Although I have a USB microscope, I wanted something for my phone that I could use in the field. I bought the Lighthouse Phonescope (see Amazon link here). This is a lens attached to a very strong clip that should fit almost any phone. Here it is attached to my iPhone with an Otter case.
The clip spring is quite strong. I found it somewhat difficult myself; someone with weaker hands (like my wife) might not be able to do it at all.
I did find it slightly easier if I put it on from the side:
The actual lens can easily come out of the clip when not attached to a phone. It's not so loose that it is likely to fall out, but you could knock it out accidentally.
But in order to get that relatively flat, you'll need something at the other end of your phone. I used my wife's pill box, which was close enough.
So now the question is, how well does it work?
You need LOTS of light. That translucent pedestal will only let in so much. I was just using overhead lighting in my kitchen; that was insufficient, so I added a flashlight. I used the iPhone zoom magnification in addition to the Phonescope lens.
But remember that this is a fixed focal length. Is the ideal distance with the coin covered as it is for the Lincoln cent above, or should it be on the coin itself as it has to be with a silver dollar and can easily be with a half dollar?
What about a coin in a slab? The coin surface will be a little farther away. The iPhone camera will compensate for that somewhat, but the results were a little fuzzier:
I was unable to zoom at all when looking at a slab; the iPhone could not get focus when zoomed.
So, all things considered: this is a decent tool for raw coins, but not ideal for slabs.
Note: All my coins are in a safe deposit box. I keep nothing in my home.
Contests and giveaways: http://coins.aplawrence.com/2014/05/contests-and-giveaways.html