What is the main purpose of the SVBONY SV119 M48 Extension Tube kit?
The primary purpose of the SV119 kit is to achieve the precise back focus (sensor-to-corrector distance) required by optical accessories like field flatteners, coma correctors, and focal reducers. The kit includes four lengths—5mm, 10mm, 15mm, and 30mm—that can be stacked to create the exact spacing needed for sharp, aberration-free stars across your entire field of view.
How would I use the SV119 kit to get 55mm of spacing for my field flattener?
Most flatteners require 55mm of back focus. To achieve this with the SV119 kit, you would stack the 30mm, 15mm, and 10mm tubes together (30 + 15 + 10 = 55mm). This allows you to precisely match the optical design requirements of your corrector using only the components in this kit.
Are the M48x0.75 threads on the SV119 kit compatible with standard 2" filters?
Yes. The M48x0.75 thread is the standard for 2-inch astronomy filters. This means you can thread these extension tubes directly onto filter wheels, filter drawers, or camera nosepieces that accept 2" filters, making them a versatile addition to almost any imaging setup.
Can I use the SV119 extension tubes with my DSLR and a coma corrector on an f/4 Newtonian?
Absolutely. An f/4 Newtonian requires a coma corrector, which in turn needs precise spacing (often 55mm) to work correctly. You would place the appropriate combination of SV119 tubes between your M48 T-ring on your DSLR and the coma corrector to achieve that distance, ensuring sharp stars from edge to edge.
What is the benefit of the internal threading in the SV119 tubes?
The internal threads act as light baffles. They are designed to trap off-axis light that might otherwise reflect off the inner surfaces of the tubes and reach the camera sensor. This reduces internal glare and significantly improves image contrast, resulting in a darker sky background and more vibrant detail in your astrophotos.
Can I stack all four SV119 tubes together?
Yes, you can stack all four tubes (5mm + 10mm + 15mm + 30mm) to achieve a total extension of 60mm. This modularity is the key feature of the kit, providing a wide range of spacing options from 5mm to 60mm in 5mm increments.
