How do I use the PrimaLuceLab 9mm M48 Extension to correct my back focus?
You insert the PrimaLuceLab 9mm M48 Extension between your camera and your field flattener or reducer. Most correctors require a specific distance (often 55mm) to the sensor. This extension helps make up part of that distance. You may need to combine it with other spacers to achieve the exact measurement required by your specific optical setup.
Can I stack multiple 9mm M48 extensions together?
Yes. The PrimaLuceLab extensions are designed to be screwed together. For example, you could stack two 9mm M48 extensions to create 18mm of spacing. For finer adjustments, PrimaLuceLab also offers 0.5mm and 1mm spacers that can be placed between extensions.
My flattener requires 55mm of back focus and my camera has 17.5mm. How would the PrimaLuceLab 9mm M48 Extension fit in?
In this scenario, you need to add 37.5mm of spacing (55mm - 17.5mm = 37.5mm). The PrimaLuceLab 9mm M48 Extension can be one component of your solution. You could combine it with other extensions, such as a 20mm, a 5mm, and a few fine-tuning spacers (like three 1mm and one 0.5mm spacer) to build the required 37.5mm distance.
I'm adding an M48 filter drawer to my imaging train with an f/5 refractor. How does the 9mm M48 Extension help?
A filter drawer adds to your back focus distance, typically around 20mm. If adding the drawer pushes your sensor too far back, you may need to replace a longer extension with a shorter one. The PrimaLuceLab 9mm M48 Extension is a useful component to have on hand to make these kinds of adjustments, helping you re-establish the correct total spacing after introducing a new accessory.
What makes the knurled grip on the PrimaLuceLab 9mm M48 Extension useful?
The knurled grip provides a textured surface that is much easier to hold and turn than a smooth cylinder, especially in cold or damp conditions when you might be wearing gloves. It prevents the frustration of trying to unscrew a tightly threaded, slippery component in the dark.
Why is the internal black anodizing important on the PrimaLuceLab 9mm M48 Extension?
The internal black anodizing is a critical anti-reflection measure. Bright stars outside the field of view can send light into the optical tube at an angle. A reflective inner surface on an extension tube could bounce this stray light onto your camera sensor, reducing contrast and creating artifacts. The matte black finish absorbs this light, preserving the dark background of your images.
