What Is A Camera T-Ring?
A T-Ring is a simple adapter that allows you to connect your camera to a telescope or accessory to do astrophotography. On one side, it has a bayonet mount to match your specific camera, just like a lens would attach to. On the other side, it is threaded to attach to a telescope or accessory behind a telescope, which are usually T-threads or M48.
What Is A T-Adapter?
A T-Adapter is a device that adapts the telescope side connection to threads you can attach accessories to on the camera side. In most cases, you will need both a T-Adapter and a T-Ring to be able to attach your DSLR or Mirrorless camera to your telescope. A handful of telescopes, however, come with the right threads to attach a T-Ring already on the back so you don't need a T-Adapter. T-Adapters are often specific to your telescope, so be sure you get the right one.
Do I Need A T-Adapter if I Have A Focal Reducer or Other Accessory?
If you're using an optical accessory like a focal reducer, it may also have standard threads to attach a T-Ring already. To be sure, check the specifications or manual for your specific telescope/accessory you're trying to attach your camera to.
What do T-Threads (M42) and M48 (Wide) mean?
There are two main sizes of threads featured on the telescope side of T-Rings. First are T-Threads, which are 42mm in diameter, and second is M48, which is 48mm wide. You'll need to find out which size threads the telescope/accessory you're trying to attach your camera to has before deciding on a T-Ring. This is usually listed in the specifications or manual.
Technically, T-threads have M42 x 0.75 threads and pitch, whereas M42 threads are M42 x 1. However, many manufacturers often interchange the two labels, and it's generally safe to assume that T-Rings that say M42 will thread into T-threads. This size T-Ring is most common, and can accommodate up to APS-C size DSLR and Mirrorless cameras.
M48, on the other hand, is a slightly wider thread, hence why you may see the term Wide T-Ring. M48 is quickly becoming the more popular choice for thread size on telescopes and accessories as it can accommodate up to Full Frame size camera sensors without any vignetting like T-threads/M42.
What's the Difference Between Camera Mounts, and Which One Do I Have?
Each camera brand has its own proprietary bayonet mount to attach lenses (and therefore T-Rings) to. Some camera brands even have multiple mounts for different types of cameras. Thankfully, this is pretty easy to recognize, so we made this helpful chart below based on whether your camera is a DSLR or a Mirrorless camera:
||EF Mount (EF-S)
||RF Mount (Full Frame) or M Mount (APS-C)
||F Mount (FX & DX)
||X Mount (APS-C) or GF Mount (Medium Format)
||Micro 4/3 Mount
Which T-Ring Should I Get for My Camera and My Telescope?
Using the chart above, you can find which bayonet mount your DSLR or Mirrorless camera has. Then, figure out which threads are on the back of your telescope: T-threads or M48. Finally, use the filters on in the search page above to narrow down the correct T-Rings for your camera.
Do I Need To Worry About Back Focus With A T-Ring?
T-Rings are designed to provide 55mm of back focus spacing from the sensor of the camera to the telescope side of the T-Ring, so you don't usually need to worry about back focus. If your telescope or accessory requires something other than 55mm of back focus, head to our helpful back focus blog post to help you find out what you need.
What Is A Short T-Ring?
A Short T-Ring is a T-Ring that is designed to give you less than the standard 55mm of back focus spacing as mentioned above. This allows you to reach focus on short back focus setups. A Short T-Ring can also let you add accessories otherwise not possible with a normal length T-Ring, such as a filter drawer for filters if your camera cannot accommodate clip-in filters.