What is the primary use for the Baader 7.5 mm M48 Extension Tube?
Its primary use is for back focus adjustment in an astrophotography imaging train. Optical correctors (like field flatteners or coma correctors) require a precise distance to the camera sensor to work correctly. This 7.5 mm tube helps you achieve that exact distance when other components don't add up perfectly.
How do I know if I need a 7.5 mm M48 tube for my setup?
You need to calculate the total back focus of your current imaging train. Start with the required back focus of your flattener/reducer (e.g., 55 mm). Then, add up the optical path length of every component after it: your off-axis guider, filter wheel, and the camera's sensor flange distance. If the total is, for example, 47.5 mm, this 7.5 mm extension tube will provide the exact spacing needed to reach 55 mm.
Can I stack this 7.5 mm M48 Extension Tube with other extensions?
Yes, absolutely. These tubes are designed to be stacked to create custom lengths. For maximum rigidity, it is always best to use a single extension of the correct length if possible. However, stacking a few high-quality tubes like this Baader extension is a common and effective practice for achieving precise spacing.
Will adding the M48 Extension Tube – 7.5 mm cause vignetting?
Because it uses the large M48 (2-inch) thread standard, this extension tube is designed to prevent vignetting on sensors up to full-frame (35mm) format. Vignetting is more likely to be caused by other components in the optical train, such as a smaller T-2 (M42) threaded item, rather than this M48 extension.
How can the 7.5 mm M48 tube help with a Baader MPCC Mark III on a Newtonian?
The Baader MPCC Mark III coma corrector requires a nominal back focus of 55 mm. If you are using a DSLR with a standard 44 mm flange distance and a 10 mm T-ring, you are already at 54 mm. A 1 mm M48 tuning ring would be ideal. However, if you are using a dedicated astronomy camera with a shorter back focus, like a ZWO camera with a 17.5 mm flange distance, you will need to add spacers. This 7.5 mm tube can be part of the combination of extensions needed to build up the remaining 37.5 mm distance.
I have a Celestron EdgeHD with a 0.7x reducer. How would this 7.5 mm M48 tube be useful?
The Celestron 0.7x reducer for EdgeHD scopes requires a very generous 146 mm of back focus. This distance must accommodate an off-axis guider, filter wheel, and camera. The 7.5 mm M48 tube is perfect for the final fine-tuning stage. After you've assembled your main components and larger extensions, you can use this smaller tube to precisely dial in the last few millimeters to hit that 146 mm target perfectly.
