AstroAid

AstroAid is an app for amateur astronomers that functions as an aid to visualizing what you will see through your telescope/camera lens when you use a particular eyepiece and, optionally, an optical aid (such as a Barlow lens). You can also pair a camera/imager with a telescope and determine what your camera/imager will see in its frame. This will be a big help for astro-imagers.
The app computes a number of parameters for your telescope/eyepiece/imager combination, such as magnification, actual field of view, visual magnitude limit, etc. and displays these values in tabular form.
Several astronomical catalogues are built in to the app (including Messier, NGC, IC, and many other object catalogues), and will be updated on-line occasionally. Images for these objects can be downloaded. All catalogues can be searched.
The app contains extensive lists of known vendor-supplied telescopes, camera lenses, eyepieces, imagers, and optical aids. You can also create your own custom entries if your equipment isn't listed (for example, if you made your own telescope). These custom entries are shared between your devices via iCloud (if available).