This Celestron T-adapter for Nexstar 4, C40 and C90 is used to screw a single reflex camera -fitted with a T-thread adapter- onto the telescope tube, enabling you to take photographs in the primary focal point (without eyepiece). Your telescope acts a telelens. It is possible to photograph with eyepiece, though. This is called eyepiece projection. Please take into account that the shutter time increases dramatically.
Longer and shorter shutter times
This Celestron T-adapter enables you to attach your 35mm single reflex camera to the primary focus of your telescope or spotting scope. This is used for photography with shorter shutter times, such as terrestrial photography and photography of the moon and planets. This type of photography can also be used with longer shutter times and deep-sky photography when using a separate finder. Both a T adapter and a T ring are to be used to mount a 35mm digital single reflex camera onto your optical instrument.