The smallest adapter is 49mm.
With another adapter E49 to E39 to add to your Summicron, you may be use Xume system.
Or adapter E52 (... another diameter) to E39 and use your currently available E52 (or what you have most).
You're right - 49mm is the smallest size. So I could use a step-up ring, but then my built-in hood is out of commission. I used these on my DSLR. They are very handy, but you just have to make sure it doesn't cause vignetting.