This celestron t adapter is for the celestron edgehd 924 1100 and 1400 schmidt cassegrain telescopes simply screws onto the rear cell it then allows you to attach your dslr camera to the prime focus of your telescope with this arrangement it can be used for terrestrial and short exposure lunar and planetary photography with the addition of a guide scope it can also be used for long exposure deep sky photography requires the use of a t ring to suit your camera type