A T-Adapter means that you can attach your 35mm SLR camera to the prime focus of your telescope or spotting scope. This arrangement
...A T-Adapter means that you can attach your 35mm SLR camera to the prime focus of your telescope or spotting scope. This arrangement is used for terrestrial photography & short exposure lunar & planetary photography. It can also be used for long exposure deep-sky photography when using a separate guidescope. Both a T-Adapter & T-Ring are required to mount a 35mm SLR camera to your instrument.