If you search for "Stanhope cross" on eBay, you will see maybe 10 crosses that look just like this design, some wood, some bone, some other materials (maybe plastic for more recent ones).

So my conclusion is that this was an item made by the thousands, and maybe for decades in the late 1800s and early 1900s. The main company making Stanhope viewers was based in France, and a number of the eBay items have religious images, some obviously from France. There is more info on various web sites - one is the attached link. The French company making the viewers was in operation from 1859 - 1972!

Russians certainly could have made crosses and incorporated the viewers, but most of the eBay crosses indicated the images were from non-Russian sites or saints. The image in the viewer of any particular cross would be a clue of course to the origin. If you have a chance to see one again, see if you can make out the image. Some of the microphotographs have deteriorated, and whatever you do, DON'T try to clean the viewer with anything other than a very soft cloth or brush. Any kind of cleaner or solvent may completely ruin the image, which could be 150 years old.

A little more web searching will get you a lot more info, I'm sure!