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William Optics 48mm T-Mount for Canon EOS R Mirrorless
The William Optics 48mm T-Mount for Canon EOS R Mirrorless provides a rigid, wide-aperture connection from your telescope's M48-threaded corrector. Consuming exactly 34.4 mm of optical path, it works seamlessly with your camera body to achieve the standard 55 mm back focus for flat-field astrophotography.
M48 Threads: Full-Frame Illumination for Canon R-Series Sensors
This T-Mount features a female M48x0.75 thread, which provides a significantly larger clear aperture than the older M42 T-ring standard. This wider opening is essential for illuminating the large full-frame and APS-C sensors in modern Canon R-series cameras, preventing the mechanical vignetting that can darken the corners of your images.
By connecting directly to the wide-format flatteners, reducers, and correctors common on high-end imaging refractors, this adapter ensures that the maximum amount of corrected light reaches your sensor. The result is a more evenly illuminated field, reducing the need for aggressive flat-frame correction in post-processing.
Achieving Correct Back Focus: Built for Standard 55mm Back Focus
Every field flattener or reducer requires a precise distance to the camera sensor to deliver sharp, coma-free stars across the entire frame. This William Optics T-Mount is engineered with an exact optical length of 34.4 mm, which combines with the Canon RF mount's 20.6 mm flange distance to achieve the standard 55 mm total back focus directly—no additional spacers required.
By delivering the exact 55 mm optical path out of the box, this adapter removes the guesswork and ensures your entire imaging system is performing at its peak optical potential.
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What is the advantage of this William Optics M48 T-Mount over a standard M42 T-ring for my Canon EOS R?
The primary advantage is the larger M48 (48mm) thread diameter compared to the 42mm diameter of a standard T-ring. This wider aperture prevents the adapter itself from clipping the light cone, which causes vignetting (darkened corners) on large sensors like those in Canon R-series cameras.
How does the 34.4mm optical length of the William Optics T-Mount achieve 55mm back focus?
When combined with the Canon EOS R camera body (which has a 20.6mm sensor flange distance), the adapter's 34.4mm optical length brings the total system distance to exactly 55mm (34.4mm + 20.6mm = 55mm) directly from your M48-threaded corrector without requiring additional spacers.
Is this William Optics T-Mount compatible with Canon EF or EF-S DSLR cameras?
No. This T-Mount is designed specifically for the Canon RF mount used on Canon EOS R-series mirrorless cameras (R, Ra, R3, R5, R6, etc.). It will not physically attach to Canon DSLRs that use the EF or EF-S mount.
Does the William Optics M48 T-Mount for Canon R accept 2-inch filters?
This adapter itself does not have threads to mount a filter inside it. However, its M48 female thread is designed to connect to a filter wheel, filter drawer, or corrector that accepts standard 2-inch (M48) filters.
Will this 34.4mm T-Mount work with a Celestron EdgeHD 8" and its 0.7x reducer?
Yes, but you will need additional extension. The Celestron 0.7x reducer for the EdgeHD 8" requires 146mm of back focus. Since this adapter and your camera total 55mm, you would need an additional 91mm of M48 extension tubes between the reducer and this T-Mount to reach the required distance.
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| Telescope Side Connection |
M48 (Female) |
| Camera Side Connection |
Canon EOS R Mount |
| Optical Length |
34.4 mm |
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William Optics 48mm T-Mount for Canon EOS R Mirrorless
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William Optics 2-Year Warranty
