I recently purchased a Diana lens with a Nikon adapter to fit on my 3100. The Diana camera is a plastic camera similar to the Holga, but introduced ten years prior. It is known for it's "dreamy" soft focus images.
To use the lens with the dSLR, you have to use completely manual settings. When I first got it, I tried it a bit inside, but didn't really get any kind of good pictures. This is a lens that likes a lot of light.
Morton Arboretum. It was a gorgeous morning, but unfortunately, it hadn't been spring quite long enough, and we were lucky to find what I think was the only green on the entire grounds with this patch of daffodils.
The Diana lens took some great images. While it is obviously not a lens for every day use, it is a lot of fun when looking to get a different effect than normal and having some fun. It takes a bit of futzing with settings to get the right balance of light and the focus correct, but as I take more pictures, I'm getting a better idea of how things work.