To test out my new lens, I took a few shots of plants around the house.
The first image was taken with a reference lens, the 80 mm f/2.8. Everything looks just fine here. You may notice the pentagonal bokeh in the background. That is due to the fact that the iris itself has five straight blades. The out of focus highlights in the background have the same shape as the lens aperture. Modern lenses tend to have more aperture blades and they also may be curved a bit to mitigate this effect which many might find distracting. Me, I'm fine with it most of the time.
Then, I mounted the newly purchased 120 mm and after developing the negatives, I was blown away by what I saw, but not in a good way... The bokeh had what I would describe as a 'dirty' look to it. The texture is very unpleasant and not something I would want in every image taken with this lens. Extremely upsetting. So, I took a closer look at the glass, and sure enough, it looked as though the lens had spent some time under water. Damn, a flood lens! That was not apparent from the pictures on the auction site. Hmm. I could not clean the funk off the front element of the lens, and since even the internal lens elements were messed up, I decided to try for a refund. Naturally, I was not able to get a response out of the seller, and ended up trading the lens in for parts at my local camera shop.
No one likes getting screwed like that, but I did learn something about how the quality of the bokeh can be used as a lens diagnostic. It was an interesting, if somewhat expensive experience. Fortunately, I was able to find a clean copy of the 120 mm f/5.6 later, so all's well that ends well.
