Lumicon · 2" Thread-In Extension
Adds 2" of back-focus so your eyepiece or camera can reach sharp focus.
The Lumicon 2" diameter × 2" length Thread-In Eyepiece Extension Tube threads into a 2" eyepiece to add up to 2" of focus extension. A compact spacer for fine-tuning where your eyepiece sits in the focal path. The larger 2" clear aperture suits wide-field eyepieces and large-sensor imaging, where it reduces vignetting compared with a 1.25" light path.
Specifications
Barrel diameter
2"
Extension length
2"
Attachment
Thread-in — threads into a 2" eyepiece
Filter threads
2" / 48mm
When you need it
Extra back-focus is commonly required for short-range terrestrial viewing, or when you add a field flattener, focal reducer, or coma corrector to the optical train. It’s also useful for reaching focus with a camera at prime focus on short refractors, where the sensor would otherwise sit too close to the focal plane. This tube moves your eyepiece, camera, or accessory outward so the focal plane lands where it should.
In-focus travel: like any extension or spacer, this tube requires additional in-focus travel. Depending on your telescope’s focuser range, some eyepiece and accessory combinations may not reach focus — a function of the scope’s mechanical design, not the tube.
Frequently Asked Questions
What’s the difference between a thread-in and a drop-in extension tube?
A thread-in tube screws into the filter threads of your eyepiece for a fixed extension. A drop-in tube seats inside the focuser or diagonal and accepts an eyepiece on top, pushing the eyepiece back by roughly the length of the tube.
Will this fit my eyepieces and accessories?
It works with the 2" astronomy barrel standard — the larger 2-inch format used by most wide-field eyepieces and large-sensor imaging trains.
Can I use this to reach focus with a camera at prime focus?
Yes. Short refractors often can’t bring a camera to focus at prime focus because the sensor sits too close to the focal plane. An extension adds the spacing needed to reach focus, as long as your focuser has the travel to accommodate it.
Building out your focuser setup?
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