It is much more difficult to buy Binoculars than buying other items like the rifle scope, rangefinder or spotting scope. The considerations to be taken into account are multifarious in case of binoculars. It is not such in case of the smaller items. The consideration is in most cases confined to adjusting your budget to buy the required item. Of course there are a few very simple considerations to take care of while buying these articles.
Buying spotting scopes for exclusive use in photography requires that you go for the catdioptric scopes that make much better telephoto lenses than most other accessories used. You also have to take care of the necessary prismatic modifications required to adjust your spotting scopes for the purpose. Similarly, if you are concerned about low lights in the environment, you may look for the highest twilight factors in your spotting scopes. Weight will be a consideration if you wish to travel with the equipment frequently and for use in rough weather, a rubber armored equipment or having waterproof spotting scopes would be the ideal solution.
Most of the times however your major concern will be getting the best and sharpest image of the object you are viewing. Since spotting scope is used for viewing tiny or moving objects, single power eyepieces shall be much more useful than the zoom. Like the rifle scopes you can also use the ED glass lens or fluorite lens for use in the spotting scope so that the images are of real high quality.