that might enter the optical path from off-axis sources. By preventing this light from reflecting off internal surfaces and reaching the sensor, the tubes help preserve the deep, dark backgrounds and high contrast of your final images.
This is not merely a cosmetic feature. In long-exposure astrophotography, even faint internal reflections can build up over time, reducing the signal-to-noise ratio and washing out faint nebulosity. The meticulous internal finishing of these tubes is a small but critical detail that contributes to a cleaner, more professional final result.
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What problem do these Tele Vue accessory tubes solve?
They provide precise, small spacing adjustments (1mm and 2mm) needed to achieve the exact back focus distance required by your field flattener or reducer. This is critical for correcting star shape at the edge of your images.
Are these tubes compatible with 2-inch accessories?
No, these are specifically for the Tele Vue Imaging System, which uses a larger 2.4-inch diameter threaded connection. They will not thread into standard 2-inch focusers, diagonals, or filters.
Can I stack the 1mm and 2mm tubes together?
Yes. The tubes are designed to be threaded together, allowing you to create a rigid 3mm spacer if needed. This gives you three spacing options (1mm, 2mm, 3mm) from just two components.
Why use these instead of a variable spacer?
Fixed, threaded tubes like these offer superior rigidity and guaranteed alignment. Variable spacers can sometimes introduce a small amount of tilt into the imaging train, which can be difficult to diagnose. These tubes eliminate that possibility.
Which Tele Vue telescopes use the 2.4" accessory tubes?
These are primarily used with Tele Vue's "is" series refractors, such as the NP101is and NP127is, which feature the large 2.4-inch Imaging System focuser for wide-field astrophotography.
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| Product Code |
TLS-2245 (Set), TLF-0040 (1mm), TLG-0080 (2mm) |
| Accessory Type |
Threaded Extension Tube |
| Extension Length |
1mm (0.040") and 2mm (0.080") |
| Connection Diameter |
2.4 inches |
| Thread Pitch |
Proprietary Tele Vue Imaging System Thread |
| Material |
Black Anodized Aluminum |
| Compatibility |
Tele Vue NP101is, NP127is, and other 2.4" Imaging System components |
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1mm (0.040") Accessory Tube (TLF-0040)
× 1
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2mm (0.080") Accessory Tube (TLG-0080)
× 1
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Tele Vue 5-Year Limited Warranty
