The Problem: The collapsible rubber lens hood that comes with the 40mm Summicron eventually weakens and rips free from the aluminum ring that screws it into the lens AND acts as a retainer for the series 5.5 filters that the Summicron uses. For me, the rubber came off the lens hood about the same time as my original Leitz UV series 5.5 filter wore out and needed replacing. So, two problems actually - inneffective hood shading and hard to find 5.5 filters. My Solution: Because a regular 39mm filter has a slightly different thread pitch than the 39mm hood's thread, you can screw in a 39mm filter thread about one full turn until it snugs up tightly but without damage to any threads. Then the rubberless hood screws into the 39mm filter, again finger tight. This forms a long hood ahead of the lens, but introduces vignetting in the corners. Filing out the corners of the hood ring to match the 3:2 rectangle, you can get rid of the vignetting and then have a hood with a nice tight light-shielding capability. I just blacken the filed/sandpapered aluminum with a few coats of a permanent marker. Another nice benefit is that the original snap-on lens cap, which is one of the great cap designs of all time, still fits snugly and pops off as easily as before.