Why do I need the Baader UFC S70 5mm Extension for my HyperStar setup?
HyperStar systems operate at very fast focal ratios (around f/2), which creates a very small tolerance for back focus errors—often just +/- 0.3mm. The Baader UFC S70 5mm Extension allows you to add a precise, known amount of spacing to your imaging train to compensate for the optical path length of your camera, filter slider, and filters, ensuring you can hit that critical distance for sharp stars.
How does a filter affect the back focus calculation with the Baader UFC S70 5mm Extension?
When light passes through a glass filter, it is refracted, which effectively increases the optical path length. To compensate, you must physically move the sensor further away from the optics. A common rule is that the required extension is approximately one-third of the filter's thickness. For a standard 2mm thick filter, you would need to add about 0.67mm of physical spacing, which this 5mm extension helps to achieve in combination with other UFC adapters.
What is the S70 dovetail on the Baader UFC S70 5mm Extension?
The S70 refers to Baader's proprietary 70mm dovetail standard. It provides a wide, secure, and non-flexing connection that is superior to standard threading. It prevents tilt in the imaging train, which is a common problem with heavy cameras and accessories attached via smaller M42 or M48 threads.
Can I stack multiple Baader UFC S70 5mm Extensions?
Yes, the Baader UFC system is modular. You can stack multiple extensions if needed. For example, using two of these would provide 10mm of spacing. However, for longer distances, it is generally better to use a single, longer extension (like a 15mm) if available to maximize rigidity.
Is the Baader UFC S70 5mm Extension only for HyperStar systems?
No, while it is essential for the tight tolerances of HyperStar, this 5mm extension is a universal part of the Baader UFC system. It can be used in any optical train where you need to precisely add 5mm of spacing using the S70 dovetail standard, such as with Takahashi or other high-end refractor focusers adapted for the UFC system.
Will the Baader UFC S70 5mm Extension work on my Celestron RASA telescope?
Yes. The Celestron RASA (Rowe-Ackermann Schmidt Astrograph) is another fast optical design with critical back focus requirements, similar to HyperStar. The Baader UFC system, including the 5mm S70 Extension, is an excellent choice for building a rigid, tilt-free imaging train for RASA telescopes to achieve precise spacing for your specific camera and filters.
