The Nikon FSA-L1 Digital SLR Camera Adapter allows photography with Nikon F-mount digital SLR cameras and the line of Nikon Fieldscopes, but can also be used with film-based Nikon F-mount SLR cameras. It is not used in conjunction with an eyepiece, but rather you remove the eyepiece and attach this device where the eyepiece would normally attach to the Fieldscope. You then attach you F-mount camera to the other end of this device, and you're ready to shoot.
Although this adapter is recommended for use with the Nikon digital SLR cameras, it can be used with the F6, F5, F100, FM10, FE10, F65/N65 and F55/N55 cameras as well. It is not recommended for use with the F75/N75, F80/N80 & FM3a cameras because you must determine exposure yourself and what a handheld meter may tell you does not necessarily correlate to the accurate exposure for this combination.
All ventures in the world of telescope photography require the use of a sturdy tripod, first and foremost. You must take great care to keep vibrations during exposure to an absolute minimum. Employing a cable release, electronic release or remote control for tripping the shutter is absolutely necessary. And while it is not necessary per se, a mounting bracket will do wonders to reduce vibrations of your rig.