What are the T-2 threads on the Baader 15mm Extension Tube?
T-2 threads are a universal standard in astronomy for connecting accessories. They consist of a metric thread with a 42mm diameter and a 0.75mm thread pitch (M42x0.75). This Baader 15mm tube has male threads on one side and female threads on the other, allowing it to be inserted anywhere in a T-2 compatible imaging train.
How does the Baader 15mm Extension Tube help with back focus on my Celestron EdgeHD with a 0.7x reducer?
Most focal reducers and flatteners require a very specific back focus distance (e.g., 55mm) from the corrector to the camera sensor for optimal performance. You use extension tubes like this 15mm Baader T-2 tube to build up that precise distance. By combining it with your camera's flange distance and other adapters, you can precisely hit the required spacing for sharp, coma-free stars corner-to-corner.
Can I stack this 15mm Baader T-2 tube with other extensions?
Yes. Baader extension tubes are designed to be modular. You can thread this 15mm tube together with other Baader T-2 extensions (e.g., 7.5mm, 40mm) or T-2 compatible accessories to achieve any required spacing. The high-quality machining ensures a secure and parallel connection when stacked.
Will this 15mm Baader extension tube cause vignetting with my full-frame camera on a fast f/4 Newtonian?
It might. The T-2 thread standard has a clear aperture of roughly 41mm. While sufficient for APS-C and smaller sensors, it can cause some light fall-off (vignetting) in the corners of a full-frame (36x24mm) sensor, especially in fast optical systems. For full-frame imaging, the larger M48 (2-inch filter) thread standard is generally recommended to avoid this issue.
What's the difference between this T-2 extension tube and a variable T-ring?
A variable T-ring allows for continuous adjustment of spacing, which can be useful for initial setup. However, fixed tubes like this 15mm Baader T-2 extension provide superior rigidity and parallelism. Once you determine the optimal spacing, using fixed tubes eliminates the risk of tilt or flex that can occur with helical or sliding variable spacers.
Why choose a Baader 15mm T-2 Extension Tube over a generic one?
Baader Planetarium is known for its precise machining and high-quality materials. A Baader tube ensures that the stated 15mm length is accurate and that the threads are cut cleanly for a secure, non-binding fit. This level of precision is critical for maintaining optical alignment in a demanding imaging setup.
